UltarSound Machine Dr Fadhl Alakwaa
description
Transcript of UltarSound Machine Dr Fadhl Alakwaa
UltarSound MachineDr Fadhl Alakwaa
fadlworkgmailcom
What are the first things to account when purchasing new US equipment
bull Clinical applicationbull Operation Modesbull Transducersbull OTHERS
ndash DISOM amp STORAGE ndash PRINTERndash NETWORKING
EXCELLENT RESOURCES
bull Ultrasound Machine Comparison An Evaluation of Ergonomic Design Data Management Ease of Use and Image Quality
bull httpwwwcompareultrasoundcombull Objective measurements of image qualitybull Ultrasound Equipment Evaluation Project
CLINICAL APPLICATIONS
bull Breast Imaging of female (usually) breastsbull Cardiac Imaging of the heartbull Gynecologic Imaging of the female reproductive organsbull Radiology Imaging of the internal organs of the abdomenbull Obstetrics (sometimes combined with Gynecologic as in
OBGYN) Imaging of fetuses in vivobull Pediatrics Imaging of childrenbull Vascular Imaging of the (usually peripheral as in peripheral
vascular) arteries and veins of the vascular system (called lsquolsquocardiovascularrsquorsquo when combined with heart imaging)
bull (Note that lsquolsquointrarsquorsquo (from Latin) means into or inside lsquolsquotransrsquorsquo means through or across and lsquolsquoendorsquorsquo means within)
bull Endovaginal Imaging the female pelvis using the vagina as an acoustic window
bull Intracardiac Imaging from within the heartbull Intraoperative Imaging during a surgical procedurebull Intravascular Imaging of the interior of arteries
and veins from transducers inserted in thembull Laproscopic Imaging carried out to guide and
evaluate laparoscopic surgery made through small incisions
bull Musculoskeletal Imaging of muscles tendons and ligaments
bull Small parts High-resolution imaging applied to superficial tissues musculature and vessels near the skin surface
bull Transcranial Imaging through the skull (usually through windows such as the temple or eye) of the brain and its associated vasculature
bull Transesophageal Imaging of internal organs (especially the heart) from specially designed probes made to go inside the esophagus
bull Transorbital Imaging of the eye or through the eye as an acoustic window
bull Transrectal Imaging of the pelvis using the rectum as an acoustic window
bull Transthoracic External imaging from the surface of the chest
What do you need to know to be professional in US
bull Advantage of US OVER other modalitiesbull US developmentbull US physicsbull Ultrasound Terminology bull US clinical applicationsbull US componentsbull US Transducer typesbull US modesbull US specifications
Advantage of US OVER other modalities
US development
What is Ultrasound machine
bullUltrasound or ultrasonography is a medical imaging technique that uses high frequency
sound waves and their echoes bullBut what is the ultrasound waves
Krautkramer NDT Ultrasonic Systems
Spectrum of sound
Frequency range Hz Description Example
0 - 20 Infrasound Earth quake
20 - 20000 Audible sound Speech music
gt20000 Ultrasound Bat Quartz crystal
Medical ultrasound frequency is 1Mhz-10Mhzوعرضية طولية نوعيين صوتية الفوق الموجات
Krautkramer NDT Ultrasonic Systems
Direction of oscillation
Direction of propagationLongitudinal wave
Sound propagation
Krautkramer NDT Ultrasonic Systems
Direction of propagationTransverse waveDirection of oscillation
Sound propagation
Krautkramer NDT Ultrasonic Systems
Wave propagation
AirWater
Steel longSteel trans
330 ms
1480 ms
3250 ms
5920 ms
Longitudinal waves propagate in all kind of materialsTransverse waves only propagate in solid bodies Due to the different type of oscillation transverse wavestravel at lower speedsSound velocity mainly depends on the density and E-modulus of the material
Difference between EM and soundbull Material through which wave movesbull Medium not required for all wave types
ndash no medium required for electromagnetic wavesbull radiobull x-raysbull infraredbull ultraviolet
ndash medium is required for soundbull sound does not travel through vacuum
Talk louder I canrsquot hear
you
How to produce sound wave
bull By applying voltage on some material face likendash Quartzndash PZT
Krautkramer NDT Ultrasonic Systems
Piezoelectric Effect
Piezoelectrical Crystal (Quartz)
Battery
+
Krautkramer NDT Ultrasonic Systems
+
The crystal gets thicker due to a distortion of the crystal lattice
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
+
The effect inverses with polarity change
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
An alternating voltage generates crystal oscillations at the frequency f
U(f)
Sound wave with
frequency f
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
A short voltage pulse generates an oscillation at the crystallsquos resonantfrequency f0 OPERATING FREQUNCY
Short pulse lt ( 1 micros)
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
How to receive sound waves
A sound wave hitting a piezoelectric crystal induces crystal vibration which then causes electrical voltages at the crystal surfaces
Electrical energy
Piezoelectrical crystal Ultrasonic wave
Krautkramer NDT Ultrasonic Systems
N
Near field Far field
Focus Angle of divergenceCrystalAccoustical axis
D0
6
Sound field
Transducer array
bull Transducer = ARRAY OF PIEZOELECTRICAL ELEMENTS Typically 128 to 512
bull SPECFICATIONndash Materialndash ARRAY LENGHTndash Frequency rang
bull resolutionndash Depth CMndash Type
bull LINEAR ARRAYbull PHASED ARRAY
Ultrasound Display
bull One sound pulse producesndash one image scan line
bull one series of gray shade dots in a line
bull Multiple pulsesndash two dimensional image
obtained by moving direction in which sound transmitted
Real-time Scanning
Each pulse generates one lineExcept for multiple focal zones
one frame consists of many individual scan lines
lines framesPRF (Hz) = ------------ X--------------
frame sec
One pulse = one line
Linear Curved linear array Phased arraysectorEndocavitary Intraoperative
Transducer ArraysbullVirtually all commercial transducers are
arraysndashMultiple small elements in single housing
bullAllows sound beam to be electronicallyndashFocusedndashSteeredndashShaped
Electronic Scanning
bullTransducer ArraysndashMultiple small transducersndashActivated in groups
Electrical ScanningPerformed with transducer arrays
multiple elements inside transducer assembly arranged in either
a line (linear array)
concentric circles (annular array)
Curvilinear Array Linear Array
Linear Array ScanningTwo techniques for activating groups of linear
transducersSwitched Arrays
activate all elements in group at same timePhased Arrays
Activate group elements at slightly different timesimpose timing delays between activations of elements in group
Linear Switched ArraysbullElements energized as groups
ndashgroup acts like one large transducer
bullGroups moved up amp down through elements
ndashsame effect as manually translating
ndashvery fast scanning possible (several times per second)
bullresults in real time image
Linear Switched Arrays
Linear Phased ArraybullGroups of elements energizedndashsame as with switched arraysbullvoltage pulse applied to all
elements of a groupBUT
bullelements not all pulsed at same time
1
2
Linear Phased Arraybulltiming variations allow beam to
be ndashshapedndashsteeredndashfocused
Above arrows indicate timing variations
By activating bottom element first amp top last beam directed upward
Beam steered upward
Linear Phased Array
Above arrows indicate timing variationsBy activating top
element first amp bottom last beam directed
downward
Beam steered downward
By changing timing variations between pulses beam can be scanned from top to bottom
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
What are the first things to account when purchasing new US equipment
bull Clinical applicationbull Operation Modesbull Transducersbull OTHERS
ndash DISOM amp STORAGE ndash PRINTERndash NETWORKING
EXCELLENT RESOURCES
bull Ultrasound Machine Comparison An Evaluation of Ergonomic Design Data Management Ease of Use and Image Quality
bull httpwwwcompareultrasoundcombull Objective measurements of image qualitybull Ultrasound Equipment Evaluation Project
CLINICAL APPLICATIONS
bull Breast Imaging of female (usually) breastsbull Cardiac Imaging of the heartbull Gynecologic Imaging of the female reproductive organsbull Radiology Imaging of the internal organs of the abdomenbull Obstetrics (sometimes combined with Gynecologic as in
OBGYN) Imaging of fetuses in vivobull Pediatrics Imaging of childrenbull Vascular Imaging of the (usually peripheral as in peripheral
vascular) arteries and veins of the vascular system (called lsquolsquocardiovascularrsquorsquo when combined with heart imaging)
bull (Note that lsquolsquointrarsquorsquo (from Latin) means into or inside lsquolsquotransrsquorsquo means through or across and lsquolsquoendorsquorsquo means within)
bull Endovaginal Imaging the female pelvis using the vagina as an acoustic window
bull Intracardiac Imaging from within the heartbull Intraoperative Imaging during a surgical procedurebull Intravascular Imaging of the interior of arteries
and veins from transducers inserted in thembull Laproscopic Imaging carried out to guide and
evaluate laparoscopic surgery made through small incisions
bull Musculoskeletal Imaging of muscles tendons and ligaments
bull Small parts High-resolution imaging applied to superficial tissues musculature and vessels near the skin surface
bull Transcranial Imaging through the skull (usually through windows such as the temple or eye) of the brain and its associated vasculature
bull Transesophageal Imaging of internal organs (especially the heart) from specially designed probes made to go inside the esophagus
bull Transorbital Imaging of the eye or through the eye as an acoustic window
bull Transrectal Imaging of the pelvis using the rectum as an acoustic window
bull Transthoracic External imaging from the surface of the chest
What do you need to know to be professional in US
bull Advantage of US OVER other modalitiesbull US developmentbull US physicsbull Ultrasound Terminology bull US clinical applicationsbull US componentsbull US Transducer typesbull US modesbull US specifications
Advantage of US OVER other modalities
US development
What is Ultrasound machine
bullUltrasound or ultrasonography is a medical imaging technique that uses high frequency
sound waves and their echoes bullBut what is the ultrasound waves
Krautkramer NDT Ultrasonic Systems
Spectrum of sound
Frequency range Hz Description Example
0 - 20 Infrasound Earth quake
20 - 20000 Audible sound Speech music
gt20000 Ultrasound Bat Quartz crystal
Medical ultrasound frequency is 1Mhz-10Mhzوعرضية طولية نوعيين صوتية الفوق الموجات
Krautkramer NDT Ultrasonic Systems
Direction of oscillation
Direction of propagationLongitudinal wave
Sound propagation
Krautkramer NDT Ultrasonic Systems
Direction of propagationTransverse waveDirection of oscillation
Sound propagation
Krautkramer NDT Ultrasonic Systems
Wave propagation
AirWater
Steel longSteel trans
330 ms
1480 ms
3250 ms
5920 ms
Longitudinal waves propagate in all kind of materialsTransverse waves only propagate in solid bodies Due to the different type of oscillation transverse wavestravel at lower speedsSound velocity mainly depends on the density and E-modulus of the material
Difference between EM and soundbull Material through which wave movesbull Medium not required for all wave types
ndash no medium required for electromagnetic wavesbull radiobull x-raysbull infraredbull ultraviolet
ndash medium is required for soundbull sound does not travel through vacuum
Talk louder I canrsquot hear
you
How to produce sound wave
bull By applying voltage on some material face likendash Quartzndash PZT
Krautkramer NDT Ultrasonic Systems
Piezoelectric Effect
Piezoelectrical Crystal (Quartz)
Battery
+
Krautkramer NDT Ultrasonic Systems
+
The crystal gets thicker due to a distortion of the crystal lattice
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
+
The effect inverses with polarity change
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
An alternating voltage generates crystal oscillations at the frequency f
U(f)
Sound wave with
frequency f
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
A short voltage pulse generates an oscillation at the crystallsquos resonantfrequency f0 OPERATING FREQUNCY
Short pulse lt ( 1 micros)
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
How to receive sound waves
A sound wave hitting a piezoelectric crystal induces crystal vibration which then causes electrical voltages at the crystal surfaces
Electrical energy
Piezoelectrical crystal Ultrasonic wave
Krautkramer NDT Ultrasonic Systems
N
Near field Far field
Focus Angle of divergenceCrystalAccoustical axis
D0
6
Sound field
Transducer array
bull Transducer = ARRAY OF PIEZOELECTRICAL ELEMENTS Typically 128 to 512
bull SPECFICATIONndash Materialndash ARRAY LENGHTndash Frequency rang
bull resolutionndash Depth CMndash Type
bull LINEAR ARRAYbull PHASED ARRAY
Ultrasound Display
bull One sound pulse producesndash one image scan line
bull one series of gray shade dots in a line
bull Multiple pulsesndash two dimensional image
obtained by moving direction in which sound transmitted
Real-time Scanning
Each pulse generates one lineExcept for multiple focal zones
one frame consists of many individual scan lines
lines framesPRF (Hz) = ------------ X--------------
frame sec
One pulse = one line
Linear Curved linear array Phased arraysectorEndocavitary Intraoperative
Transducer ArraysbullVirtually all commercial transducers are
arraysndashMultiple small elements in single housing
bullAllows sound beam to be electronicallyndashFocusedndashSteeredndashShaped
Electronic Scanning
bullTransducer ArraysndashMultiple small transducersndashActivated in groups
Electrical ScanningPerformed with transducer arrays
multiple elements inside transducer assembly arranged in either
a line (linear array)
concentric circles (annular array)
Curvilinear Array Linear Array
Linear Array ScanningTwo techniques for activating groups of linear
transducersSwitched Arrays
activate all elements in group at same timePhased Arrays
Activate group elements at slightly different timesimpose timing delays between activations of elements in group
Linear Switched ArraysbullElements energized as groups
ndashgroup acts like one large transducer
bullGroups moved up amp down through elements
ndashsame effect as manually translating
ndashvery fast scanning possible (several times per second)
bullresults in real time image
Linear Switched Arrays
Linear Phased ArraybullGroups of elements energizedndashsame as with switched arraysbullvoltage pulse applied to all
elements of a groupBUT
bullelements not all pulsed at same time
1
2
Linear Phased Arraybulltiming variations allow beam to
be ndashshapedndashsteeredndashfocused
Above arrows indicate timing variations
By activating bottom element first amp top last beam directed upward
Beam steered upward
Linear Phased Array
Above arrows indicate timing variationsBy activating top
element first amp bottom last beam directed
downward
Beam steered downward
By changing timing variations between pulses beam can be scanned from top to bottom
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
EXCELLENT RESOURCES
bull Ultrasound Machine Comparison An Evaluation of Ergonomic Design Data Management Ease of Use and Image Quality
bull httpwwwcompareultrasoundcombull Objective measurements of image qualitybull Ultrasound Equipment Evaluation Project
CLINICAL APPLICATIONS
bull Breast Imaging of female (usually) breastsbull Cardiac Imaging of the heartbull Gynecologic Imaging of the female reproductive organsbull Radiology Imaging of the internal organs of the abdomenbull Obstetrics (sometimes combined with Gynecologic as in
OBGYN) Imaging of fetuses in vivobull Pediatrics Imaging of childrenbull Vascular Imaging of the (usually peripheral as in peripheral
vascular) arteries and veins of the vascular system (called lsquolsquocardiovascularrsquorsquo when combined with heart imaging)
bull (Note that lsquolsquointrarsquorsquo (from Latin) means into or inside lsquolsquotransrsquorsquo means through or across and lsquolsquoendorsquorsquo means within)
bull Endovaginal Imaging the female pelvis using the vagina as an acoustic window
bull Intracardiac Imaging from within the heartbull Intraoperative Imaging during a surgical procedurebull Intravascular Imaging of the interior of arteries
and veins from transducers inserted in thembull Laproscopic Imaging carried out to guide and
evaluate laparoscopic surgery made through small incisions
bull Musculoskeletal Imaging of muscles tendons and ligaments
bull Small parts High-resolution imaging applied to superficial tissues musculature and vessels near the skin surface
bull Transcranial Imaging through the skull (usually through windows such as the temple or eye) of the brain and its associated vasculature
bull Transesophageal Imaging of internal organs (especially the heart) from specially designed probes made to go inside the esophagus
bull Transorbital Imaging of the eye or through the eye as an acoustic window
bull Transrectal Imaging of the pelvis using the rectum as an acoustic window
bull Transthoracic External imaging from the surface of the chest
What do you need to know to be professional in US
bull Advantage of US OVER other modalitiesbull US developmentbull US physicsbull Ultrasound Terminology bull US clinical applicationsbull US componentsbull US Transducer typesbull US modesbull US specifications
Advantage of US OVER other modalities
US development
What is Ultrasound machine
bullUltrasound or ultrasonography is a medical imaging technique that uses high frequency
sound waves and their echoes bullBut what is the ultrasound waves
Krautkramer NDT Ultrasonic Systems
Spectrum of sound
Frequency range Hz Description Example
0 - 20 Infrasound Earth quake
20 - 20000 Audible sound Speech music
gt20000 Ultrasound Bat Quartz crystal
Medical ultrasound frequency is 1Mhz-10Mhzوعرضية طولية نوعيين صوتية الفوق الموجات
Krautkramer NDT Ultrasonic Systems
Direction of oscillation
Direction of propagationLongitudinal wave
Sound propagation
Krautkramer NDT Ultrasonic Systems
Direction of propagationTransverse waveDirection of oscillation
Sound propagation
Krautkramer NDT Ultrasonic Systems
Wave propagation
AirWater
Steel longSteel trans
330 ms
1480 ms
3250 ms
5920 ms
Longitudinal waves propagate in all kind of materialsTransverse waves only propagate in solid bodies Due to the different type of oscillation transverse wavestravel at lower speedsSound velocity mainly depends on the density and E-modulus of the material
Difference between EM and soundbull Material through which wave movesbull Medium not required for all wave types
ndash no medium required for electromagnetic wavesbull radiobull x-raysbull infraredbull ultraviolet
ndash medium is required for soundbull sound does not travel through vacuum
Talk louder I canrsquot hear
you
How to produce sound wave
bull By applying voltage on some material face likendash Quartzndash PZT
Krautkramer NDT Ultrasonic Systems
Piezoelectric Effect
Piezoelectrical Crystal (Quartz)
Battery
+
Krautkramer NDT Ultrasonic Systems
+
The crystal gets thicker due to a distortion of the crystal lattice
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
+
The effect inverses with polarity change
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
An alternating voltage generates crystal oscillations at the frequency f
U(f)
Sound wave with
frequency f
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
A short voltage pulse generates an oscillation at the crystallsquos resonantfrequency f0 OPERATING FREQUNCY
Short pulse lt ( 1 micros)
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
How to receive sound waves
A sound wave hitting a piezoelectric crystal induces crystal vibration which then causes electrical voltages at the crystal surfaces
Electrical energy
Piezoelectrical crystal Ultrasonic wave
Krautkramer NDT Ultrasonic Systems
N
Near field Far field
Focus Angle of divergenceCrystalAccoustical axis
D0
6
Sound field
Transducer array
bull Transducer = ARRAY OF PIEZOELECTRICAL ELEMENTS Typically 128 to 512
bull SPECFICATIONndash Materialndash ARRAY LENGHTndash Frequency rang
bull resolutionndash Depth CMndash Type
bull LINEAR ARRAYbull PHASED ARRAY
Ultrasound Display
bull One sound pulse producesndash one image scan line
bull one series of gray shade dots in a line
bull Multiple pulsesndash two dimensional image
obtained by moving direction in which sound transmitted
Real-time Scanning
Each pulse generates one lineExcept for multiple focal zones
one frame consists of many individual scan lines
lines framesPRF (Hz) = ------------ X--------------
frame sec
One pulse = one line
Linear Curved linear array Phased arraysectorEndocavitary Intraoperative
Transducer ArraysbullVirtually all commercial transducers are
arraysndashMultiple small elements in single housing
bullAllows sound beam to be electronicallyndashFocusedndashSteeredndashShaped
Electronic Scanning
bullTransducer ArraysndashMultiple small transducersndashActivated in groups
Electrical ScanningPerformed with transducer arrays
multiple elements inside transducer assembly arranged in either
a line (linear array)
concentric circles (annular array)
Curvilinear Array Linear Array
Linear Array ScanningTwo techniques for activating groups of linear
transducersSwitched Arrays
activate all elements in group at same timePhased Arrays
Activate group elements at slightly different timesimpose timing delays between activations of elements in group
Linear Switched ArraysbullElements energized as groups
ndashgroup acts like one large transducer
bullGroups moved up amp down through elements
ndashsame effect as manually translating
ndashvery fast scanning possible (several times per second)
bullresults in real time image
Linear Switched Arrays
Linear Phased ArraybullGroups of elements energizedndashsame as with switched arraysbullvoltage pulse applied to all
elements of a groupBUT
bullelements not all pulsed at same time
1
2
Linear Phased Arraybulltiming variations allow beam to
be ndashshapedndashsteeredndashfocused
Above arrows indicate timing variations
By activating bottom element first amp top last beam directed upward
Beam steered upward
Linear Phased Array
Above arrows indicate timing variationsBy activating top
element first amp bottom last beam directed
downward
Beam steered downward
By changing timing variations between pulses beam can be scanned from top to bottom
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
CLINICAL APPLICATIONS
bull Breast Imaging of female (usually) breastsbull Cardiac Imaging of the heartbull Gynecologic Imaging of the female reproductive organsbull Radiology Imaging of the internal organs of the abdomenbull Obstetrics (sometimes combined with Gynecologic as in
OBGYN) Imaging of fetuses in vivobull Pediatrics Imaging of childrenbull Vascular Imaging of the (usually peripheral as in peripheral
vascular) arteries and veins of the vascular system (called lsquolsquocardiovascularrsquorsquo when combined with heart imaging)
bull (Note that lsquolsquointrarsquorsquo (from Latin) means into or inside lsquolsquotransrsquorsquo means through or across and lsquolsquoendorsquorsquo means within)
bull Endovaginal Imaging the female pelvis using the vagina as an acoustic window
bull Intracardiac Imaging from within the heartbull Intraoperative Imaging during a surgical procedurebull Intravascular Imaging of the interior of arteries
and veins from transducers inserted in thembull Laproscopic Imaging carried out to guide and
evaluate laparoscopic surgery made through small incisions
bull Musculoskeletal Imaging of muscles tendons and ligaments
bull Small parts High-resolution imaging applied to superficial tissues musculature and vessels near the skin surface
bull Transcranial Imaging through the skull (usually through windows such as the temple or eye) of the brain and its associated vasculature
bull Transesophageal Imaging of internal organs (especially the heart) from specially designed probes made to go inside the esophagus
bull Transorbital Imaging of the eye or through the eye as an acoustic window
bull Transrectal Imaging of the pelvis using the rectum as an acoustic window
bull Transthoracic External imaging from the surface of the chest
What do you need to know to be professional in US
bull Advantage of US OVER other modalitiesbull US developmentbull US physicsbull Ultrasound Terminology bull US clinical applicationsbull US componentsbull US Transducer typesbull US modesbull US specifications
Advantage of US OVER other modalities
US development
What is Ultrasound machine
bullUltrasound or ultrasonography is a medical imaging technique that uses high frequency
sound waves and their echoes bullBut what is the ultrasound waves
Krautkramer NDT Ultrasonic Systems
Spectrum of sound
Frequency range Hz Description Example
0 - 20 Infrasound Earth quake
20 - 20000 Audible sound Speech music
gt20000 Ultrasound Bat Quartz crystal
Medical ultrasound frequency is 1Mhz-10Mhzوعرضية طولية نوعيين صوتية الفوق الموجات
Krautkramer NDT Ultrasonic Systems
Direction of oscillation
Direction of propagationLongitudinal wave
Sound propagation
Krautkramer NDT Ultrasonic Systems
Direction of propagationTransverse waveDirection of oscillation
Sound propagation
Krautkramer NDT Ultrasonic Systems
Wave propagation
AirWater
Steel longSteel trans
330 ms
1480 ms
3250 ms
5920 ms
Longitudinal waves propagate in all kind of materialsTransverse waves only propagate in solid bodies Due to the different type of oscillation transverse wavestravel at lower speedsSound velocity mainly depends on the density and E-modulus of the material
Difference between EM and soundbull Material through which wave movesbull Medium not required for all wave types
ndash no medium required for electromagnetic wavesbull radiobull x-raysbull infraredbull ultraviolet
ndash medium is required for soundbull sound does not travel through vacuum
Talk louder I canrsquot hear
you
How to produce sound wave
bull By applying voltage on some material face likendash Quartzndash PZT
Krautkramer NDT Ultrasonic Systems
Piezoelectric Effect
Piezoelectrical Crystal (Quartz)
Battery
+
Krautkramer NDT Ultrasonic Systems
+
The crystal gets thicker due to a distortion of the crystal lattice
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
+
The effect inverses with polarity change
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
An alternating voltage generates crystal oscillations at the frequency f
U(f)
Sound wave with
frequency f
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
A short voltage pulse generates an oscillation at the crystallsquos resonantfrequency f0 OPERATING FREQUNCY
Short pulse lt ( 1 micros)
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
How to receive sound waves
A sound wave hitting a piezoelectric crystal induces crystal vibration which then causes electrical voltages at the crystal surfaces
Electrical energy
Piezoelectrical crystal Ultrasonic wave
Krautkramer NDT Ultrasonic Systems
N
Near field Far field
Focus Angle of divergenceCrystalAccoustical axis
D0
6
Sound field
Transducer array
bull Transducer = ARRAY OF PIEZOELECTRICAL ELEMENTS Typically 128 to 512
bull SPECFICATIONndash Materialndash ARRAY LENGHTndash Frequency rang
bull resolutionndash Depth CMndash Type
bull LINEAR ARRAYbull PHASED ARRAY
Ultrasound Display
bull One sound pulse producesndash one image scan line
bull one series of gray shade dots in a line
bull Multiple pulsesndash two dimensional image
obtained by moving direction in which sound transmitted
Real-time Scanning
Each pulse generates one lineExcept for multiple focal zones
one frame consists of many individual scan lines
lines framesPRF (Hz) = ------------ X--------------
frame sec
One pulse = one line
Linear Curved linear array Phased arraysectorEndocavitary Intraoperative
Transducer ArraysbullVirtually all commercial transducers are
arraysndashMultiple small elements in single housing
bullAllows sound beam to be electronicallyndashFocusedndashSteeredndashShaped
Electronic Scanning
bullTransducer ArraysndashMultiple small transducersndashActivated in groups
Electrical ScanningPerformed with transducer arrays
multiple elements inside transducer assembly arranged in either
a line (linear array)
concentric circles (annular array)
Curvilinear Array Linear Array
Linear Array ScanningTwo techniques for activating groups of linear
transducersSwitched Arrays
activate all elements in group at same timePhased Arrays
Activate group elements at slightly different timesimpose timing delays between activations of elements in group
Linear Switched ArraysbullElements energized as groups
ndashgroup acts like one large transducer
bullGroups moved up amp down through elements
ndashsame effect as manually translating
ndashvery fast scanning possible (several times per second)
bullresults in real time image
Linear Switched Arrays
Linear Phased ArraybullGroups of elements energizedndashsame as with switched arraysbullvoltage pulse applied to all
elements of a groupBUT
bullelements not all pulsed at same time
1
2
Linear Phased Arraybulltiming variations allow beam to
be ndashshapedndashsteeredndashfocused
Above arrows indicate timing variations
By activating bottom element first amp top last beam directed upward
Beam steered upward
Linear Phased Array
Above arrows indicate timing variationsBy activating top
element first amp bottom last beam directed
downward
Beam steered downward
By changing timing variations between pulses beam can be scanned from top to bottom
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
bull (Note that lsquolsquointrarsquorsquo (from Latin) means into or inside lsquolsquotransrsquorsquo means through or across and lsquolsquoendorsquorsquo means within)
bull Endovaginal Imaging the female pelvis using the vagina as an acoustic window
bull Intracardiac Imaging from within the heartbull Intraoperative Imaging during a surgical procedurebull Intravascular Imaging of the interior of arteries
and veins from transducers inserted in thembull Laproscopic Imaging carried out to guide and
evaluate laparoscopic surgery made through small incisions
bull Musculoskeletal Imaging of muscles tendons and ligaments
bull Small parts High-resolution imaging applied to superficial tissues musculature and vessels near the skin surface
bull Transcranial Imaging through the skull (usually through windows such as the temple or eye) of the brain and its associated vasculature
bull Transesophageal Imaging of internal organs (especially the heart) from specially designed probes made to go inside the esophagus
bull Transorbital Imaging of the eye or through the eye as an acoustic window
bull Transrectal Imaging of the pelvis using the rectum as an acoustic window
bull Transthoracic External imaging from the surface of the chest
What do you need to know to be professional in US
bull Advantage of US OVER other modalitiesbull US developmentbull US physicsbull Ultrasound Terminology bull US clinical applicationsbull US componentsbull US Transducer typesbull US modesbull US specifications
Advantage of US OVER other modalities
US development
What is Ultrasound machine
bullUltrasound or ultrasonography is a medical imaging technique that uses high frequency
sound waves and their echoes bullBut what is the ultrasound waves
Krautkramer NDT Ultrasonic Systems
Spectrum of sound
Frequency range Hz Description Example
0 - 20 Infrasound Earth quake
20 - 20000 Audible sound Speech music
gt20000 Ultrasound Bat Quartz crystal
Medical ultrasound frequency is 1Mhz-10Mhzوعرضية طولية نوعيين صوتية الفوق الموجات
Krautkramer NDT Ultrasonic Systems
Direction of oscillation
Direction of propagationLongitudinal wave
Sound propagation
Krautkramer NDT Ultrasonic Systems
Direction of propagationTransverse waveDirection of oscillation
Sound propagation
Krautkramer NDT Ultrasonic Systems
Wave propagation
AirWater
Steel longSteel trans
330 ms
1480 ms
3250 ms
5920 ms
Longitudinal waves propagate in all kind of materialsTransverse waves only propagate in solid bodies Due to the different type of oscillation transverse wavestravel at lower speedsSound velocity mainly depends on the density and E-modulus of the material
Difference between EM and soundbull Material through which wave movesbull Medium not required for all wave types
ndash no medium required for electromagnetic wavesbull radiobull x-raysbull infraredbull ultraviolet
ndash medium is required for soundbull sound does not travel through vacuum
Talk louder I canrsquot hear
you
How to produce sound wave
bull By applying voltage on some material face likendash Quartzndash PZT
Krautkramer NDT Ultrasonic Systems
Piezoelectric Effect
Piezoelectrical Crystal (Quartz)
Battery
+
Krautkramer NDT Ultrasonic Systems
+
The crystal gets thicker due to a distortion of the crystal lattice
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
+
The effect inverses with polarity change
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
An alternating voltage generates crystal oscillations at the frequency f
U(f)
Sound wave with
frequency f
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
A short voltage pulse generates an oscillation at the crystallsquos resonantfrequency f0 OPERATING FREQUNCY
Short pulse lt ( 1 micros)
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
How to receive sound waves
A sound wave hitting a piezoelectric crystal induces crystal vibration which then causes electrical voltages at the crystal surfaces
Electrical energy
Piezoelectrical crystal Ultrasonic wave
Krautkramer NDT Ultrasonic Systems
N
Near field Far field
Focus Angle of divergenceCrystalAccoustical axis
D0
6
Sound field
Transducer array
bull Transducer = ARRAY OF PIEZOELECTRICAL ELEMENTS Typically 128 to 512
bull SPECFICATIONndash Materialndash ARRAY LENGHTndash Frequency rang
bull resolutionndash Depth CMndash Type
bull LINEAR ARRAYbull PHASED ARRAY
Ultrasound Display
bull One sound pulse producesndash one image scan line
bull one series of gray shade dots in a line
bull Multiple pulsesndash two dimensional image
obtained by moving direction in which sound transmitted
Real-time Scanning
Each pulse generates one lineExcept for multiple focal zones
one frame consists of many individual scan lines
lines framesPRF (Hz) = ------------ X--------------
frame sec
One pulse = one line
Linear Curved linear array Phased arraysectorEndocavitary Intraoperative
Transducer ArraysbullVirtually all commercial transducers are
arraysndashMultiple small elements in single housing
bullAllows sound beam to be electronicallyndashFocusedndashSteeredndashShaped
Electronic Scanning
bullTransducer ArraysndashMultiple small transducersndashActivated in groups
Electrical ScanningPerformed with transducer arrays
multiple elements inside transducer assembly arranged in either
a line (linear array)
concentric circles (annular array)
Curvilinear Array Linear Array
Linear Array ScanningTwo techniques for activating groups of linear
transducersSwitched Arrays
activate all elements in group at same timePhased Arrays
Activate group elements at slightly different timesimpose timing delays between activations of elements in group
Linear Switched ArraysbullElements energized as groups
ndashgroup acts like one large transducer
bullGroups moved up amp down through elements
ndashsame effect as manually translating
ndashvery fast scanning possible (several times per second)
bullresults in real time image
Linear Switched Arrays
Linear Phased ArraybullGroups of elements energizedndashsame as with switched arraysbullvoltage pulse applied to all
elements of a groupBUT
bullelements not all pulsed at same time
1
2
Linear Phased Arraybulltiming variations allow beam to
be ndashshapedndashsteeredndashfocused
Above arrows indicate timing variations
By activating bottom element first amp top last beam directed upward
Beam steered upward
Linear Phased Array
Above arrows indicate timing variationsBy activating top
element first amp bottom last beam directed
downward
Beam steered downward
By changing timing variations between pulses beam can be scanned from top to bottom
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
bull Intracardiac Imaging from within the heartbull Intraoperative Imaging during a surgical procedurebull Intravascular Imaging of the interior of arteries
and veins from transducers inserted in thembull Laproscopic Imaging carried out to guide and
evaluate laparoscopic surgery made through small incisions
bull Musculoskeletal Imaging of muscles tendons and ligaments
bull Small parts High-resolution imaging applied to superficial tissues musculature and vessels near the skin surface
bull Transcranial Imaging through the skull (usually through windows such as the temple or eye) of the brain and its associated vasculature
bull Transesophageal Imaging of internal organs (especially the heart) from specially designed probes made to go inside the esophagus
bull Transorbital Imaging of the eye or through the eye as an acoustic window
bull Transrectal Imaging of the pelvis using the rectum as an acoustic window
bull Transthoracic External imaging from the surface of the chest
What do you need to know to be professional in US
bull Advantage of US OVER other modalitiesbull US developmentbull US physicsbull Ultrasound Terminology bull US clinical applicationsbull US componentsbull US Transducer typesbull US modesbull US specifications
Advantage of US OVER other modalities
US development
What is Ultrasound machine
bullUltrasound or ultrasonography is a medical imaging technique that uses high frequency
sound waves and their echoes bullBut what is the ultrasound waves
Krautkramer NDT Ultrasonic Systems
Spectrum of sound
Frequency range Hz Description Example
0 - 20 Infrasound Earth quake
20 - 20000 Audible sound Speech music
gt20000 Ultrasound Bat Quartz crystal
Medical ultrasound frequency is 1Mhz-10Mhzوعرضية طولية نوعيين صوتية الفوق الموجات
Krautkramer NDT Ultrasonic Systems
Direction of oscillation
Direction of propagationLongitudinal wave
Sound propagation
Krautkramer NDT Ultrasonic Systems
Direction of propagationTransverse waveDirection of oscillation
Sound propagation
Krautkramer NDT Ultrasonic Systems
Wave propagation
AirWater
Steel longSteel trans
330 ms
1480 ms
3250 ms
5920 ms
Longitudinal waves propagate in all kind of materialsTransverse waves only propagate in solid bodies Due to the different type of oscillation transverse wavestravel at lower speedsSound velocity mainly depends on the density and E-modulus of the material
Difference between EM and soundbull Material through which wave movesbull Medium not required for all wave types
ndash no medium required for electromagnetic wavesbull radiobull x-raysbull infraredbull ultraviolet
ndash medium is required for soundbull sound does not travel through vacuum
Talk louder I canrsquot hear
you
How to produce sound wave
bull By applying voltage on some material face likendash Quartzndash PZT
Krautkramer NDT Ultrasonic Systems
Piezoelectric Effect
Piezoelectrical Crystal (Quartz)
Battery
+
Krautkramer NDT Ultrasonic Systems
+
The crystal gets thicker due to a distortion of the crystal lattice
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
+
The effect inverses with polarity change
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
An alternating voltage generates crystal oscillations at the frequency f
U(f)
Sound wave with
frequency f
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
A short voltage pulse generates an oscillation at the crystallsquos resonantfrequency f0 OPERATING FREQUNCY
Short pulse lt ( 1 micros)
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
How to receive sound waves
A sound wave hitting a piezoelectric crystal induces crystal vibration which then causes electrical voltages at the crystal surfaces
Electrical energy
Piezoelectrical crystal Ultrasonic wave
Krautkramer NDT Ultrasonic Systems
N
Near field Far field
Focus Angle of divergenceCrystalAccoustical axis
D0
6
Sound field
Transducer array
bull Transducer = ARRAY OF PIEZOELECTRICAL ELEMENTS Typically 128 to 512
bull SPECFICATIONndash Materialndash ARRAY LENGHTndash Frequency rang
bull resolutionndash Depth CMndash Type
bull LINEAR ARRAYbull PHASED ARRAY
Ultrasound Display
bull One sound pulse producesndash one image scan line
bull one series of gray shade dots in a line
bull Multiple pulsesndash two dimensional image
obtained by moving direction in which sound transmitted
Real-time Scanning
Each pulse generates one lineExcept for multiple focal zones
one frame consists of many individual scan lines
lines framesPRF (Hz) = ------------ X--------------
frame sec
One pulse = one line
Linear Curved linear array Phased arraysectorEndocavitary Intraoperative
Transducer ArraysbullVirtually all commercial transducers are
arraysndashMultiple small elements in single housing
bullAllows sound beam to be electronicallyndashFocusedndashSteeredndashShaped
Electronic Scanning
bullTransducer ArraysndashMultiple small transducersndashActivated in groups
Electrical ScanningPerformed with transducer arrays
multiple elements inside transducer assembly arranged in either
a line (linear array)
concentric circles (annular array)
Curvilinear Array Linear Array
Linear Array ScanningTwo techniques for activating groups of linear
transducersSwitched Arrays
activate all elements in group at same timePhased Arrays
Activate group elements at slightly different timesimpose timing delays between activations of elements in group
Linear Switched ArraysbullElements energized as groups
ndashgroup acts like one large transducer
bullGroups moved up amp down through elements
ndashsame effect as manually translating
ndashvery fast scanning possible (several times per second)
bullresults in real time image
Linear Switched Arrays
Linear Phased ArraybullGroups of elements energizedndashsame as with switched arraysbullvoltage pulse applied to all
elements of a groupBUT
bullelements not all pulsed at same time
1
2
Linear Phased Arraybulltiming variations allow beam to
be ndashshapedndashsteeredndashfocused
Above arrows indicate timing variations
By activating bottom element first amp top last beam directed upward
Beam steered upward
Linear Phased Array
Above arrows indicate timing variationsBy activating top
element first amp bottom last beam directed
downward
Beam steered downward
By changing timing variations between pulses beam can be scanned from top to bottom
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
bull Small parts High-resolution imaging applied to superficial tissues musculature and vessels near the skin surface
bull Transcranial Imaging through the skull (usually through windows such as the temple or eye) of the brain and its associated vasculature
bull Transesophageal Imaging of internal organs (especially the heart) from specially designed probes made to go inside the esophagus
bull Transorbital Imaging of the eye or through the eye as an acoustic window
bull Transrectal Imaging of the pelvis using the rectum as an acoustic window
bull Transthoracic External imaging from the surface of the chest
What do you need to know to be professional in US
bull Advantage of US OVER other modalitiesbull US developmentbull US physicsbull Ultrasound Terminology bull US clinical applicationsbull US componentsbull US Transducer typesbull US modesbull US specifications
Advantage of US OVER other modalities
US development
What is Ultrasound machine
bullUltrasound or ultrasonography is a medical imaging technique that uses high frequency
sound waves and their echoes bullBut what is the ultrasound waves
Krautkramer NDT Ultrasonic Systems
Spectrum of sound
Frequency range Hz Description Example
0 - 20 Infrasound Earth quake
20 - 20000 Audible sound Speech music
gt20000 Ultrasound Bat Quartz crystal
Medical ultrasound frequency is 1Mhz-10Mhzوعرضية طولية نوعيين صوتية الفوق الموجات
Krautkramer NDT Ultrasonic Systems
Direction of oscillation
Direction of propagationLongitudinal wave
Sound propagation
Krautkramer NDT Ultrasonic Systems
Direction of propagationTransverse waveDirection of oscillation
Sound propagation
Krautkramer NDT Ultrasonic Systems
Wave propagation
AirWater
Steel longSteel trans
330 ms
1480 ms
3250 ms
5920 ms
Longitudinal waves propagate in all kind of materialsTransverse waves only propagate in solid bodies Due to the different type of oscillation transverse wavestravel at lower speedsSound velocity mainly depends on the density and E-modulus of the material
Difference between EM and soundbull Material through which wave movesbull Medium not required for all wave types
ndash no medium required for electromagnetic wavesbull radiobull x-raysbull infraredbull ultraviolet
ndash medium is required for soundbull sound does not travel through vacuum
Talk louder I canrsquot hear
you
How to produce sound wave
bull By applying voltage on some material face likendash Quartzndash PZT
Krautkramer NDT Ultrasonic Systems
Piezoelectric Effect
Piezoelectrical Crystal (Quartz)
Battery
+
Krautkramer NDT Ultrasonic Systems
+
The crystal gets thicker due to a distortion of the crystal lattice
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
+
The effect inverses with polarity change
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
An alternating voltage generates crystal oscillations at the frequency f
U(f)
Sound wave with
frequency f
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
A short voltage pulse generates an oscillation at the crystallsquos resonantfrequency f0 OPERATING FREQUNCY
Short pulse lt ( 1 micros)
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
How to receive sound waves
A sound wave hitting a piezoelectric crystal induces crystal vibration which then causes electrical voltages at the crystal surfaces
Electrical energy
Piezoelectrical crystal Ultrasonic wave
Krautkramer NDT Ultrasonic Systems
N
Near field Far field
Focus Angle of divergenceCrystalAccoustical axis
D0
6
Sound field
Transducer array
bull Transducer = ARRAY OF PIEZOELECTRICAL ELEMENTS Typically 128 to 512
bull SPECFICATIONndash Materialndash ARRAY LENGHTndash Frequency rang
bull resolutionndash Depth CMndash Type
bull LINEAR ARRAYbull PHASED ARRAY
Ultrasound Display
bull One sound pulse producesndash one image scan line
bull one series of gray shade dots in a line
bull Multiple pulsesndash two dimensional image
obtained by moving direction in which sound transmitted
Real-time Scanning
Each pulse generates one lineExcept for multiple focal zones
one frame consists of many individual scan lines
lines framesPRF (Hz) = ------------ X--------------
frame sec
One pulse = one line
Linear Curved linear array Phased arraysectorEndocavitary Intraoperative
Transducer ArraysbullVirtually all commercial transducers are
arraysndashMultiple small elements in single housing
bullAllows sound beam to be electronicallyndashFocusedndashSteeredndashShaped
Electronic Scanning
bullTransducer ArraysndashMultiple small transducersndashActivated in groups
Electrical ScanningPerformed with transducer arrays
multiple elements inside transducer assembly arranged in either
a line (linear array)
concentric circles (annular array)
Curvilinear Array Linear Array
Linear Array ScanningTwo techniques for activating groups of linear
transducersSwitched Arrays
activate all elements in group at same timePhased Arrays
Activate group elements at slightly different timesimpose timing delays between activations of elements in group
Linear Switched ArraysbullElements energized as groups
ndashgroup acts like one large transducer
bullGroups moved up amp down through elements
ndashsame effect as manually translating
ndashvery fast scanning possible (several times per second)
bullresults in real time image
Linear Switched Arrays
Linear Phased ArraybullGroups of elements energizedndashsame as with switched arraysbullvoltage pulse applied to all
elements of a groupBUT
bullelements not all pulsed at same time
1
2
Linear Phased Arraybulltiming variations allow beam to
be ndashshapedndashsteeredndashfocused
Above arrows indicate timing variations
By activating bottom element first amp top last beam directed upward
Beam steered upward
Linear Phased Array
Above arrows indicate timing variationsBy activating top
element first amp bottom last beam directed
downward
Beam steered downward
By changing timing variations between pulses beam can be scanned from top to bottom
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
What do you need to know to be professional in US
bull Advantage of US OVER other modalitiesbull US developmentbull US physicsbull Ultrasound Terminology bull US clinical applicationsbull US componentsbull US Transducer typesbull US modesbull US specifications
Advantage of US OVER other modalities
US development
What is Ultrasound machine
bullUltrasound or ultrasonography is a medical imaging technique that uses high frequency
sound waves and their echoes bullBut what is the ultrasound waves
Krautkramer NDT Ultrasonic Systems
Spectrum of sound
Frequency range Hz Description Example
0 - 20 Infrasound Earth quake
20 - 20000 Audible sound Speech music
gt20000 Ultrasound Bat Quartz crystal
Medical ultrasound frequency is 1Mhz-10Mhzوعرضية طولية نوعيين صوتية الفوق الموجات
Krautkramer NDT Ultrasonic Systems
Direction of oscillation
Direction of propagationLongitudinal wave
Sound propagation
Krautkramer NDT Ultrasonic Systems
Direction of propagationTransverse waveDirection of oscillation
Sound propagation
Krautkramer NDT Ultrasonic Systems
Wave propagation
AirWater
Steel longSteel trans
330 ms
1480 ms
3250 ms
5920 ms
Longitudinal waves propagate in all kind of materialsTransverse waves only propagate in solid bodies Due to the different type of oscillation transverse wavestravel at lower speedsSound velocity mainly depends on the density and E-modulus of the material
Difference between EM and soundbull Material through which wave movesbull Medium not required for all wave types
ndash no medium required for electromagnetic wavesbull radiobull x-raysbull infraredbull ultraviolet
ndash medium is required for soundbull sound does not travel through vacuum
Talk louder I canrsquot hear
you
How to produce sound wave
bull By applying voltage on some material face likendash Quartzndash PZT
Krautkramer NDT Ultrasonic Systems
Piezoelectric Effect
Piezoelectrical Crystal (Quartz)
Battery
+
Krautkramer NDT Ultrasonic Systems
+
The crystal gets thicker due to a distortion of the crystal lattice
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
+
The effect inverses with polarity change
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
An alternating voltage generates crystal oscillations at the frequency f
U(f)
Sound wave with
frequency f
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
A short voltage pulse generates an oscillation at the crystallsquos resonantfrequency f0 OPERATING FREQUNCY
Short pulse lt ( 1 micros)
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
How to receive sound waves
A sound wave hitting a piezoelectric crystal induces crystal vibration which then causes electrical voltages at the crystal surfaces
Electrical energy
Piezoelectrical crystal Ultrasonic wave
Krautkramer NDT Ultrasonic Systems
N
Near field Far field
Focus Angle of divergenceCrystalAccoustical axis
D0
6
Sound field
Transducer array
bull Transducer = ARRAY OF PIEZOELECTRICAL ELEMENTS Typically 128 to 512
bull SPECFICATIONndash Materialndash ARRAY LENGHTndash Frequency rang
bull resolutionndash Depth CMndash Type
bull LINEAR ARRAYbull PHASED ARRAY
Ultrasound Display
bull One sound pulse producesndash one image scan line
bull one series of gray shade dots in a line
bull Multiple pulsesndash two dimensional image
obtained by moving direction in which sound transmitted
Real-time Scanning
Each pulse generates one lineExcept for multiple focal zones
one frame consists of many individual scan lines
lines framesPRF (Hz) = ------------ X--------------
frame sec
One pulse = one line
Linear Curved linear array Phased arraysectorEndocavitary Intraoperative
Transducer ArraysbullVirtually all commercial transducers are
arraysndashMultiple small elements in single housing
bullAllows sound beam to be electronicallyndashFocusedndashSteeredndashShaped
Electronic Scanning
bullTransducer ArraysndashMultiple small transducersndashActivated in groups
Electrical ScanningPerformed with transducer arrays
multiple elements inside transducer assembly arranged in either
a line (linear array)
concentric circles (annular array)
Curvilinear Array Linear Array
Linear Array ScanningTwo techniques for activating groups of linear
transducersSwitched Arrays
activate all elements in group at same timePhased Arrays
Activate group elements at slightly different timesimpose timing delays between activations of elements in group
Linear Switched ArraysbullElements energized as groups
ndashgroup acts like one large transducer
bullGroups moved up amp down through elements
ndashsame effect as manually translating
ndashvery fast scanning possible (several times per second)
bullresults in real time image
Linear Switched Arrays
Linear Phased ArraybullGroups of elements energizedndashsame as with switched arraysbullvoltage pulse applied to all
elements of a groupBUT
bullelements not all pulsed at same time
1
2
Linear Phased Arraybulltiming variations allow beam to
be ndashshapedndashsteeredndashfocused
Above arrows indicate timing variations
By activating bottom element first amp top last beam directed upward
Beam steered upward
Linear Phased Array
Above arrows indicate timing variationsBy activating top
element first amp bottom last beam directed
downward
Beam steered downward
By changing timing variations between pulses beam can be scanned from top to bottom
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Advantage of US OVER other modalities
US development
What is Ultrasound machine
bullUltrasound or ultrasonography is a medical imaging technique that uses high frequency
sound waves and their echoes bullBut what is the ultrasound waves
Krautkramer NDT Ultrasonic Systems
Spectrum of sound
Frequency range Hz Description Example
0 - 20 Infrasound Earth quake
20 - 20000 Audible sound Speech music
gt20000 Ultrasound Bat Quartz crystal
Medical ultrasound frequency is 1Mhz-10Mhzوعرضية طولية نوعيين صوتية الفوق الموجات
Krautkramer NDT Ultrasonic Systems
Direction of oscillation
Direction of propagationLongitudinal wave
Sound propagation
Krautkramer NDT Ultrasonic Systems
Direction of propagationTransverse waveDirection of oscillation
Sound propagation
Krautkramer NDT Ultrasonic Systems
Wave propagation
AirWater
Steel longSteel trans
330 ms
1480 ms
3250 ms
5920 ms
Longitudinal waves propagate in all kind of materialsTransverse waves only propagate in solid bodies Due to the different type of oscillation transverse wavestravel at lower speedsSound velocity mainly depends on the density and E-modulus of the material
Difference between EM and soundbull Material through which wave movesbull Medium not required for all wave types
ndash no medium required for electromagnetic wavesbull radiobull x-raysbull infraredbull ultraviolet
ndash medium is required for soundbull sound does not travel through vacuum
Talk louder I canrsquot hear
you
How to produce sound wave
bull By applying voltage on some material face likendash Quartzndash PZT
Krautkramer NDT Ultrasonic Systems
Piezoelectric Effect
Piezoelectrical Crystal (Quartz)
Battery
+
Krautkramer NDT Ultrasonic Systems
+
The crystal gets thicker due to a distortion of the crystal lattice
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
+
The effect inverses with polarity change
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
An alternating voltage generates crystal oscillations at the frequency f
U(f)
Sound wave with
frequency f
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
A short voltage pulse generates an oscillation at the crystallsquos resonantfrequency f0 OPERATING FREQUNCY
Short pulse lt ( 1 micros)
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
How to receive sound waves
A sound wave hitting a piezoelectric crystal induces crystal vibration which then causes electrical voltages at the crystal surfaces
Electrical energy
Piezoelectrical crystal Ultrasonic wave
Krautkramer NDT Ultrasonic Systems
N
Near field Far field
Focus Angle of divergenceCrystalAccoustical axis
D0
6
Sound field
Transducer array
bull Transducer = ARRAY OF PIEZOELECTRICAL ELEMENTS Typically 128 to 512
bull SPECFICATIONndash Materialndash ARRAY LENGHTndash Frequency rang
bull resolutionndash Depth CMndash Type
bull LINEAR ARRAYbull PHASED ARRAY
Ultrasound Display
bull One sound pulse producesndash one image scan line
bull one series of gray shade dots in a line
bull Multiple pulsesndash two dimensional image
obtained by moving direction in which sound transmitted
Real-time Scanning
Each pulse generates one lineExcept for multiple focal zones
one frame consists of many individual scan lines
lines framesPRF (Hz) = ------------ X--------------
frame sec
One pulse = one line
Linear Curved linear array Phased arraysectorEndocavitary Intraoperative
Transducer ArraysbullVirtually all commercial transducers are
arraysndashMultiple small elements in single housing
bullAllows sound beam to be electronicallyndashFocusedndashSteeredndashShaped
Electronic Scanning
bullTransducer ArraysndashMultiple small transducersndashActivated in groups
Electrical ScanningPerformed with transducer arrays
multiple elements inside transducer assembly arranged in either
a line (linear array)
concentric circles (annular array)
Curvilinear Array Linear Array
Linear Array ScanningTwo techniques for activating groups of linear
transducersSwitched Arrays
activate all elements in group at same timePhased Arrays
Activate group elements at slightly different timesimpose timing delays between activations of elements in group
Linear Switched ArraysbullElements energized as groups
ndashgroup acts like one large transducer
bullGroups moved up amp down through elements
ndashsame effect as manually translating
ndashvery fast scanning possible (several times per second)
bullresults in real time image
Linear Switched Arrays
Linear Phased ArraybullGroups of elements energizedndashsame as with switched arraysbullvoltage pulse applied to all
elements of a groupBUT
bullelements not all pulsed at same time
1
2
Linear Phased Arraybulltiming variations allow beam to
be ndashshapedndashsteeredndashfocused
Above arrows indicate timing variations
By activating bottom element first amp top last beam directed upward
Beam steered upward
Linear Phased Array
Above arrows indicate timing variationsBy activating top
element first amp bottom last beam directed
downward
Beam steered downward
By changing timing variations between pulses beam can be scanned from top to bottom
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
US development
What is Ultrasound machine
bullUltrasound or ultrasonography is a medical imaging technique that uses high frequency
sound waves and their echoes bullBut what is the ultrasound waves
Krautkramer NDT Ultrasonic Systems
Spectrum of sound
Frequency range Hz Description Example
0 - 20 Infrasound Earth quake
20 - 20000 Audible sound Speech music
gt20000 Ultrasound Bat Quartz crystal
Medical ultrasound frequency is 1Mhz-10Mhzوعرضية طولية نوعيين صوتية الفوق الموجات
Krautkramer NDT Ultrasonic Systems
Direction of oscillation
Direction of propagationLongitudinal wave
Sound propagation
Krautkramer NDT Ultrasonic Systems
Direction of propagationTransverse waveDirection of oscillation
Sound propagation
Krautkramer NDT Ultrasonic Systems
Wave propagation
AirWater
Steel longSteel trans
330 ms
1480 ms
3250 ms
5920 ms
Longitudinal waves propagate in all kind of materialsTransverse waves only propagate in solid bodies Due to the different type of oscillation transverse wavestravel at lower speedsSound velocity mainly depends on the density and E-modulus of the material
Difference between EM and soundbull Material through which wave movesbull Medium not required for all wave types
ndash no medium required for electromagnetic wavesbull radiobull x-raysbull infraredbull ultraviolet
ndash medium is required for soundbull sound does not travel through vacuum
Talk louder I canrsquot hear
you
How to produce sound wave
bull By applying voltage on some material face likendash Quartzndash PZT
Krautkramer NDT Ultrasonic Systems
Piezoelectric Effect
Piezoelectrical Crystal (Quartz)
Battery
+
Krautkramer NDT Ultrasonic Systems
+
The crystal gets thicker due to a distortion of the crystal lattice
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
+
The effect inverses with polarity change
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
An alternating voltage generates crystal oscillations at the frequency f
U(f)
Sound wave with
frequency f
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
A short voltage pulse generates an oscillation at the crystallsquos resonantfrequency f0 OPERATING FREQUNCY
Short pulse lt ( 1 micros)
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
How to receive sound waves
A sound wave hitting a piezoelectric crystal induces crystal vibration which then causes electrical voltages at the crystal surfaces
Electrical energy
Piezoelectrical crystal Ultrasonic wave
Krautkramer NDT Ultrasonic Systems
N
Near field Far field
Focus Angle of divergenceCrystalAccoustical axis
D0
6
Sound field
Transducer array
bull Transducer = ARRAY OF PIEZOELECTRICAL ELEMENTS Typically 128 to 512
bull SPECFICATIONndash Materialndash ARRAY LENGHTndash Frequency rang
bull resolutionndash Depth CMndash Type
bull LINEAR ARRAYbull PHASED ARRAY
Ultrasound Display
bull One sound pulse producesndash one image scan line
bull one series of gray shade dots in a line
bull Multiple pulsesndash two dimensional image
obtained by moving direction in which sound transmitted
Real-time Scanning
Each pulse generates one lineExcept for multiple focal zones
one frame consists of many individual scan lines
lines framesPRF (Hz) = ------------ X--------------
frame sec
One pulse = one line
Linear Curved linear array Phased arraysectorEndocavitary Intraoperative
Transducer ArraysbullVirtually all commercial transducers are
arraysndashMultiple small elements in single housing
bullAllows sound beam to be electronicallyndashFocusedndashSteeredndashShaped
Electronic Scanning
bullTransducer ArraysndashMultiple small transducersndashActivated in groups
Electrical ScanningPerformed with transducer arrays
multiple elements inside transducer assembly arranged in either
a line (linear array)
concentric circles (annular array)
Curvilinear Array Linear Array
Linear Array ScanningTwo techniques for activating groups of linear
transducersSwitched Arrays
activate all elements in group at same timePhased Arrays
Activate group elements at slightly different timesimpose timing delays between activations of elements in group
Linear Switched ArraysbullElements energized as groups
ndashgroup acts like one large transducer
bullGroups moved up amp down through elements
ndashsame effect as manually translating
ndashvery fast scanning possible (several times per second)
bullresults in real time image
Linear Switched Arrays
Linear Phased ArraybullGroups of elements energizedndashsame as with switched arraysbullvoltage pulse applied to all
elements of a groupBUT
bullelements not all pulsed at same time
1
2
Linear Phased Arraybulltiming variations allow beam to
be ndashshapedndashsteeredndashfocused
Above arrows indicate timing variations
By activating bottom element first amp top last beam directed upward
Beam steered upward
Linear Phased Array
Above arrows indicate timing variationsBy activating top
element first amp bottom last beam directed
downward
Beam steered downward
By changing timing variations between pulses beam can be scanned from top to bottom
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
What is Ultrasound machine
bullUltrasound or ultrasonography is a medical imaging technique that uses high frequency
sound waves and their echoes bullBut what is the ultrasound waves
Krautkramer NDT Ultrasonic Systems
Spectrum of sound
Frequency range Hz Description Example
0 - 20 Infrasound Earth quake
20 - 20000 Audible sound Speech music
gt20000 Ultrasound Bat Quartz crystal
Medical ultrasound frequency is 1Mhz-10Mhzوعرضية طولية نوعيين صوتية الفوق الموجات
Krautkramer NDT Ultrasonic Systems
Direction of oscillation
Direction of propagationLongitudinal wave
Sound propagation
Krautkramer NDT Ultrasonic Systems
Direction of propagationTransverse waveDirection of oscillation
Sound propagation
Krautkramer NDT Ultrasonic Systems
Wave propagation
AirWater
Steel longSteel trans
330 ms
1480 ms
3250 ms
5920 ms
Longitudinal waves propagate in all kind of materialsTransverse waves only propagate in solid bodies Due to the different type of oscillation transverse wavestravel at lower speedsSound velocity mainly depends on the density and E-modulus of the material
Difference between EM and soundbull Material through which wave movesbull Medium not required for all wave types
ndash no medium required for electromagnetic wavesbull radiobull x-raysbull infraredbull ultraviolet
ndash medium is required for soundbull sound does not travel through vacuum
Talk louder I canrsquot hear
you
How to produce sound wave
bull By applying voltage on some material face likendash Quartzndash PZT
Krautkramer NDT Ultrasonic Systems
Piezoelectric Effect
Piezoelectrical Crystal (Quartz)
Battery
+
Krautkramer NDT Ultrasonic Systems
+
The crystal gets thicker due to a distortion of the crystal lattice
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
+
The effect inverses with polarity change
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
An alternating voltage generates crystal oscillations at the frequency f
U(f)
Sound wave with
frequency f
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
A short voltage pulse generates an oscillation at the crystallsquos resonantfrequency f0 OPERATING FREQUNCY
Short pulse lt ( 1 micros)
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
How to receive sound waves
A sound wave hitting a piezoelectric crystal induces crystal vibration which then causes electrical voltages at the crystal surfaces
Electrical energy
Piezoelectrical crystal Ultrasonic wave
Krautkramer NDT Ultrasonic Systems
N
Near field Far field
Focus Angle of divergenceCrystalAccoustical axis
D0
6
Sound field
Transducer array
bull Transducer = ARRAY OF PIEZOELECTRICAL ELEMENTS Typically 128 to 512
bull SPECFICATIONndash Materialndash ARRAY LENGHTndash Frequency rang
bull resolutionndash Depth CMndash Type
bull LINEAR ARRAYbull PHASED ARRAY
Ultrasound Display
bull One sound pulse producesndash one image scan line
bull one series of gray shade dots in a line
bull Multiple pulsesndash two dimensional image
obtained by moving direction in which sound transmitted
Real-time Scanning
Each pulse generates one lineExcept for multiple focal zones
one frame consists of many individual scan lines
lines framesPRF (Hz) = ------------ X--------------
frame sec
One pulse = one line
Linear Curved linear array Phased arraysectorEndocavitary Intraoperative
Transducer ArraysbullVirtually all commercial transducers are
arraysndashMultiple small elements in single housing
bullAllows sound beam to be electronicallyndashFocusedndashSteeredndashShaped
Electronic Scanning
bullTransducer ArraysndashMultiple small transducersndashActivated in groups
Electrical ScanningPerformed with transducer arrays
multiple elements inside transducer assembly arranged in either
a line (linear array)
concentric circles (annular array)
Curvilinear Array Linear Array
Linear Array ScanningTwo techniques for activating groups of linear
transducersSwitched Arrays
activate all elements in group at same timePhased Arrays
Activate group elements at slightly different timesimpose timing delays between activations of elements in group
Linear Switched ArraysbullElements energized as groups
ndashgroup acts like one large transducer
bullGroups moved up amp down through elements
ndashsame effect as manually translating
ndashvery fast scanning possible (several times per second)
bullresults in real time image
Linear Switched Arrays
Linear Phased ArraybullGroups of elements energizedndashsame as with switched arraysbullvoltage pulse applied to all
elements of a groupBUT
bullelements not all pulsed at same time
1
2
Linear Phased Arraybulltiming variations allow beam to
be ndashshapedndashsteeredndashfocused
Above arrows indicate timing variations
By activating bottom element first amp top last beam directed upward
Beam steered upward
Linear Phased Array
Above arrows indicate timing variationsBy activating top
element first amp bottom last beam directed
downward
Beam steered downward
By changing timing variations between pulses beam can be scanned from top to bottom
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Krautkramer NDT Ultrasonic Systems
Spectrum of sound
Frequency range Hz Description Example
0 - 20 Infrasound Earth quake
20 - 20000 Audible sound Speech music
gt20000 Ultrasound Bat Quartz crystal
Medical ultrasound frequency is 1Mhz-10Mhzوعرضية طولية نوعيين صوتية الفوق الموجات
Krautkramer NDT Ultrasonic Systems
Direction of oscillation
Direction of propagationLongitudinal wave
Sound propagation
Krautkramer NDT Ultrasonic Systems
Direction of propagationTransverse waveDirection of oscillation
Sound propagation
Krautkramer NDT Ultrasonic Systems
Wave propagation
AirWater
Steel longSteel trans
330 ms
1480 ms
3250 ms
5920 ms
Longitudinal waves propagate in all kind of materialsTransverse waves only propagate in solid bodies Due to the different type of oscillation transverse wavestravel at lower speedsSound velocity mainly depends on the density and E-modulus of the material
Difference between EM and soundbull Material through which wave movesbull Medium not required for all wave types
ndash no medium required for electromagnetic wavesbull radiobull x-raysbull infraredbull ultraviolet
ndash medium is required for soundbull sound does not travel through vacuum
Talk louder I canrsquot hear
you
How to produce sound wave
bull By applying voltage on some material face likendash Quartzndash PZT
Krautkramer NDT Ultrasonic Systems
Piezoelectric Effect
Piezoelectrical Crystal (Quartz)
Battery
+
Krautkramer NDT Ultrasonic Systems
+
The crystal gets thicker due to a distortion of the crystal lattice
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
+
The effect inverses with polarity change
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
An alternating voltage generates crystal oscillations at the frequency f
U(f)
Sound wave with
frequency f
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
A short voltage pulse generates an oscillation at the crystallsquos resonantfrequency f0 OPERATING FREQUNCY
Short pulse lt ( 1 micros)
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
How to receive sound waves
A sound wave hitting a piezoelectric crystal induces crystal vibration which then causes electrical voltages at the crystal surfaces
Electrical energy
Piezoelectrical crystal Ultrasonic wave
Krautkramer NDT Ultrasonic Systems
N
Near field Far field
Focus Angle of divergenceCrystalAccoustical axis
D0
6
Sound field
Transducer array
bull Transducer = ARRAY OF PIEZOELECTRICAL ELEMENTS Typically 128 to 512
bull SPECFICATIONndash Materialndash ARRAY LENGHTndash Frequency rang
bull resolutionndash Depth CMndash Type
bull LINEAR ARRAYbull PHASED ARRAY
Ultrasound Display
bull One sound pulse producesndash one image scan line
bull one series of gray shade dots in a line
bull Multiple pulsesndash two dimensional image
obtained by moving direction in which sound transmitted
Real-time Scanning
Each pulse generates one lineExcept for multiple focal zones
one frame consists of many individual scan lines
lines framesPRF (Hz) = ------------ X--------------
frame sec
One pulse = one line
Linear Curved linear array Phased arraysectorEndocavitary Intraoperative
Transducer ArraysbullVirtually all commercial transducers are
arraysndashMultiple small elements in single housing
bullAllows sound beam to be electronicallyndashFocusedndashSteeredndashShaped
Electronic Scanning
bullTransducer ArraysndashMultiple small transducersndashActivated in groups
Electrical ScanningPerformed with transducer arrays
multiple elements inside transducer assembly arranged in either
a line (linear array)
concentric circles (annular array)
Curvilinear Array Linear Array
Linear Array ScanningTwo techniques for activating groups of linear
transducersSwitched Arrays
activate all elements in group at same timePhased Arrays
Activate group elements at slightly different timesimpose timing delays between activations of elements in group
Linear Switched ArraysbullElements energized as groups
ndashgroup acts like one large transducer
bullGroups moved up amp down through elements
ndashsame effect as manually translating
ndashvery fast scanning possible (several times per second)
bullresults in real time image
Linear Switched Arrays
Linear Phased ArraybullGroups of elements energizedndashsame as with switched arraysbullvoltage pulse applied to all
elements of a groupBUT
bullelements not all pulsed at same time
1
2
Linear Phased Arraybulltiming variations allow beam to
be ndashshapedndashsteeredndashfocused
Above arrows indicate timing variations
By activating bottom element first amp top last beam directed upward
Beam steered upward
Linear Phased Array
Above arrows indicate timing variationsBy activating top
element first amp bottom last beam directed
downward
Beam steered downward
By changing timing variations between pulses beam can be scanned from top to bottom
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Krautkramer NDT Ultrasonic Systems
Direction of oscillation
Direction of propagationLongitudinal wave
Sound propagation
Krautkramer NDT Ultrasonic Systems
Direction of propagationTransverse waveDirection of oscillation
Sound propagation
Krautkramer NDT Ultrasonic Systems
Wave propagation
AirWater
Steel longSteel trans
330 ms
1480 ms
3250 ms
5920 ms
Longitudinal waves propagate in all kind of materialsTransverse waves only propagate in solid bodies Due to the different type of oscillation transverse wavestravel at lower speedsSound velocity mainly depends on the density and E-modulus of the material
Difference between EM and soundbull Material through which wave movesbull Medium not required for all wave types
ndash no medium required for electromagnetic wavesbull radiobull x-raysbull infraredbull ultraviolet
ndash medium is required for soundbull sound does not travel through vacuum
Talk louder I canrsquot hear
you
How to produce sound wave
bull By applying voltage on some material face likendash Quartzndash PZT
Krautkramer NDT Ultrasonic Systems
Piezoelectric Effect
Piezoelectrical Crystal (Quartz)
Battery
+
Krautkramer NDT Ultrasonic Systems
+
The crystal gets thicker due to a distortion of the crystal lattice
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
+
The effect inverses with polarity change
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
An alternating voltage generates crystal oscillations at the frequency f
U(f)
Sound wave with
frequency f
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
A short voltage pulse generates an oscillation at the crystallsquos resonantfrequency f0 OPERATING FREQUNCY
Short pulse lt ( 1 micros)
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
How to receive sound waves
A sound wave hitting a piezoelectric crystal induces crystal vibration which then causes electrical voltages at the crystal surfaces
Electrical energy
Piezoelectrical crystal Ultrasonic wave
Krautkramer NDT Ultrasonic Systems
N
Near field Far field
Focus Angle of divergenceCrystalAccoustical axis
D0
6
Sound field
Transducer array
bull Transducer = ARRAY OF PIEZOELECTRICAL ELEMENTS Typically 128 to 512
bull SPECFICATIONndash Materialndash ARRAY LENGHTndash Frequency rang
bull resolutionndash Depth CMndash Type
bull LINEAR ARRAYbull PHASED ARRAY
Ultrasound Display
bull One sound pulse producesndash one image scan line
bull one series of gray shade dots in a line
bull Multiple pulsesndash two dimensional image
obtained by moving direction in which sound transmitted
Real-time Scanning
Each pulse generates one lineExcept for multiple focal zones
one frame consists of many individual scan lines
lines framesPRF (Hz) = ------------ X--------------
frame sec
One pulse = one line
Linear Curved linear array Phased arraysectorEndocavitary Intraoperative
Transducer ArraysbullVirtually all commercial transducers are
arraysndashMultiple small elements in single housing
bullAllows sound beam to be electronicallyndashFocusedndashSteeredndashShaped
Electronic Scanning
bullTransducer ArraysndashMultiple small transducersndashActivated in groups
Electrical ScanningPerformed with transducer arrays
multiple elements inside transducer assembly arranged in either
a line (linear array)
concentric circles (annular array)
Curvilinear Array Linear Array
Linear Array ScanningTwo techniques for activating groups of linear
transducersSwitched Arrays
activate all elements in group at same timePhased Arrays
Activate group elements at slightly different timesimpose timing delays between activations of elements in group
Linear Switched ArraysbullElements energized as groups
ndashgroup acts like one large transducer
bullGroups moved up amp down through elements
ndashsame effect as manually translating
ndashvery fast scanning possible (several times per second)
bullresults in real time image
Linear Switched Arrays
Linear Phased ArraybullGroups of elements energizedndashsame as with switched arraysbullvoltage pulse applied to all
elements of a groupBUT
bullelements not all pulsed at same time
1
2
Linear Phased Arraybulltiming variations allow beam to
be ndashshapedndashsteeredndashfocused
Above arrows indicate timing variations
By activating bottom element first amp top last beam directed upward
Beam steered upward
Linear Phased Array
Above arrows indicate timing variationsBy activating top
element first amp bottom last beam directed
downward
Beam steered downward
By changing timing variations between pulses beam can be scanned from top to bottom
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Krautkramer NDT Ultrasonic Systems
Direction of propagationTransverse waveDirection of oscillation
Sound propagation
Krautkramer NDT Ultrasonic Systems
Wave propagation
AirWater
Steel longSteel trans
330 ms
1480 ms
3250 ms
5920 ms
Longitudinal waves propagate in all kind of materialsTransverse waves only propagate in solid bodies Due to the different type of oscillation transverse wavestravel at lower speedsSound velocity mainly depends on the density and E-modulus of the material
Difference between EM and soundbull Material through which wave movesbull Medium not required for all wave types
ndash no medium required for electromagnetic wavesbull radiobull x-raysbull infraredbull ultraviolet
ndash medium is required for soundbull sound does not travel through vacuum
Talk louder I canrsquot hear
you
How to produce sound wave
bull By applying voltage on some material face likendash Quartzndash PZT
Krautkramer NDT Ultrasonic Systems
Piezoelectric Effect
Piezoelectrical Crystal (Quartz)
Battery
+
Krautkramer NDT Ultrasonic Systems
+
The crystal gets thicker due to a distortion of the crystal lattice
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
+
The effect inverses with polarity change
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
An alternating voltage generates crystal oscillations at the frequency f
U(f)
Sound wave with
frequency f
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
A short voltage pulse generates an oscillation at the crystallsquos resonantfrequency f0 OPERATING FREQUNCY
Short pulse lt ( 1 micros)
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
How to receive sound waves
A sound wave hitting a piezoelectric crystal induces crystal vibration which then causes electrical voltages at the crystal surfaces
Electrical energy
Piezoelectrical crystal Ultrasonic wave
Krautkramer NDT Ultrasonic Systems
N
Near field Far field
Focus Angle of divergenceCrystalAccoustical axis
D0
6
Sound field
Transducer array
bull Transducer = ARRAY OF PIEZOELECTRICAL ELEMENTS Typically 128 to 512
bull SPECFICATIONndash Materialndash ARRAY LENGHTndash Frequency rang
bull resolutionndash Depth CMndash Type
bull LINEAR ARRAYbull PHASED ARRAY
Ultrasound Display
bull One sound pulse producesndash one image scan line
bull one series of gray shade dots in a line
bull Multiple pulsesndash two dimensional image
obtained by moving direction in which sound transmitted
Real-time Scanning
Each pulse generates one lineExcept for multiple focal zones
one frame consists of many individual scan lines
lines framesPRF (Hz) = ------------ X--------------
frame sec
One pulse = one line
Linear Curved linear array Phased arraysectorEndocavitary Intraoperative
Transducer ArraysbullVirtually all commercial transducers are
arraysndashMultiple small elements in single housing
bullAllows sound beam to be electronicallyndashFocusedndashSteeredndashShaped
Electronic Scanning
bullTransducer ArraysndashMultiple small transducersndashActivated in groups
Electrical ScanningPerformed with transducer arrays
multiple elements inside transducer assembly arranged in either
a line (linear array)
concentric circles (annular array)
Curvilinear Array Linear Array
Linear Array ScanningTwo techniques for activating groups of linear
transducersSwitched Arrays
activate all elements in group at same timePhased Arrays
Activate group elements at slightly different timesimpose timing delays between activations of elements in group
Linear Switched ArraysbullElements energized as groups
ndashgroup acts like one large transducer
bullGroups moved up amp down through elements
ndashsame effect as manually translating
ndashvery fast scanning possible (several times per second)
bullresults in real time image
Linear Switched Arrays
Linear Phased ArraybullGroups of elements energizedndashsame as with switched arraysbullvoltage pulse applied to all
elements of a groupBUT
bullelements not all pulsed at same time
1
2
Linear Phased Arraybulltiming variations allow beam to
be ndashshapedndashsteeredndashfocused
Above arrows indicate timing variations
By activating bottom element first amp top last beam directed upward
Beam steered upward
Linear Phased Array
Above arrows indicate timing variationsBy activating top
element first amp bottom last beam directed
downward
Beam steered downward
By changing timing variations between pulses beam can be scanned from top to bottom
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Krautkramer NDT Ultrasonic Systems
Wave propagation
AirWater
Steel longSteel trans
330 ms
1480 ms
3250 ms
5920 ms
Longitudinal waves propagate in all kind of materialsTransverse waves only propagate in solid bodies Due to the different type of oscillation transverse wavestravel at lower speedsSound velocity mainly depends on the density and E-modulus of the material
Difference between EM and soundbull Material through which wave movesbull Medium not required for all wave types
ndash no medium required for electromagnetic wavesbull radiobull x-raysbull infraredbull ultraviolet
ndash medium is required for soundbull sound does not travel through vacuum
Talk louder I canrsquot hear
you
How to produce sound wave
bull By applying voltage on some material face likendash Quartzndash PZT
Krautkramer NDT Ultrasonic Systems
Piezoelectric Effect
Piezoelectrical Crystal (Quartz)
Battery
+
Krautkramer NDT Ultrasonic Systems
+
The crystal gets thicker due to a distortion of the crystal lattice
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
+
The effect inverses with polarity change
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
An alternating voltage generates crystal oscillations at the frequency f
U(f)
Sound wave with
frequency f
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
A short voltage pulse generates an oscillation at the crystallsquos resonantfrequency f0 OPERATING FREQUNCY
Short pulse lt ( 1 micros)
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
How to receive sound waves
A sound wave hitting a piezoelectric crystal induces crystal vibration which then causes electrical voltages at the crystal surfaces
Electrical energy
Piezoelectrical crystal Ultrasonic wave
Krautkramer NDT Ultrasonic Systems
N
Near field Far field
Focus Angle of divergenceCrystalAccoustical axis
D0
6
Sound field
Transducer array
bull Transducer = ARRAY OF PIEZOELECTRICAL ELEMENTS Typically 128 to 512
bull SPECFICATIONndash Materialndash ARRAY LENGHTndash Frequency rang
bull resolutionndash Depth CMndash Type
bull LINEAR ARRAYbull PHASED ARRAY
Ultrasound Display
bull One sound pulse producesndash one image scan line
bull one series of gray shade dots in a line
bull Multiple pulsesndash two dimensional image
obtained by moving direction in which sound transmitted
Real-time Scanning
Each pulse generates one lineExcept for multiple focal zones
one frame consists of many individual scan lines
lines framesPRF (Hz) = ------------ X--------------
frame sec
One pulse = one line
Linear Curved linear array Phased arraysectorEndocavitary Intraoperative
Transducer ArraysbullVirtually all commercial transducers are
arraysndashMultiple small elements in single housing
bullAllows sound beam to be electronicallyndashFocusedndashSteeredndashShaped
Electronic Scanning
bullTransducer ArraysndashMultiple small transducersndashActivated in groups
Electrical ScanningPerformed with transducer arrays
multiple elements inside transducer assembly arranged in either
a line (linear array)
concentric circles (annular array)
Curvilinear Array Linear Array
Linear Array ScanningTwo techniques for activating groups of linear
transducersSwitched Arrays
activate all elements in group at same timePhased Arrays
Activate group elements at slightly different timesimpose timing delays between activations of elements in group
Linear Switched ArraysbullElements energized as groups
ndashgroup acts like one large transducer
bullGroups moved up amp down through elements
ndashsame effect as manually translating
ndashvery fast scanning possible (several times per second)
bullresults in real time image
Linear Switched Arrays
Linear Phased ArraybullGroups of elements energizedndashsame as with switched arraysbullvoltage pulse applied to all
elements of a groupBUT
bullelements not all pulsed at same time
1
2
Linear Phased Arraybulltiming variations allow beam to
be ndashshapedndashsteeredndashfocused
Above arrows indicate timing variations
By activating bottom element first amp top last beam directed upward
Beam steered upward
Linear Phased Array
Above arrows indicate timing variationsBy activating top
element first amp bottom last beam directed
downward
Beam steered downward
By changing timing variations between pulses beam can be scanned from top to bottom
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Difference between EM and soundbull Material through which wave movesbull Medium not required for all wave types
ndash no medium required for electromagnetic wavesbull radiobull x-raysbull infraredbull ultraviolet
ndash medium is required for soundbull sound does not travel through vacuum
Talk louder I canrsquot hear
you
How to produce sound wave
bull By applying voltage on some material face likendash Quartzndash PZT
Krautkramer NDT Ultrasonic Systems
Piezoelectric Effect
Piezoelectrical Crystal (Quartz)
Battery
+
Krautkramer NDT Ultrasonic Systems
+
The crystal gets thicker due to a distortion of the crystal lattice
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
+
The effect inverses with polarity change
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
An alternating voltage generates crystal oscillations at the frequency f
U(f)
Sound wave with
frequency f
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
A short voltage pulse generates an oscillation at the crystallsquos resonantfrequency f0 OPERATING FREQUNCY
Short pulse lt ( 1 micros)
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
How to receive sound waves
A sound wave hitting a piezoelectric crystal induces crystal vibration which then causes electrical voltages at the crystal surfaces
Electrical energy
Piezoelectrical crystal Ultrasonic wave
Krautkramer NDT Ultrasonic Systems
N
Near field Far field
Focus Angle of divergenceCrystalAccoustical axis
D0
6
Sound field
Transducer array
bull Transducer = ARRAY OF PIEZOELECTRICAL ELEMENTS Typically 128 to 512
bull SPECFICATIONndash Materialndash ARRAY LENGHTndash Frequency rang
bull resolutionndash Depth CMndash Type
bull LINEAR ARRAYbull PHASED ARRAY
Ultrasound Display
bull One sound pulse producesndash one image scan line
bull one series of gray shade dots in a line
bull Multiple pulsesndash two dimensional image
obtained by moving direction in which sound transmitted
Real-time Scanning
Each pulse generates one lineExcept for multiple focal zones
one frame consists of many individual scan lines
lines framesPRF (Hz) = ------------ X--------------
frame sec
One pulse = one line
Linear Curved linear array Phased arraysectorEndocavitary Intraoperative
Transducer ArraysbullVirtually all commercial transducers are
arraysndashMultiple small elements in single housing
bullAllows sound beam to be electronicallyndashFocusedndashSteeredndashShaped
Electronic Scanning
bullTransducer ArraysndashMultiple small transducersndashActivated in groups
Electrical ScanningPerformed with transducer arrays
multiple elements inside transducer assembly arranged in either
a line (linear array)
concentric circles (annular array)
Curvilinear Array Linear Array
Linear Array ScanningTwo techniques for activating groups of linear
transducersSwitched Arrays
activate all elements in group at same timePhased Arrays
Activate group elements at slightly different timesimpose timing delays between activations of elements in group
Linear Switched ArraysbullElements energized as groups
ndashgroup acts like one large transducer
bullGroups moved up amp down through elements
ndashsame effect as manually translating
ndashvery fast scanning possible (several times per second)
bullresults in real time image
Linear Switched Arrays
Linear Phased ArraybullGroups of elements energizedndashsame as with switched arraysbullvoltage pulse applied to all
elements of a groupBUT
bullelements not all pulsed at same time
1
2
Linear Phased Arraybulltiming variations allow beam to
be ndashshapedndashsteeredndashfocused
Above arrows indicate timing variations
By activating bottom element first amp top last beam directed upward
Beam steered upward
Linear Phased Array
Above arrows indicate timing variationsBy activating top
element first amp bottom last beam directed
downward
Beam steered downward
By changing timing variations between pulses beam can be scanned from top to bottom
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
How to produce sound wave
bull By applying voltage on some material face likendash Quartzndash PZT
Krautkramer NDT Ultrasonic Systems
Piezoelectric Effect
Piezoelectrical Crystal (Quartz)
Battery
+
Krautkramer NDT Ultrasonic Systems
+
The crystal gets thicker due to a distortion of the crystal lattice
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
+
The effect inverses with polarity change
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
An alternating voltage generates crystal oscillations at the frequency f
U(f)
Sound wave with
frequency f
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
A short voltage pulse generates an oscillation at the crystallsquos resonantfrequency f0 OPERATING FREQUNCY
Short pulse lt ( 1 micros)
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
How to receive sound waves
A sound wave hitting a piezoelectric crystal induces crystal vibration which then causes electrical voltages at the crystal surfaces
Electrical energy
Piezoelectrical crystal Ultrasonic wave
Krautkramer NDT Ultrasonic Systems
N
Near field Far field
Focus Angle of divergenceCrystalAccoustical axis
D0
6
Sound field
Transducer array
bull Transducer = ARRAY OF PIEZOELECTRICAL ELEMENTS Typically 128 to 512
bull SPECFICATIONndash Materialndash ARRAY LENGHTndash Frequency rang
bull resolutionndash Depth CMndash Type
bull LINEAR ARRAYbull PHASED ARRAY
Ultrasound Display
bull One sound pulse producesndash one image scan line
bull one series of gray shade dots in a line
bull Multiple pulsesndash two dimensional image
obtained by moving direction in which sound transmitted
Real-time Scanning
Each pulse generates one lineExcept for multiple focal zones
one frame consists of many individual scan lines
lines framesPRF (Hz) = ------------ X--------------
frame sec
One pulse = one line
Linear Curved linear array Phased arraysectorEndocavitary Intraoperative
Transducer ArraysbullVirtually all commercial transducers are
arraysndashMultiple small elements in single housing
bullAllows sound beam to be electronicallyndashFocusedndashSteeredndashShaped
Electronic Scanning
bullTransducer ArraysndashMultiple small transducersndashActivated in groups
Electrical ScanningPerformed with transducer arrays
multiple elements inside transducer assembly arranged in either
a line (linear array)
concentric circles (annular array)
Curvilinear Array Linear Array
Linear Array ScanningTwo techniques for activating groups of linear
transducersSwitched Arrays
activate all elements in group at same timePhased Arrays
Activate group elements at slightly different timesimpose timing delays between activations of elements in group
Linear Switched ArraysbullElements energized as groups
ndashgroup acts like one large transducer
bullGroups moved up amp down through elements
ndashsame effect as manually translating
ndashvery fast scanning possible (several times per second)
bullresults in real time image
Linear Switched Arrays
Linear Phased ArraybullGroups of elements energizedndashsame as with switched arraysbullvoltage pulse applied to all
elements of a groupBUT
bullelements not all pulsed at same time
1
2
Linear Phased Arraybulltiming variations allow beam to
be ndashshapedndashsteeredndashfocused
Above arrows indicate timing variations
By activating bottom element first amp top last beam directed upward
Beam steered upward
Linear Phased Array
Above arrows indicate timing variationsBy activating top
element first amp bottom last beam directed
downward
Beam steered downward
By changing timing variations between pulses beam can be scanned from top to bottom
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Krautkramer NDT Ultrasonic Systems
Piezoelectric Effect
Piezoelectrical Crystal (Quartz)
Battery
+
Krautkramer NDT Ultrasonic Systems
+
The crystal gets thicker due to a distortion of the crystal lattice
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
+
The effect inverses with polarity change
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
An alternating voltage generates crystal oscillations at the frequency f
U(f)
Sound wave with
frequency f
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
A short voltage pulse generates an oscillation at the crystallsquos resonantfrequency f0 OPERATING FREQUNCY
Short pulse lt ( 1 micros)
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
How to receive sound waves
A sound wave hitting a piezoelectric crystal induces crystal vibration which then causes electrical voltages at the crystal surfaces
Electrical energy
Piezoelectrical crystal Ultrasonic wave
Krautkramer NDT Ultrasonic Systems
N
Near field Far field
Focus Angle of divergenceCrystalAccoustical axis
D0
6
Sound field
Transducer array
bull Transducer = ARRAY OF PIEZOELECTRICAL ELEMENTS Typically 128 to 512
bull SPECFICATIONndash Materialndash ARRAY LENGHTndash Frequency rang
bull resolutionndash Depth CMndash Type
bull LINEAR ARRAYbull PHASED ARRAY
Ultrasound Display
bull One sound pulse producesndash one image scan line
bull one series of gray shade dots in a line
bull Multiple pulsesndash two dimensional image
obtained by moving direction in which sound transmitted
Real-time Scanning
Each pulse generates one lineExcept for multiple focal zones
one frame consists of many individual scan lines
lines framesPRF (Hz) = ------------ X--------------
frame sec
One pulse = one line
Linear Curved linear array Phased arraysectorEndocavitary Intraoperative
Transducer ArraysbullVirtually all commercial transducers are
arraysndashMultiple small elements in single housing
bullAllows sound beam to be electronicallyndashFocusedndashSteeredndashShaped
Electronic Scanning
bullTransducer ArraysndashMultiple small transducersndashActivated in groups
Electrical ScanningPerformed with transducer arrays
multiple elements inside transducer assembly arranged in either
a line (linear array)
concentric circles (annular array)
Curvilinear Array Linear Array
Linear Array ScanningTwo techniques for activating groups of linear
transducersSwitched Arrays
activate all elements in group at same timePhased Arrays
Activate group elements at slightly different timesimpose timing delays between activations of elements in group
Linear Switched ArraysbullElements energized as groups
ndashgroup acts like one large transducer
bullGroups moved up amp down through elements
ndashsame effect as manually translating
ndashvery fast scanning possible (several times per second)
bullresults in real time image
Linear Switched Arrays
Linear Phased ArraybullGroups of elements energizedndashsame as with switched arraysbullvoltage pulse applied to all
elements of a groupBUT
bullelements not all pulsed at same time
1
2
Linear Phased Arraybulltiming variations allow beam to
be ndashshapedndashsteeredndashfocused
Above arrows indicate timing variations
By activating bottom element first amp top last beam directed upward
Beam steered upward
Linear Phased Array
Above arrows indicate timing variationsBy activating top
element first amp bottom last beam directed
downward
Beam steered downward
By changing timing variations between pulses beam can be scanned from top to bottom
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Krautkramer NDT Ultrasonic Systems
+
The crystal gets thicker due to a distortion of the crystal lattice
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
+
The effect inverses with polarity change
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
An alternating voltage generates crystal oscillations at the frequency f
U(f)
Sound wave with
frequency f
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
A short voltage pulse generates an oscillation at the crystallsquos resonantfrequency f0 OPERATING FREQUNCY
Short pulse lt ( 1 micros)
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
How to receive sound waves
A sound wave hitting a piezoelectric crystal induces crystal vibration which then causes electrical voltages at the crystal surfaces
Electrical energy
Piezoelectrical crystal Ultrasonic wave
Krautkramer NDT Ultrasonic Systems
N
Near field Far field
Focus Angle of divergenceCrystalAccoustical axis
D0
6
Sound field
Transducer array
bull Transducer = ARRAY OF PIEZOELECTRICAL ELEMENTS Typically 128 to 512
bull SPECFICATIONndash Materialndash ARRAY LENGHTndash Frequency rang
bull resolutionndash Depth CMndash Type
bull LINEAR ARRAYbull PHASED ARRAY
Ultrasound Display
bull One sound pulse producesndash one image scan line
bull one series of gray shade dots in a line
bull Multiple pulsesndash two dimensional image
obtained by moving direction in which sound transmitted
Real-time Scanning
Each pulse generates one lineExcept for multiple focal zones
one frame consists of many individual scan lines
lines framesPRF (Hz) = ------------ X--------------
frame sec
One pulse = one line
Linear Curved linear array Phased arraysectorEndocavitary Intraoperative
Transducer ArraysbullVirtually all commercial transducers are
arraysndashMultiple small elements in single housing
bullAllows sound beam to be electronicallyndashFocusedndashSteeredndashShaped
Electronic Scanning
bullTransducer ArraysndashMultiple small transducersndashActivated in groups
Electrical ScanningPerformed with transducer arrays
multiple elements inside transducer assembly arranged in either
a line (linear array)
concentric circles (annular array)
Curvilinear Array Linear Array
Linear Array ScanningTwo techniques for activating groups of linear
transducersSwitched Arrays
activate all elements in group at same timePhased Arrays
Activate group elements at slightly different timesimpose timing delays between activations of elements in group
Linear Switched ArraysbullElements energized as groups
ndashgroup acts like one large transducer
bullGroups moved up amp down through elements
ndashsame effect as manually translating
ndashvery fast scanning possible (several times per second)
bullresults in real time image
Linear Switched Arrays
Linear Phased ArraybullGroups of elements energizedndashsame as with switched arraysbullvoltage pulse applied to all
elements of a groupBUT
bullelements not all pulsed at same time
1
2
Linear Phased Arraybulltiming variations allow beam to
be ndashshapedndashsteeredndashfocused
Above arrows indicate timing variations
By activating bottom element first amp top last beam directed upward
Beam steered upward
Linear Phased Array
Above arrows indicate timing variationsBy activating top
element first amp bottom last beam directed
downward
Beam steered downward
By changing timing variations between pulses beam can be scanned from top to bottom
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Krautkramer NDT Ultrasonic Systems
+
The effect inverses with polarity change
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
An alternating voltage generates crystal oscillations at the frequency f
U(f)
Sound wave with
frequency f
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
A short voltage pulse generates an oscillation at the crystallsquos resonantfrequency f0 OPERATING FREQUNCY
Short pulse lt ( 1 micros)
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
How to receive sound waves
A sound wave hitting a piezoelectric crystal induces crystal vibration which then causes electrical voltages at the crystal surfaces
Electrical energy
Piezoelectrical crystal Ultrasonic wave
Krautkramer NDT Ultrasonic Systems
N
Near field Far field
Focus Angle of divergenceCrystalAccoustical axis
D0
6
Sound field
Transducer array
bull Transducer = ARRAY OF PIEZOELECTRICAL ELEMENTS Typically 128 to 512
bull SPECFICATIONndash Materialndash ARRAY LENGHTndash Frequency rang
bull resolutionndash Depth CMndash Type
bull LINEAR ARRAYbull PHASED ARRAY
Ultrasound Display
bull One sound pulse producesndash one image scan line
bull one series of gray shade dots in a line
bull Multiple pulsesndash two dimensional image
obtained by moving direction in which sound transmitted
Real-time Scanning
Each pulse generates one lineExcept for multiple focal zones
one frame consists of many individual scan lines
lines framesPRF (Hz) = ------------ X--------------
frame sec
One pulse = one line
Linear Curved linear array Phased arraysectorEndocavitary Intraoperative
Transducer ArraysbullVirtually all commercial transducers are
arraysndashMultiple small elements in single housing
bullAllows sound beam to be electronicallyndashFocusedndashSteeredndashShaped
Electronic Scanning
bullTransducer ArraysndashMultiple small transducersndashActivated in groups
Electrical ScanningPerformed with transducer arrays
multiple elements inside transducer assembly arranged in either
a line (linear array)
concentric circles (annular array)
Curvilinear Array Linear Array
Linear Array ScanningTwo techniques for activating groups of linear
transducersSwitched Arrays
activate all elements in group at same timePhased Arrays
Activate group elements at slightly different timesimpose timing delays between activations of elements in group
Linear Switched ArraysbullElements energized as groups
ndashgroup acts like one large transducer
bullGroups moved up amp down through elements
ndashsame effect as manually translating
ndashvery fast scanning possible (several times per second)
bullresults in real time image
Linear Switched Arrays
Linear Phased ArraybullGroups of elements energizedndashsame as with switched arraysbullvoltage pulse applied to all
elements of a groupBUT
bullelements not all pulsed at same time
1
2
Linear Phased Arraybulltiming variations allow beam to
be ndashshapedndashsteeredndashfocused
Above arrows indicate timing variations
By activating bottom element first amp top last beam directed upward
Beam steered upward
Linear Phased Array
Above arrows indicate timing variationsBy activating top
element first amp bottom last beam directed
downward
Beam steered downward
By changing timing variations between pulses beam can be scanned from top to bottom
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Krautkramer NDT Ultrasonic Systems
An alternating voltage generates crystal oscillations at the frequency f
U(f)
Sound wave with
frequency f
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
A short voltage pulse generates an oscillation at the crystallsquos resonantfrequency f0 OPERATING FREQUNCY
Short pulse lt ( 1 micros)
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
How to receive sound waves
A sound wave hitting a piezoelectric crystal induces crystal vibration which then causes electrical voltages at the crystal surfaces
Electrical energy
Piezoelectrical crystal Ultrasonic wave
Krautkramer NDT Ultrasonic Systems
N
Near field Far field
Focus Angle of divergenceCrystalAccoustical axis
D0
6
Sound field
Transducer array
bull Transducer = ARRAY OF PIEZOELECTRICAL ELEMENTS Typically 128 to 512
bull SPECFICATIONndash Materialndash ARRAY LENGHTndash Frequency rang
bull resolutionndash Depth CMndash Type
bull LINEAR ARRAYbull PHASED ARRAY
Ultrasound Display
bull One sound pulse producesndash one image scan line
bull one series of gray shade dots in a line
bull Multiple pulsesndash two dimensional image
obtained by moving direction in which sound transmitted
Real-time Scanning
Each pulse generates one lineExcept for multiple focal zones
one frame consists of many individual scan lines
lines framesPRF (Hz) = ------------ X--------------
frame sec
One pulse = one line
Linear Curved linear array Phased arraysectorEndocavitary Intraoperative
Transducer ArraysbullVirtually all commercial transducers are
arraysndashMultiple small elements in single housing
bullAllows sound beam to be electronicallyndashFocusedndashSteeredndashShaped
Electronic Scanning
bullTransducer ArraysndashMultiple small transducersndashActivated in groups
Electrical ScanningPerformed with transducer arrays
multiple elements inside transducer assembly arranged in either
a line (linear array)
concentric circles (annular array)
Curvilinear Array Linear Array
Linear Array ScanningTwo techniques for activating groups of linear
transducersSwitched Arrays
activate all elements in group at same timePhased Arrays
Activate group elements at slightly different timesimpose timing delays between activations of elements in group
Linear Switched ArraysbullElements energized as groups
ndashgroup acts like one large transducer
bullGroups moved up amp down through elements
ndashsame effect as manually translating
ndashvery fast scanning possible (several times per second)
bullresults in real time image
Linear Switched Arrays
Linear Phased ArraybullGroups of elements energizedndashsame as with switched arraysbullvoltage pulse applied to all
elements of a groupBUT
bullelements not all pulsed at same time
1
2
Linear Phased Arraybulltiming variations allow beam to
be ndashshapedndashsteeredndashfocused
Above arrows indicate timing variations
By activating bottom element first amp top last beam directed upward
Beam steered upward
Linear Phased Array
Above arrows indicate timing variationsBy activating top
element first amp bottom last beam directed
downward
Beam steered downward
By changing timing variations between pulses beam can be scanned from top to bottom
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Krautkramer NDT Ultrasonic Systems
A short voltage pulse generates an oscillation at the crystallsquos resonantfrequency f0 OPERATING FREQUNCY
Short pulse lt ( 1 micros)
Piezoelectric Effect
Krautkramer NDT Ultrasonic Systems
How to receive sound waves
A sound wave hitting a piezoelectric crystal induces crystal vibration which then causes electrical voltages at the crystal surfaces
Electrical energy
Piezoelectrical crystal Ultrasonic wave
Krautkramer NDT Ultrasonic Systems
N
Near field Far field
Focus Angle of divergenceCrystalAccoustical axis
D0
6
Sound field
Transducer array
bull Transducer = ARRAY OF PIEZOELECTRICAL ELEMENTS Typically 128 to 512
bull SPECFICATIONndash Materialndash ARRAY LENGHTndash Frequency rang
bull resolutionndash Depth CMndash Type
bull LINEAR ARRAYbull PHASED ARRAY
Ultrasound Display
bull One sound pulse producesndash one image scan line
bull one series of gray shade dots in a line
bull Multiple pulsesndash two dimensional image
obtained by moving direction in which sound transmitted
Real-time Scanning
Each pulse generates one lineExcept for multiple focal zones
one frame consists of many individual scan lines
lines framesPRF (Hz) = ------------ X--------------
frame sec
One pulse = one line
Linear Curved linear array Phased arraysectorEndocavitary Intraoperative
Transducer ArraysbullVirtually all commercial transducers are
arraysndashMultiple small elements in single housing
bullAllows sound beam to be electronicallyndashFocusedndashSteeredndashShaped
Electronic Scanning
bullTransducer ArraysndashMultiple small transducersndashActivated in groups
Electrical ScanningPerformed with transducer arrays
multiple elements inside transducer assembly arranged in either
a line (linear array)
concentric circles (annular array)
Curvilinear Array Linear Array
Linear Array ScanningTwo techniques for activating groups of linear
transducersSwitched Arrays
activate all elements in group at same timePhased Arrays
Activate group elements at slightly different timesimpose timing delays between activations of elements in group
Linear Switched ArraysbullElements energized as groups
ndashgroup acts like one large transducer
bullGroups moved up amp down through elements
ndashsame effect as manually translating
ndashvery fast scanning possible (several times per second)
bullresults in real time image
Linear Switched Arrays
Linear Phased ArraybullGroups of elements energizedndashsame as with switched arraysbullvoltage pulse applied to all
elements of a groupBUT
bullelements not all pulsed at same time
1
2
Linear Phased Arraybulltiming variations allow beam to
be ndashshapedndashsteeredndashfocused
Above arrows indicate timing variations
By activating bottom element first amp top last beam directed upward
Beam steered upward
Linear Phased Array
Above arrows indicate timing variationsBy activating top
element first amp bottom last beam directed
downward
Beam steered downward
By changing timing variations between pulses beam can be scanned from top to bottom
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Krautkramer NDT Ultrasonic Systems
How to receive sound waves
A sound wave hitting a piezoelectric crystal induces crystal vibration which then causes electrical voltages at the crystal surfaces
Electrical energy
Piezoelectrical crystal Ultrasonic wave
Krautkramer NDT Ultrasonic Systems
N
Near field Far field
Focus Angle of divergenceCrystalAccoustical axis
D0
6
Sound field
Transducer array
bull Transducer = ARRAY OF PIEZOELECTRICAL ELEMENTS Typically 128 to 512
bull SPECFICATIONndash Materialndash ARRAY LENGHTndash Frequency rang
bull resolutionndash Depth CMndash Type
bull LINEAR ARRAYbull PHASED ARRAY
Ultrasound Display
bull One sound pulse producesndash one image scan line
bull one series of gray shade dots in a line
bull Multiple pulsesndash two dimensional image
obtained by moving direction in which sound transmitted
Real-time Scanning
Each pulse generates one lineExcept for multiple focal zones
one frame consists of many individual scan lines
lines framesPRF (Hz) = ------------ X--------------
frame sec
One pulse = one line
Linear Curved linear array Phased arraysectorEndocavitary Intraoperative
Transducer ArraysbullVirtually all commercial transducers are
arraysndashMultiple small elements in single housing
bullAllows sound beam to be electronicallyndashFocusedndashSteeredndashShaped
Electronic Scanning
bullTransducer ArraysndashMultiple small transducersndashActivated in groups
Electrical ScanningPerformed with transducer arrays
multiple elements inside transducer assembly arranged in either
a line (linear array)
concentric circles (annular array)
Curvilinear Array Linear Array
Linear Array ScanningTwo techniques for activating groups of linear
transducersSwitched Arrays
activate all elements in group at same timePhased Arrays
Activate group elements at slightly different timesimpose timing delays between activations of elements in group
Linear Switched ArraysbullElements energized as groups
ndashgroup acts like one large transducer
bullGroups moved up amp down through elements
ndashsame effect as manually translating
ndashvery fast scanning possible (several times per second)
bullresults in real time image
Linear Switched Arrays
Linear Phased ArraybullGroups of elements energizedndashsame as with switched arraysbullvoltage pulse applied to all
elements of a groupBUT
bullelements not all pulsed at same time
1
2
Linear Phased Arraybulltiming variations allow beam to
be ndashshapedndashsteeredndashfocused
Above arrows indicate timing variations
By activating bottom element first amp top last beam directed upward
Beam steered upward
Linear Phased Array
Above arrows indicate timing variationsBy activating top
element first amp bottom last beam directed
downward
Beam steered downward
By changing timing variations between pulses beam can be scanned from top to bottom
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Krautkramer NDT Ultrasonic Systems
N
Near field Far field
Focus Angle of divergenceCrystalAccoustical axis
D0
6
Sound field
Transducer array
bull Transducer = ARRAY OF PIEZOELECTRICAL ELEMENTS Typically 128 to 512
bull SPECFICATIONndash Materialndash ARRAY LENGHTndash Frequency rang
bull resolutionndash Depth CMndash Type
bull LINEAR ARRAYbull PHASED ARRAY
Ultrasound Display
bull One sound pulse producesndash one image scan line
bull one series of gray shade dots in a line
bull Multiple pulsesndash two dimensional image
obtained by moving direction in which sound transmitted
Real-time Scanning
Each pulse generates one lineExcept for multiple focal zones
one frame consists of many individual scan lines
lines framesPRF (Hz) = ------------ X--------------
frame sec
One pulse = one line
Linear Curved linear array Phased arraysectorEndocavitary Intraoperative
Transducer ArraysbullVirtually all commercial transducers are
arraysndashMultiple small elements in single housing
bullAllows sound beam to be electronicallyndashFocusedndashSteeredndashShaped
Electronic Scanning
bullTransducer ArraysndashMultiple small transducersndashActivated in groups
Electrical ScanningPerformed with transducer arrays
multiple elements inside transducer assembly arranged in either
a line (linear array)
concentric circles (annular array)
Curvilinear Array Linear Array
Linear Array ScanningTwo techniques for activating groups of linear
transducersSwitched Arrays
activate all elements in group at same timePhased Arrays
Activate group elements at slightly different timesimpose timing delays between activations of elements in group
Linear Switched ArraysbullElements energized as groups
ndashgroup acts like one large transducer
bullGroups moved up amp down through elements
ndashsame effect as manually translating
ndashvery fast scanning possible (several times per second)
bullresults in real time image
Linear Switched Arrays
Linear Phased ArraybullGroups of elements energizedndashsame as with switched arraysbullvoltage pulse applied to all
elements of a groupBUT
bullelements not all pulsed at same time
1
2
Linear Phased Arraybulltiming variations allow beam to
be ndashshapedndashsteeredndashfocused
Above arrows indicate timing variations
By activating bottom element first amp top last beam directed upward
Beam steered upward
Linear Phased Array
Above arrows indicate timing variationsBy activating top
element first amp bottom last beam directed
downward
Beam steered downward
By changing timing variations between pulses beam can be scanned from top to bottom
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Transducer array
bull Transducer = ARRAY OF PIEZOELECTRICAL ELEMENTS Typically 128 to 512
bull SPECFICATIONndash Materialndash ARRAY LENGHTndash Frequency rang
bull resolutionndash Depth CMndash Type
bull LINEAR ARRAYbull PHASED ARRAY
Ultrasound Display
bull One sound pulse producesndash one image scan line
bull one series of gray shade dots in a line
bull Multiple pulsesndash two dimensional image
obtained by moving direction in which sound transmitted
Real-time Scanning
Each pulse generates one lineExcept for multiple focal zones
one frame consists of many individual scan lines
lines framesPRF (Hz) = ------------ X--------------
frame sec
One pulse = one line
Linear Curved linear array Phased arraysectorEndocavitary Intraoperative
Transducer ArraysbullVirtually all commercial transducers are
arraysndashMultiple small elements in single housing
bullAllows sound beam to be electronicallyndashFocusedndashSteeredndashShaped
Electronic Scanning
bullTransducer ArraysndashMultiple small transducersndashActivated in groups
Electrical ScanningPerformed with transducer arrays
multiple elements inside transducer assembly arranged in either
a line (linear array)
concentric circles (annular array)
Curvilinear Array Linear Array
Linear Array ScanningTwo techniques for activating groups of linear
transducersSwitched Arrays
activate all elements in group at same timePhased Arrays
Activate group elements at slightly different timesimpose timing delays between activations of elements in group
Linear Switched ArraysbullElements energized as groups
ndashgroup acts like one large transducer
bullGroups moved up amp down through elements
ndashsame effect as manually translating
ndashvery fast scanning possible (several times per second)
bullresults in real time image
Linear Switched Arrays
Linear Phased ArraybullGroups of elements energizedndashsame as with switched arraysbullvoltage pulse applied to all
elements of a groupBUT
bullelements not all pulsed at same time
1
2
Linear Phased Arraybulltiming variations allow beam to
be ndashshapedndashsteeredndashfocused
Above arrows indicate timing variations
By activating bottom element first amp top last beam directed upward
Beam steered upward
Linear Phased Array
Above arrows indicate timing variationsBy activating top
element first amp bottom last beam directed
downward
Beam steered downward
By changing timing variations between pulses beam can be scanned from top to bottom
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Ultrasound Display
bull One sound pulse producesndash one image scan line
bull one series of gray shade dots in a line
bull Multiple pulsesndash two dimensional image
obtained by moving direction in which sound transmitted
Real-time Scanning
Each pulse generates one lineExcept for multiple focal zones
one frame consists of many individual scan lines
lines framesPRF (Hz) = ------------ X--------------
frame sec
One pulse = one line
Linear Curved linear array Phased arraysectorEndocavitary Intraoperative
Transducer ArraysbullVirtually all commercial transducers are
arraysndashMultiple small elements in single housing
bullAllows sound beam to be electronicallyndashFocusedndashSteeredndashShaped
Electronic Scanning
bullTransducer ArraysndashMultiple small transducersndashActivated in groups
Electrical ScanningPerformed with transducer arrays
multiple elements inside transducer assembly arranged in either
a line (linear array)
concentric circles (annular array)
Curvilinear Array Linear Array
Linear Array ScanningTwo techniques for activating groups of linear
transducersSwitched Arrays
activate all elements in group at same timePhased Arrays
Activate group elements at slightly different timesimpose timing delays between activations of elements in group
Linear Switched ArraysbullElements energized as groups
ndashgroup acts like one large transducer
bullGroups moved up amp down through elements
ndashsame effect as manually translating
ndashvery fast scanning possible (several times per second)
bullresults in real time image
Linear Switched Arrays
Linear Phased ArraybullGroups of elements energizedndashsame as with switched arraysbullvoltage pulse applied to all
elements of a groupBUT
bullelements not all pulsed at same time
1
2
Linear Phased Arraybulltiming variations allow beam to
be ndashshapedndashsteeredndashfocused
Above arrows indicate timing variations
By activating bottom element first amp top last beam directed upward
Beam steered upward
Linear Phased Array
Above arrows indicate timing variationsBy activating top
element first amp bottom last beam directed
downward
Beam steered downward
By changing timing variations between pulses beam can be scanned from top to bottom
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Real-time Scanning
Each pulse generates one lineExcept for multiple focal zones
one frame consists of many individual scan lines
lines framesPRF (Hz) = ------------ X--------------
frame sec
One pulse = one line
Linear Curved linear array Phased arraysectorEndocavitary Intraoperative
Transducer ArraysbullVirtually all commercial transducers are
arraysndashMultiple small elements in single housing
bullAllows sound beam to be electronicallyndashFocusedndashSteeredndashShaped
Electronic Scanning
bullTransducer ArraysndashMultiple small transducersndashActivated in groups
Electrical ScanningPerformed with transducer arrays
multiple elements inside transducer assembly arranged in either
a line (linear array)
concentric circles (annular array)
Curvilinear Array Linear Array
Linear Array ScanningTwo techniques for activating groups of linear
transducersSwitched Arrays
activate all elements in group at same timePhased Arrays
Activate group elements at slightly different timesimpose timing delays between activations of elements in group
Linear Switched ArraysbullElements energized as groups
ndashgroup acts like one large transducer
bullGroups moved up amp down through elements
ndashsame effect as manually translating
ndashvery fast scanning possible (several times per second)
bullresults in real time image
Linear Switched Arrays
Linear Phased ArraybullGroups of elements energizedndashsame as with switched arraysbullvoltage pulse applied to all
elements of a groupBUT
bullelements not all pulsed at same time
1
2
Linear Phased Arraybulltiming variations allow beam to
be ndashshapedndashsteeredndashfocused
Above arrows indicate timing variations
By activating bottom element first amp top last beam directed upward
Beam steered upward
Linear Phased Array
Above arrows indicate timing variationsBy activating top
element first amp bottom last beam directed
downward
Beam steered downward
By changing timing variations between pulses beam can be scanned from top to bottom
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Linear Curved linear array Phased arraysectorEndocavitary Intraoperative
Transducer ArraysbullVirtually all commercial transducers are
arraysndashMultiple small elements in single housing
bullAllows sound beam to be electronicallyndashFocusedndashSteeredndashShaped
Electronic Scanning
bullTransducer ArraysndashMultiple small transducersndashActivated in groups
Electrical ScanningPerformed with transducer arrays
multiple elements inside transducer assembly arranged in either
a line (linear array)
concentric circles (annular array)
Curvilinear Array Linear Array
Linear Array ScanningTwo techniques for activating groups of linear
transducersSwitched Arrays
activate all elements in group at same timePhased Arrays
Activate group elements at slightly different timesimpose timing delays between activations of elements in group
Linear Switched ArraysbullElements energized as groups
ndashgroup acts like one large transducer
bullGroups moved up amp down through elements
ndashsame effect as manually translating
ndashvery fast scanning possible (several times per second)
bullresults in real time image
Linear Switched Arrays
Linear Phased ArraybullGroups of elements energizedndashsame as with switched arraysbullvoltage pulse applied to all
elements of a groupBUT
bullelements not all pulsed at same time
1
2
Linear Phased Arraybulltiming variations allow beam to
be ndashshapedndashsteeredndashfocused
Above arrows indicate timing variations
By activating bottom element first amp top last beam directed upward
Beam steered upward
Linear Phased Array
Above arrows indicate timing variationsBy activating top
element first amp bottom last beam directed
downward
Beam steered downward
By changing timing variations between pulses beam can be scanned from top to bottom
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Transducer ArraysbullVirtually all commercial transducers are
arraysndashMultiple small elements in single housing
bullAllows sound beam to be electronicallyndashFocusedndashSteeredndashShaped
Electronic Scanning
bullTransducer ArraysndashMultiple small transducersndashActivated in groups
Electrical ScanningPerformed with transducer arrays
multiple elements inside transducer assembly arranged in either
a line (linear array)
concentric circles (annular array)
Curvilinear Array Linear Array
Linear Array ScanningTwo techniques for activating groups of linear
transducersSwitched Arrays
activate all elements in group at same timePhased Arrays
Activate group elements at slightly different timesimpose timing delays between activations of elements in group
Linear Switched ArraysbullElements energized as groups
ndashgroup acts like one large transducer
bullGroups moved up amp down through elements
ndashsame effect as manually translating
ndashvery fast scanning possible (several times per second)
bullresults in real time image
Linear Switched Arrays
Linear Phased ArraybullGroups of elements energizedndashsame as with switched arraysbullvoltage pulse applied to all
elements of a groupBUT
bullelements not all pulsed at same time
1
2
Linear Phased Arraybulltiming variations allow beam to
be ndashshapedndashsteeredndashfocused
Above arrows indicate timing variations
By activating bottom element first amp top last beam directed upward
Beam steered upward
Linear Phased Array
Above arrows indicate timing variationsBy activating top
element first amp bottom last beam directed
downward
Beam steered downward
By changing timing variations between pulses beam can be scanned from top to bottom
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Electronic Scanning
bullTransducer ArraysndashMultiple small transducersndashActivated in groups
Electrical ScanningPerformed with transducer arrays
multiple elements inside transducer assembly arranged in either
a line (linear array)
concentric circles (annular array)
Curvilinear Array Linear Array
Linear Array ScanningTwo techniques for activating groups of linear
transducersSwitched Arrays
activate all elements in group at same timePhased Arrays
Activate group elements at slightly different timesimpose timing delays between activations of elements in group
Linear Switched ArraysbullElements energized as groups
ndashgroup acts like one large transducer
bullGroups moved up amp down through elements
ndashsame effect as manually translating
ndashvery fast scanning possible (several times per second)
bullresults in real time image
Linear Switched Arrays
Linear Phased ArraybullGroups of elements energizedndashsame as with switched arraysbullvoltage pulse applied to all
elements of a groupBUT
bullelements not all pulsed at same time
1
2
Linear Phased Arraybulltiming variations allow beam to
be ndashshapedndashsteeredndashfocused
Above arrows indicate timing variations
By activating bottom element first amp top last beam directed upward
Beam steered upward
Linear Phased Array
Above arrows indicate timing variationsBy activating top
element first amp bottom last beam directed
downward
Beam steered downward
By changing timing variations between pulses beam can be scanned from top to bottom
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Electrical ScanningPerformed with transducer arrays
multiple elements inside transducer assembly arranged in either
a line (linear array)
concentric circles (annular array)
Curvilinear Array Linear Array
Linear Array ScanningTwo techniques for activating groups of linear
transducersSwitched Arrays
activate all elements in group at same timePhased Arrays
Activate group elements at slightly different timesimpose timing delays between activations of elements in group
Linear Switched ArraysbullElements energized as groups
ndashgroup acts like one large transducer
bullGroups moved up amp down through elements
ndashsame effect as manually translating
ndashvery fast scanning possible (several times per second)
bullresults in real time image
Linear Switched Arrays
Linear Phased ArraybullGroups of elements energizedndashsame as with switched arraysbullvoltage pulse applied to all
elements of a groupBUT
bullelements not all pulsed at same time
1
2
Linear Phased Arraybulltiming variations allow beam to
be ndashshapedndashsteeredndashfocused
Above arrows indicate timing variations
By activating bottom element first amp top last beam directed upward
Beam steered upward
Linear Phased Array
Above arrows indicate timing variationsBy activating top
element first amp bottom last beam directed
downward
Beam steered downward
By changing timing variations between pulses beam can be scanned from top to bottom
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Linear Array ScanningTwo techniques for activating groups of linear
transducersSwitched Arrays
activate all elements in group at same timePhased Arrays
Activate group elements at slightly different timesimpose timing delays between activations of elements in group
Linear Switched ArraysbullElements energized as groups
ndashgroup acts like one large transducer
bullGroups moved up amp down through elements
ndashsame effect as manually translating
ndashvery fast scanning possible (several times per second)
bullresults in real time image
Linear Switched Arrays
Linear Phased ArraybullGroups of elements energizedndashsame as with switched arraysbullvoltage pulse applied to all
elements of a groupBUT
bullelements not all pulsed at same time
1
2
Linear Phased Arraybulltiming variations allow beam to
be ndashshapedndashsteeredndashfocused
Above arrows indicate timing variations
By activating bottom element first amp top last beam directed upward
Beam steered upward
Linear Phased Array
Above arrows indicate timing variationsBy activating top
element first amp bottom last beam directed
downward
Beam steered downward
By changing timing variations between pulses beam can be scanned from top to bottom
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Linear Switched ArraysbullElements energized as groups
ndashgroup acts like one large transducer
bullGroups moved up amp down through elements
ndashsame effect as manually translating
ndashvery fast scanning possible (several times per second)
bullresults in real time image
Linear Switched Arrays
Linear Phased ArraybullGroups of elements energizedndashsame as with switched arraysbullvoltage pulse applied to all
elements of a groupBUT
bullelements not all pulsed at same time
1
2
Linear Phased Arraybulltiming variations allow beam to
be ndashshapedndashsteeredndashfocused
Above arrows indicate timing variations
By activating bottom element first amp top last beam directed upward
Beam steered upward
Linear Phased Array
Above arrows indicate timing variationsBy activating top
element first amp bottom last beam directed
downward
Beam steered downward
By changing timing variations between pulses beam can be scanned from top to bottom
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Linear Switched Arrays
Linear Phased ArraybullGroups of elements energizedndashsame as with switched arraysbullvoltage pulse applied to all
elements of a groupBUT
bullelements not all pulsed at same time
1
2
Linear Phased Arraybulltiming variations allow beam to
be ndashshapedndashsteeredndashfocused
Above arrows indicate timing variations
By activating bottom element first amp top last beam directed upward
Beam steered upward
Linear Phased Array
Above arrows indicate timing variationsBy activating top
element first amp bottom last beam directed
downward
Beam steered downward
By changing timing variations between pulses beam can be scanned from top to bottom
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Linear Phased ArraybullGroups of elements energizedndashsame as with switched arraysbullvoltage pulse applied to all
elements of a groupBUT
bullelements not all pulsed at same time
1
2
Linear Phased Arraybulltiming variations allow beam to
be ndashshapedndashsteeredndashfocused
Above arrows indicate timing variations
By activating bottom element first amp top last beam directed upward
Beam steered upward
Linear Phased Array
Above arrows indicate timing variationsBy activating top
element first amp bottom last beam directed
downward
Beam steered downward
By changing timing variations between pulses beam can be scanned from top to bottom
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Linear Phased Arraybulltiming variations allow beam to
be ndashshapedndashsteeredndashfocused
Above arrows indicate timing variations
By activating bottom element first amp top last beam directed upward
Beam steered upward
Linear Phased Array
Above arrows indicate timing variationsBy activating top
element first amp bottom last beam directed
downward
Beam steered downward
By changing timing variations between pulses beam can be scanned from top to bottom
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Linear Phased Array
Above arrows indicate timing variationsBy activating top
element first amp bottom last beam directed
downward
Beam steered downward
By changing timing variations between pulses beam can be scanned from top to bottom
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Linear Phased Array
Above arrows indicate timing variations
By activating top amp bottom elements earlier than center ones beam
is focused
Beam is focused
Focus
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Linear Phased ArrayFocus
Focal point can be moved toward or away from transducer by altering timing variations
between outer elements amp center
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Linear Phased ArrayFocus
Multiple focal zones accomplished by changing timing variations between pulsesbullMultiple pulses requiredbullslows frame rate
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Listening ModebullListening direction can be steered amp
focused similarly to beam generation
ndashappropriate timing variations applied to echoes received by various
elements of a groupbullDynamic Focusing
ndashlistening focus depth can be changed electronically between pulses by
applying timing variations as above
2
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
15 Transducerbull~3 elements in elevation directionbullAll 3 elements can be combined for thick slicebull1 element can be selected for thin slice
Elevation
Direction
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
15 amp 2D TransducersbullMultiple elements in 2 directionsbullCan be steered amp focused anywhere in 3D
volume
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Remember me to explain why we use the backing block and matching layer
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
What we will use the returned or received ultrasound waves ldquoechoesrdquo
bull NO ECHOES = NO IMAGING bull WE WILL BACK TO THAT
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Perpendicular Incidence
bull Sound beam travels perpendicular to boundary between two media
90o
IncidentAngle
1
2Boundarybetween
media
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Oblique Incidence
bull Sound beam travel not perpendicular to boundary Oblique
IncidentAngle
(not equal to 90o)
1
2
Boundarybetween
media
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Perpendicular Incidence
bull What happens to sound at boundaryndash reflected
bull sound returns toward source
ndash transmittedbull sound continues in
same direction
1
2
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Perpendicular Incidence
bull Fraction of intensity reflected depends on acoustic impedances of two media 1
2
Acoustic Impedance= Density X Speed of Sound
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Intensity Reflection Coefficient (IRC)amp
Intensity Transmission Coefficient (ITC)IRC
Fraction of sound intensity reflected at interface
lt1ITC
Fraction of sound intensity transmitted through interface
lt1
Medium 1
Medium 2IRC + ITC = 1
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
IRC Equation
bull Z1 is acoustic impedance of medium 1
bull Z2 is acoustic impedance of medium 2
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
For perpendicular incidence
Medium 1
Medium 2
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Reflections
Impedances equal no reflection
Impedances similarlittle reflected
Impedances very different (boneair interference)virtually all reflected
2 reflected intensity z2 - z1
Fraction Reflected---------- = ------------------------ = incident intensity z2 + z1
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Why Use Gel and matching layer
Acoustic Impedance of air amp soft tissue very differentWithout gel virtually no sound penetrates skin
2 reflected intensity z2 - z1
IRC---------- = ------------------------ = incident intensity z2 + z1
Acoustic Impedance
(rayls)
Air 400Soft Tissue 1630000
Fraction Reflected 09995
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
THE BASICS US IDEA
bull The returned echoes represent gray levels in ultrasound images
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
What does your scanner know about echoed sound
What was the time delay between sound broadcast and the echo
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
What Does Your Scanner Assume about Echoes
(or how the scanner can lie to you)
bull Sound travels at 1540 ms everywhere in bodyndash average speed of sound in soft tissue
bull Sound travels in straight lines in direction transmitted
bull Sound attenuated equally by everything in bodyndash (05 dBcmMHz soft tissue average)
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Distance of Echo from Transducer
bull Time delay accurately measured by scanner
distance = time delay X speed of sound
distance
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
What is the Speed of Sound
bull scanner assumes speed of sound is that of soft tissuendash 154 mmmsecndash 1540 msecndash 13 usec required for echo object 1 cm from
transducer (2 cm round trip)
distance = time delay X speed of sound
1 cm13 msec
Handy rule of
thumb
bullB AND M-modebullColor spectral power DopplerbullTissue harmonic imaging (detection of harmonics signals abdominal and liver)bullContrast agent imaging (detection of subtle parenchymal change and metastases in the liver abdominal and vascular)bull3-D imaging
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
So the scanner assumes the wrong speed
bull Sometimes
soft tissue ==gt 154 mm msecfat ==gt 144 mm msecbrain ==gt 151 mm msecliver kidney ==gt 156 mm msecmuscle ==gt 157 mm msec
bullLuckily the speed of sound is almost the same for most body parts
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Attenuation Correction
bull scanner assumes entire body has attenuation of soft tissuendash actual attenuation
varies widely in body
bull Fat 06bull Brain 06bull Liver 05bull Kidney 09bull Muscle 10bull Heart 11
Tissue Attenuation Coefficient( dB cm MHz)
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Gray Shade of Echo
bull Ultrasound is gray shade modality
bull Gray shade should indicate echogeneity of object
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
How does scanner know what gray shade to assign an echo
bull Based upon intensity (volume loudness) of echo
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
How to reconstruct the image from echoes
bull US MODESndash B AND M-modendash Color spectral power Dopplerndash Tissue harmonic imaging (detection of harmonics
signals abdominal and liver)ndash Contrast agent imaging (detection of subtle
parenchymal change and metastases in the liver abdominal and vascular)
ndash 3-D imaging
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
M Modebull Multiple pulses in same
locationndash New lines added to right
bull horizontal axisndash elapsed time (not time within a
pulse)bull vertical axis
ndash time delay between pulse amp echobull indicates distance of reflector from
transducer
Elapsed Time
Each vertical line is one pulse
Echo Delay Time
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
M-Mode (left ventricle)
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Scanner Processing of Echoes
AmplificationCompensationCompressionDemodulationRejection
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Amplification
bull Increases small voltage signals from transducerndash incoming voltage signal
bull 10rsquos of millivolts
bull larger voltage required for processing amp storage
Amplifier
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Compensation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Need for Compensationbull equal intensity reflections from
different depths return with different intensitiesndash different travel distances
bull attenuation is function of path length
Display without compensation
time since pulse
echointensity
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Equal Echoes
VoltageAmplification
VoltageAmplitude
afterAmplification
Equal echoesequal voltages
Later EchoesEarly Echoes
Voltagebefore
Compensation
Time within a pulse
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Compensation (TGC)bull Body attenuation varies from 05 dBcmMHzbull TGC allows manual fine tuning of compensation vs
delay bull TGC curve often displayed graphically
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Compensation (TGC)
bull TGC adjustment affects all echoes at a specific distance range from transducer
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Compression
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Compression1000
1 10 100 1000
3 = log 1000
1 10 100 1000
2= log 100
1 = log 10
0 = log 10
100000100001000100101
543210
Input LogarithmCanrsquot easily distinguish
between 1 amp 10 here
Difference between 1 amp 10 the same as
between 100 amp 1000
Logarithms stretch low end of scale compress high end
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Demodulation
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Demodulationbull Intensity information carried on ldquoenveloperdquo of
operating frequencyrsquos sine wavendash varying amplitude of sine wave
bull demodulation separates intensity information from sine wave
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Demodulation Sub-steps
bull rectifyndash turn negative signals
positivebull smooth
ndash follow peaks
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Rejection
bullAmplificationbullCompensationbullCompressionbullDemodulationbullRejection
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Rejectionbull also known as
ndash suppressionndash threshold
bull objectndash eliminate small amplitude
voltage pulsesbull reason
ndash reduce noisebull electronic noisebull acoustic noise
ndash noise contributes no useful information to image
Amplitudes below dotted line reset to zero
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Image Resolution
bull Detail Resolutionndash spatial resolutionndash separation required to
produce separate reflectionsbull Detail Resolution types
Axial
Lateral
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Resolution amp Reflector Sizeminimum imaged size of a reflector in each dimension
is equal to resolutionObjects never imaged smaller than systemrsquos resolution
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Axial Resolution
minimum reflector separation in direction of sound travel which produces separate reflections
depends on spatial pulse lengthDistance in space covered by a pulse
HEYHEY
Spatial Pulse Length
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Axial Resolution
Separationjust greaterthan half thespatialpulse length
GapSeparate
Echoes
Axial Resolution = Spatial Pulse Length 2
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Axial Resolution
Separationjust lessthan half thespatialpulse length
OverlapNo GapNo SeparateEchoes
Axial Resolution = Spatial Pulse Length 2
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Spatial Pulse LengthSpat Pulse Length = cycles per pulse X wavelength
Wavelength = Speed Frequency
Duty Factor = Pulse Duration X Pulse Repetition Freq
CYCLES
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
WavelengthCalculate SPL for 5 MHz sound in
soft tissue 5 cycles per pulse
(Wavelength=031 mmcycle)
SPL = 031 mm cycle X 5 cycles pulse = 155 mm pulse
Spat Pulse Length = cycles per pulse X wavelength
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Improve Axial Resolution by Reducing Spatial Pulse Length
bull increase frequencyndash Decreases wavelengthndash decreases penetration
limits imaging depthbull Reduce cycles per
pulsendash requires damping
bull reduces intensitybull increases bandwidth
Spat Pulse Length = cycles per pulse X wavelength
Speed = Wavelength X Frequency
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Lateral Resolution
bull Definitionndash minimum separation between reflectors in
direction perpendicular to beam travel which produces separate reflections when the beam is scanned across themLateral Resolution = Beam Diameter
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Lateral Resolution
bull if separation is greater than beam diameter objects can be resolved as two reflectors
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Lateral Resolution
bull Complicationndash beam diameter
varies with distance from transducer
ndash Near zone length varies with
bull Frequencybull transducer
diameter
Near zone lengthNearzone
Farzone
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Contrast Resolution
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Contrast Resolution
bull difference in echo intensity between 2 echoes for them to be assigned different digital values
89
88
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Pre-Processing
bull Assigning of specific values to analog echo intensities
bull analog to digital (AD) converterbull converts output signal from receiver
(after rejection) to a value
89
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Gray Scalebull the more candidate values for a pixel
ndash the more shades of gray image can be stored in digital image
ndash The less difference between echo intensity required to guarantee different pixel values
bull See next slide
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
1234567
1 2 6 6 4 4 5 3 2 3 7 7 6 4 2 5 5 2
1234567
2 4 11 11 7 8 10 6 3 6 14 14 11 6 4 8 12 4
89
1011121314
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Display Limitationsbull not possible to display all shades of gray
simultaneouslybull window amp level controls determine how pixel
values are mapped to gray shades bull numbers (pixel values) do not change window amp
level only change gray shade mapping
17 =
65 =
Change window
level
17 =
65 =
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Presentation of Brightness Levelsbull pixel values assigned brightness levels
ndash pre-processingbull manipulating brightness levels does not affect
image datandash post-processing
bull windowbull level
125 25 311 111 182 222 176
199 192 85 69 133 149 112
77 103 118 139 154 125 120
145 301 256 223 287 256 225
178 322 325 299 353 333 300
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Block Diagram
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
B Mode
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Color flow imaging (mode)Color Doppler (mode)
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Continuous wave (CW) Doppler
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
M-mode
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Power Doppler (mode)
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Pulsed wave Doppler
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Transducerfrequency MHZ
Depth cm Mode Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Transducerfrequency MHZ
Depth cm Mode
Min Req
Abdominal liver spleen kidney gallbladder pancreas and retroperitoneum
LCAPA2-7 min2-10 req
15 18 B
LCAPA2-515-4
10 15 Spectral Doppler
LCAPA2-5 min15-4 req
10 15 Flow imaging
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Small parts LA7-10 min5-15 req
6 8-10 Dynamic imaging
LA4-5 min4-8 req
6 8-10 Spectral Doppler
LA4-5 min4-8 req
6 8-10 Flow imaging
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Vascular LACLA2-8 MIN2-10 REQ
6 8 Dynamic imaging
LACLA2-8 MIN2-10 REQ
6 8 Spectral Doppler
LACLA3-5 MIN3-6 REQ
6 10Flow imaging
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
DOPPLER US
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Hemodynamics
bull Plugbull Laminarbull Disturbedbull Turbulent
Blood Flow Characterization
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Plug Flow
bull Type of normal flowbull Constant fluid speed across
tubebull Occurs near entrance of flow
into tube
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Laminar Flow
also called parabolic flowfluid layers slide over one anotheroccurs further from entrance to tubecentral portion of fluid moves at
maximum speedflow near vessel wall hardly moves
at allfriction with wall
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
FlowDisturbed Flow
Normal parallel stream lines disturbedprimarily forward particles still flow
Turbulent Flowrandom amp chaoticindividual particles flow in all directionsnet flow is forwardOften occurs beyond obstruction
such as plaque on vessel wall
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Flow Pressure amp Resistancebull Pressure
ndash pressure difference between ends of tube drives fluid flow
bull Resistancendash more resistance = lower flow ratendash resistance affected by
bull fluidrsquos viscositybull vessel lengthbull vessel diameter
ndash flow for a given pressure determined by resistance
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Doppler Shift
bull difference between received amp transmitted frequency
bull caused by relative motion between sound source amp receiver
bull Frequency shift indicative of reflector speed
IN OUT
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Doppler Examplesbull change in pitch of as object approaches amp
leaves observerndash trainndash Ambulance siren
bull moving blood cellsndash motion can be presented as sound or as an image
Doppler Angle
bull angle between sound travel amp flow
bull 0 degreesndash flow in direction of sound travel
bull 90 degreesndash flow perpendicular to sound travel
q
Flow Components
ndash Flow vector can be separated into two vectors
Flow parallel to sound
Flow perpendicular to sound
Doppler SensingOnly flow parallel to sound
sensed by scanner
Flow parallel to
sound
Flow perpendicular to sound
Doppler Sensing
Sensed flow always lt actual flow
Sensed flow
Actual flow
Doppler Sensing
ndash cos(q) = SF AF
Sensed flow
(SF)
Actual flow
(AF)q
q
Doppler Equation
bull wherefD =Doppler Shift in MHzfe = echo of reflected frequency (MHz)fo = operating frequency (MHz)v = reflector speed (ms)q = angle between flow amp sound propagationc = speed of sound in soft tissue (ms)
2 X fo X v X cosqf D = fe - fo------------------------- =
cq
Relationships
bull positive shift when reflector moving toward transducerndash echoed frequency gt operating frequency
bull negative shift when reflector moving away from transducerndash echoed frequency lt operating frequency
2 X fo X v X cosqf D = fe - fo------------------------- =
c
q
q
Relationships
bull Doppler angle affects measured Doppler shift
2 X fo X v X cosqf D = fe - fo------------------------- =
c
q
q
cosq
Doppler Relationships
bull higher reflector speed results in greater Doppler shift
bull higher operating frequency results in greater Doppler shift
bull larger Doppler angle results in lower Doppler shift
q 77 X fD (kHz)
v (cms)-------------------------- = fo (MHz) X cosq
Continuous Wave Doppler
bull Audio presentation onlybull No imagebull Useful as fetal dose monitor
Continuous Wave Doppler
bull 2 transducers usedndash one continuously transmits
bull voltage frequency = transducerrsquos operating frequency
ndash typically 2-10 MHz
ndash one continuously receivesbull Reception Area
ndash flow detected within overlap of transmit amp receive sound beams
Continuous Wave DopplerReceiver Function
bull receives reflected sound wavesbull Subtract signals
ndash detects frequency shiftndash typical shift ~ 11000 th of source frequency
bull usually in audible sound range
bull Amplify subtracted signalbull Play directly on speaker
- =
Pulse Wave vs Continuous Wave Doppler
Continuous Wave Pulse Wave
No Image Image
Sound on continuously
Both imaging amp Doppler sound pulses generated
Dangers of Ultrasound
bullThere have been many concerns about the safety of ultrasound
ndashBecause ultrasound is energy the question becomes What is this energy doing to my tissues
or my baby
bullThere have been some reports of low birthweight babies being born to mothers who
had frequent ultrasound examinations during pregnancy
bullThe two major possibilities with ultrasound are as follows
ndashdevelopment of heat - tissues or water absorb the ultrasound energy which increases their
temperature locally ndashformation of bubbles (cavitation) - when dissolved
gases come out of solution due to local heat caused by ultrasound
bullHowever there have been no substantiated ill-effects of ultrasound documented in studies in
either humans or animals ndashThis being said ultrasound should still be used
only when necessary (ie better to be cautious)
Ultrasound Terminology
bull Impedance resistancebull steered
PZT is Most Common Piezoelectric Material
bullLead Zirconate TitanatebullAdvantages
ndashEfficientbullMore electrical energy transferred to sound amp vice-versa
ndashHigh natural resonance frequencyndashRepeatable characteristics
bullStable designbullDisadvantages
ndashHigh acoustic impedancebullCan cause poor acoustic couplingbullRequires matching layer to compensate
- UltarSound Machine Dr Fadhl Alakwaa
- What are the first things to account when purchasing new US equ
- EXCELLENT RESOURCES
- CLINICAL APPLICATIONS
- Slide 5
- Slide 6
- Slide 7
- What do you need to know to be professional in US
- Advantage of US OVER other modalities
- US development
- Slide 11
- What is Ultrasound machine
- Spectrum of sound
- Sound propagation
- Slide 15
- Wave propagation
- Difference between EM and sound
- How to produce sound wave
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Sound field
- Slide 26
- Transducer array
- Slide 28
- Ultrasound Display
- Real-time Scanning
- Linear Curved linear array Phased arraysector Endocavitary
- Transducer Arrays
- Electronic Scanning
- Electrical Scanning
- Linear Array Scanning
- Linear Switched Arrays
- Linear Switched Arrays (2)
- Linear Phased Array
- Linear Phased Array (2)
- Linear Phased Array (3)
- Linear Phased Array (4)
- Linear Phased Array (5)
- Linear Phased Array (6)
- Listening Mode
- 15 Transducer
- 15 amp 2D Transducers
- Remember me to explain why we use the backing block and matchin
- What we will use the returned or received ultrasound waves ldquoech
- Perpendicular Incidence
- Oblique Incidence
- Perpendicular Incidence (2)
- Perpendicular Incidence (3)
- Intensity Reflection Coefficient (IRC) amp Intensity Transmission
- IRC Equation
- Reflections
- Why Use Gel and matching layer
- Slide 57
- THE BASICS US IDEA
- What does your scanner know about echoed sound
- What Does Your Scanner Assume about Echoes (or how the scanner
- Distance of Echo from Transducer
- What is the Speed of Sound
- So the scanner assumes the wrong speed
- Attenuation Correction
- Gray Shade of Echo
- How does scanner know what gray shade to assign an echo
- How to reconstruct the image from echoes
- M Mode
- M-Mode (left ventricle)
- Scanner Processing of Echoes
- Amplification
- Compensation
- Need for Compensation
- Equal Echoes
- Compensation (TGC)
- Compensation (TGC) (2)
- Compression
- Compression (2)
- Demodulation
- Demodulation (2)
- Demodulation Sub-steps
- Rejection
- Rejection (2)
- Image Resolution
- Resolution amp Reflector Size
- Axial Resolution
- Axial Resolution (2)
- Axial Resolution (3)
- Spatial Pulse Length
- Wavelength
- Improve Axial Resolution by Reducing Spatial Pulse Length
- Slide 92
- Lateral Resolution
- Lateral Resolution (2)
- Lateral Resolution (3)
- Contrast Resolution
- Contrast Resolution (2)
- Pre-Processing
- Gray Scale
- Slide 100
- Display Limitations
- Presentation of Brightness Levels
- Slide 103
- Block Diagram
- B Mode
- Color flow imaging (mode) Color Doppler (mode)
- Continuous wave (CW) Doppler
- M-mode
- Power Doppler (mode)
- Pulsed wave Doppler
- Slide 111
- Slide 112
- Slide 113
- Slide 114
- DOPPLER US
- Hemodynamics
- Plug Flow
- Laminar Flow
- Flow
- Flow Pressure amp Resistance
- Doppler Shift
- Doppler Examples
- Doppler Angle
- Flow Components
- Doppler Sensing
- Doppler Sensing (2)
- Doppler Sensing (3)
- Doppler Equation
- Relationships
- Relationships (2)
- Doppler Relationships
- Continuous Wave Doppler
- Continuous Wave Doppler (2)
- Continuous Wave Doppler Receiver Function
- Pulse Wave vs Continuous Wave Doppler
- Dangers of Ultrasound
- Slide 137
- Slide 138
- Slide 139
- Ultrasound Terminology
- PZT is Most Common Piezoelectric Material
-
Flow Components
ndash Flow vector can be separated into two vectors
Flow parallel to sound
Flow perpendicular to sound
Doppler SensingOnly flow parallel to sound
sensed by scanner
Flow parallel to
sound
Flow perpendicular to sound
Doppler Sensing
Sensed flow always lt actual flow
Sensed flow
Actual flow
Doppler Sensing
ndash cos(q) = SF AF
Sensed flow
(SF)
Actual flow
(AF)q
q
Doppler Equation
bull wherefD =Doppler Shift in MHzfe = echo of reflected frequency (MHz)fo = operating frequency (MHz)v = reflector speed (ms)q = angle between flow amp sound propagationc = speed of sound in soft tissue (ms)
2 X fo X v X cosqf D = fe - fo------------------------- =
cq
Relationships
bull positive shift when reflector moving toward transducerndash echoed frequency gt operating frequency
bull negative shift when reflector moving away from transducerndash echoed frequency lt operating frequency
2 X fo X v X cosqf D = fe - fo------------------------- =
c
q
q
Relationships
bull Doppler angle affects measured Doppler shift
2 X fo X v X cosqf D = fe - fo------------------------- =
c
q
q
cosq
Doppler Relationships
bull higher reflector speed results in greater Doppler shift
bull higher operating frequency results in greater Doppler shift
bull larger Doppler angle results in lower Doppler shift
q 77 X fD (kHz)
v (cms)-------------------------- = fo (MHz) X cosq
Continuous Wave Doppler
bull Audio presentation onlybull No imagebull Useful as fetal dose monitor
Continuous Wave Doppler
bull 2 transducers usedndash one continuously transmits
bull voltage frequency = transducerrsquos operating frequency
ndash typically 2-10 MHz
ndash one continuously receivesbull Reception Area
ndash flow detected within overlap of transmit amp receive sound beams
Continuous Wave DopplerReceiver Function
bull receives reflected sound wavesbull Subtract signals
ndash detects frequency shiftndash typical shift ~ 11000 th of source frequency
bull usually in audible sound range
bull Amplify subtracted signalbull Play directly on speaker
- =
Pulse Wave vs Continuous Wave Doppler
Continuous Wave Pulse Wave
No Image Image
Sound on continuously
Both imaging amp Doppler sound pulses generated
Dangers of Ultrasound
bullThere have been many concerns about the safety of ultrasound
ndashBecause ultrasound is energy the question becomes What is this energy doing to my tissues
or my baby
bullThere have been some reports of low birthweight babies being born to mothers who
had frequent ultrasound examinations during pregnancy
bullThe two major possibilities with ultrasound are as follows
ndashdevelopment of heat - tissues or water absorb the ultrasound energy which increases their
temperature locally ndashformation of bubbles (cavitation) - when dissolved
gases come out of solution due to local heat caused by ultrasound
bullHowever there have been no substantiated ill-effects of ultrasound documented in studies in
either humans or animals ndashThis being said ultrasound should still be used
only when necessary (ie better to be cautious)
Ultrasound Terminology
bull Impedance resistancebull steered
PZT is Most Common Piezoelectric Material
bullLead Zirconate TitanatebullAdvantages
ndashEfficientbullMore electrical energy transferred to sound amp vice-versa
ndashHigh natural resonance frequencyndashRepeatable characteristics
bullStable designbullDisadvantages
ndashHigh acoustic impedancebullCan cause poor acoustic couplingbullRequires matching layer to compensate
- UltarSound Machine Dr Fadhl Alakwaa
- What are the first things to account when purchasing new US equ
- EXCELLENT RESOURCES
- CLINICAL APPLICATIONS
- Slide 5
- Slide 6
- Slide 7
- What do you need to know to be professional in US
- Advantage of US OVER other modalities
- US development
- Slide 11
- What is Ultrasound machine
- Spectrum of sound
- Sound propagation
- Slide 15
- Wave propagation
- Difference between EM and sound
- How to produce sound wave
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Sound field
- Slide 26
- Transducer array
- Slide 28
- Ultrasound Display
- Real-time Scanning
- Linear Curved linear array Phased arraysector Endocavitary
- Transducer Arrays
- Electronic Scanning
- Electrical Scanning
- Linear Array Scanning
- Linear Switched Arrays
- Linear Switched Arrays (2)
- Linear Phased Array
- Linear Phased Array (2)
- Linear Phased Array (3)
- Linear Phased Array (4)
- Linear Phased Array (5)
- Linear Phased Array (6)
- Listening Mode
- 15 Transducer
- 15 amp 2D Transducers
- Remember me to explain why we use the backing block and matchin
- What we will use the returned or received ultrasound waves ldquoech
- Perpendicular Incidence
- Oblique Incidence
- Perpendicular Incidence (2)
- Perpendicular Incidence (3)
- Intensity Reflection Coefficient (IRC) amp Intensity Transmission
- IRC Equation
- Reflections
- Why Use Gel and matching layer
- Slide 57
- THE BASICS US IDEA
- What does your scanner know about echoed sound
- What Does Your Scanner Assume about Echoes (or how the scanner
- Distance of Echo from Transducer
- What is the Speed of Sound
- So the scanner assumes the wrong speed
- Attenuation Correction
- Gray Shade of Echo
- How does scanner know what gray shade to assign an echo
- How to reconstruct the image from echoes
- M Mode
- M-Mode (left ventricle)
- Scanner Processing of Echoes
- Amplification
- Compensation
- Need for Compensation
- Equal Echoes
- Compensation (TGC)
- Compensation (TGC) (2)
- Compression
- Compression (2)
- Demodulation
- Demodulation (2)
- Demodulation Sub-steps
- Rejection
- Rejection (2)
- Image Resolution
- Resolution amp Reflector Size
- Axial Resolution
- Axial Resolution (2)
- Axial Resolution (3)
- Spatial Pulse Length
- Wavelength
- Improve Axial Resolution by Reducing Spatial Pulse Length
- Slide 92
- Lateral Resolution
- Lateral Resolution (2)
- Lateral Resolution (3)
- Contrast Resolution
- Contrast Resolution (2)
- Pre-Processing
- Gray Scale
- Slide 100
- Display Limitations
- Presentation of Brightness Levels
- Slide 103
- Block Diagram
- B Mode
- Color flow imaging (mode) Color Doppler (mode)
- Continuous wave (CW) Doppler
- M-mode
- Power Doppler (mode)
- Pulsed wave Doppler
- Slide 111
- Slide 112
- Slide 113
- Slide 114
- DOPPLER US
- Hemodynamics
- Plug Flow
- Laminar Flow
- Flow
- Flow Pressure amp Resistance
- Doppler Shift
- Doppler Examples
- Doppler Angle
- Flow Components
- Doppler Sensing
- Doppler Sensing (2)
- Doppler Sensing (3)
- Doppler Equation
- Relationships
- Relationships (2)
- Doppler Relationships
- Continuous Wave Doppler
- Continuous Wave Doppler (2)
- Continuous Wave Doppler Receiver Function
- Pulse Wave vs Continuous Wave Doppler
- Dangers of Ultrasound
- Slide 137
- Slide 138
- Slide 139
- Ultrasound Terminology
- PZT is Most Common Piezoelectric Material
-
Doppler SensingOnly flow parallel to sound
sensed by scanner
Flow parallel to
sound
Flow perpendicular to sound
Doppler Sensing
Sensed flow always lt actual flow
Sensed flow
Actual flow
Doppler Sensing
ndash cos(q) = SF AF
Sensed flow
(SF)
Actual flow
(AF)q
q
Doppler Equation
bull wherefD =Doppler Shift in MHzfe = echo of reflected frequency (MHz)fo = operating frequency (MHz)v = reflector speed (ms)q = angle between flow amp sound propagationc = speed of sound in soft tissue (ms)
2 X fo X v X cosqf D = fe - fo------------------------- =
cq
Relationships
bull positive shift when reflector moving toward transducerndash echoed frequency gt operating frequency
bull negative shift when reflector moving away from transducerndash echoed frequency lt operating frequency
2 X fo X v X cosqf D = fe - fo------------------------- =
c
q
q
Relationships
bull Doppler angle affects measured Doppler shift
2 X fo X v X cosqf D = fe - fo------------------------- =
c
q
q
cosq
Doppler Relationships
bull higher reflector speed results in greater Doppler shift
bull higher operating frequency results in greater Doppler shift
bull larger Doppler angle results in lower Doppler shift
q 77 X fD (kHz)
v (cms)-------------------------- = fo (MHz) X cosq
Continuous Wave Doppler
bull Audio presentation onlybull No imagebull Useful as fetal dose monitor
Continuous Wave Doppler
bull 2 transducers usedndash one continuously transmits
bull voltage frequency = transducerrsquos operating frequency
ndash typically 2-10 MHz
ndash one continuously receivesbull Reception Area
ndash flow detected within overlap of transmit amp receive sound beams
Continuous Wave DopplerReceiver Function
bull receives reflected sound wavesbull Subtract signals
ndash detects frequency shiftndash typical shift ~ 11000 th of source frequency
bull usually in audible sound range
bull Amplify subtracted signalbull Play directly on speaker
- =
Pulse Wave vs Continuous Wave Doppler
Continuous Wave Pulse Wave
No Image Image
Sound on continuously
Both imaging amp Doppler sound pulses generated
Dangers of Ultrasound
bullThere have been many concerns about the safety of ultrasound
ndashBecause ultrasound is energy the question becomes What is this energy doing to my tissues
or my baby
bullThere have been some reports of low birthweight babies being born to mothers who
had frequent ultrasound examinations during pregnancy
bullThe two major possibilities with ultrasound are as follows
ndashdevelopment of heat - tissues or water absorb the ultrasound energy which increases their
temperature locally ndashformation of bubbles (cavitation) - when dissolved
gases come out of solution due to local heat caused by ultrasound
bullHowever there have been no substantiated ill-effects of ultrasound documented in studies in
either humans or animals ndashThis being said ultrasound should still be used
only when necessary (ie better to be cautious)
Ultrasound Terminology
bull Impedance resistancebull steered
PZT is Most Common Piezoelectric Material
bullLead Zirconate TitanatebullAdvantages
ndashEfficientbullMore electrical energy transferred to sound amp vice-versa
ndashHigh natural resonance frequencyndashRepeatable characteristics
bullStable designbullDisadvantages
ndashHigh acoustic impedancebullCan cause poor acoustic couplingbullRequires matching layer to compensate
- UltarSound Machine Dr Fadhl Alakwaa
- What are the first things to account when purchasing new US equ
- EXCELLENT RESOURCES
- CLINICAL APPLICATIONS
- Slide 5
- Slide 6
- Slide 7
- What do you need to know to be professional in US
- Advantage of US OVER other modalities
- US development
- Slide 11
- What is Ultrasound machine
- Spectrum of sound
- Sound propagation
- Slide 15
- Wave propagation
- Difference between EM and sound
- How to produce sound wave
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Sound field
- Slide 26
- Transducer array
- Slide 28
- Ultrasound Display
- Real-time Scanning
- Linear Curved linear array Phased arraysector Endocavitary
- Transducer Arrays
- Electronic Scanning
- Electrical Scanning
- Linear Array Scanning
- Linear Switched Arrays
- Linear Switched Arrays (2)
- Linear Phased Array
- Linear Phased Array (2)
- Linear Phased Array (3)
- Linear Phased Array (4)
- Linear Phased Array (5)
- Linear Phased Array (6)
- Listening Mode
- 15 Transducer
- 15 amp 2D Transducers
- Remember me to explain why we use the backing block and matchin
- What we will use the returned or received ultrasound waves ldquoech
- Perpendicular Incidence
- Oblique Incidence
- Perpendicular Incidence (2)
- Perpendicular Incidence (3)
- Intensity Reflection Coefficient (IRC) amp Intensity Transmission
- IRC Equation
- Reflections
- Why Use Gel and matching layer
- Slide 57
- THE BASICS US IDEA
- What does your scanner know about echoed sound
- What Does Your Scanner Assume about Echoes (or how the scanner
- Distance of Echo from Transducer
- What is the Speed of Sound
- So the scanner assumes the wrong speed
- Attenuation Correction
- Gray Shade of Echo
- How does scanner know what gray shade to assign an echo
- How to reconstruct the image from echoes
- M Mode
- M-Mode (left ventricle)
- Scanner Processing of Echoes
- Amplification
- Compensation
- Need for Compensation
- Equal Echoes
- Compensation (TGC)
- Compensation (TGC) (2)
- Compression
- Compression (2)
- Demodulation
- Demodulation (2)
- Demodulation Sub-steps
- Rejection
- Rejection (2)
- Image Resolution
- Resolution amp Reflector Size
- Axial Resolution
- Axial Resolution (2)
- Axial Resolution (3)
- Spatial Pulse Length
- Wavelength
- Improve Axial Resolution by Reducing Spatial Pulse Length
- Slide 92
- Lateral Resolution
- Lateral Resolution (2)
- Lateral Resolution (3)
- Contrast Resolution
- Contrast Resolution (2)
- Pre-Processing
- Gray Scale
- Slide 100
- Display Limitations
- Presentation of Brightness Levels
- Slide 103
- Block Diagram
- B Mode
- Color flow imaging (mode) Color Doppler (mode)
- Continuous wave (CW) Doppler
- M-mode
- Power Doppler (mode)
- Pulsed wave Doppler
- Slide 111
- Slide 112
- Slide 113
- Slide 114
- DOPPLER US
- Hemodynamics
- Plug Flow
- Laminar Flow
- Flow
- Flow Pressure amp Resistance
- Doppler Shift
- Doppler Examples
- Doppler Angle
- Flow Components
- Doppler Sensing
- Doppler Sensing (2)
- Doppler Sensing (3)
- Doppler Equation
- Relationships
- Relationships (2)
- Doppler Relationships
- Continuous Wave Doppler
- Continuous Wave Doppler (2)
- Continuous Wave Doppler Receiver Function
- Pulse Wave vs Continuous Wave Doppler
- Dangers of Ultrasound
- Slide 137
- Slide 138
- Slide 139
- Ultrasound Terminology
- PZT is Most Common Piezoelectric Material
-
Doppler Sensing
Sensed flow always lt actual flow
Sensed flow
Actual flow
Doppler Sensing
ndash cos(q) = SF AF
Sensed flow
(SF)
Actual flow
(AF)q
q
Doppler Equation
bull wherefD =Doppler Shift in MHzfe = echo of reflected frequency (MHz)fo = operating frequency (MHz)v = reflector speed (ms)q = angle between flow amp sound propagationc = speed of sound in soft tissue (ms)
2 X fo X v X cosqf D = fe - fo------------------------- =
cq
Relationships
bull positive shift when reflector moving toward transducerndash echoed frequency gt operating frequency
bull negative shift when reflector moving away from transducerndash echoed frequency lt operating frequency
2 X fo X v X cosqf D = fe - fo------------------------- =
c
q
q
Relationships
bull Doppler angle affects measured Doppler shift
2 X fo X v X cosqf D = fe - fo------------------------- =
c
q
q
cosq
Doppler Relationships
bull higher reflector speed results in greater Doppler shift
bull higher operating frequency results in greater Doppler shift
bull larger Doppler angle results in lower Doppler shift
q 77 X fD (kHz)
v (cms)-------------------------- = fo (MHz) X cosq
Continuous Wave Doppler
bull Audio presentation onlybull No imagebull Useful as fetal dose monitor
Continuous Wave Doppler
bull 2 transducers usedndash one continuously transmits
bull voltage frequency = transducerrsquos operating frequency
ndash typically 2-10 MHz
ndash one continuously receivesbull Reception Area
ndash flow detected within overlap of transmit amp receive sound beams
Continuous Wave DopplerReceiver Function
bull receives reflected sound wavesbull Subtract signals
ndash detects frequency shiftndash typical shift ~ 11000 th of source frequency
bull usually in audible sound range
bull Amplify subtracted signalbull Play directly on speaker
- =
Pulse Wave vs Continuous Wave Doppler
Continuous Wave Pulse Wave
No Image Image
Sound on continuously
Both imaging amp Doppler sound pulses generated
Dangers of Ultrasound
bullThere have been many concerns about the safety of ultrasound
ndashBecause ultrasound is energy the question becomes What is this energy doing to my tissues
or my baby
bullThere have been some reports of low birthweight babies being born to mothers who
had frequent ultrasound examinations during pregnancy
bullThe two major possibilities with ultrasound are as follows
ndashdevelopment of heat - tissues or water absorb the ultrasound energy which increases their
temperature locally ndashformation of bubbles (cavitation) - when dissolved
gases come out of solution due to local heat caused by ultrasound
bullHowever there have been no substantiated ill-effects of ultrasound documented in studies in
either humans or animals ndashThis being said ultrasound should still be used
only when necessary (ie better to be cautious)
Ultrasound Terminology
bull Impedance resistancebull steered
PZT is Most Common Piezoelectric Material
bullLead Zirconate TitanatebullAdvantages
ndashEfficientbullMore electrical energy transferred to sound amp vice-versa
ndashHigh natural resonance frequencyndashRepeatable characteristics
bullStable designbullDisadvantages
ndashHigh acoustic impedancebullCan cause poor acoustic couplingbullRequires matching layer to compensate
- UltarSound Machine Dr Fadhl Alakwaa
- What are the first things to account when purchasing new US equ
- EXCELLENT RESOURCES
- CLINICAL APPLICATIONS
- Slide 5
- Slide 6
- Slide 7
- What do you need to know to be professional in US
- Advantage of US OVER other modalities
- US development
- Slide 11
- What is Ultrasound machine
- Spectrum of sound
- Sound propagation
- Slide 15
- Wave propagation
- Difference between EM and sound
- How to produce sound wave
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Sound field
- Slide 26
- Transducer array
- Slide 28
- Ultrasound Display
- Real-time Scanning
- Linear Curved linear array Phased arraysector Endocavitary
- Transducer Arrays
- Electronic Scanning
- Electrical Scanning
- Linear Array Scanning
- Linear Switched Arrays
- Linear Switched Arrays (2)
- Linear Phased Array
- Linear Phased Array (2)
- Linear Phased Array (3)
- Linear Phased Array (4)
- Linear Phased Array (5)
- Linear Phased Array (6)
- Listening Mode
- 15 Transducer
- 15 amp 2D Transducers
- Remember me to explain why we use the backing block and matchin
- What we will use the returned or received ultrasound waves ldquoech
- Perpendicular Incidence
- Oblique Incidence
- Perpendicular Incidence (2)
- Perpendicular Incidence (3)
- Intensity Reflection Coefficient (IRC) amp Intensity Transmission
- IRC Equation
- Reflections
- Why Use Gel and matching layer
- Slide 57
- THE BASICS US IDEA
- What does your scanner know about echoed sound
- What Does Your Scanner Assume about Echoes (or how the scanner
- Distance of Echo from Transducer
- What is the Speed of Sound
- So the scanner assumes the wrong speed
- Attenuation Correction
- Gray Shade of Echo
- How does scanner know what gray shade to assign an echo
- How to reconstruct the image from echoes
- M Mode
- M-Mode (left ventricle)
- Scanner Processing of Echoes
- Amplification
- Compensation
- Need for Compensation
- Equal Echoes
- Compensation (TGC)
- Compensation (TGC) (2)
- Compression
- Compression (2)
- Demodulation
- Demodulation (2)
- Demodulation Sub-steps
- Rejection
- Rejection (2)
- Image Resolution
- Resolution amp Reflector Size
- Axial Resolution
- Axial Resolution (2)
- Axial Resolution (3)
- Spatial Pulse Length
- Wavelength
- Improve Axial Resolution by Reducing Spatial Pulse Length
- Slide 92
- Lateral Resolution
- Lateral Resolution (2)
- Lateral Resolution (3)
- Contrast Resolution
- Contrast Resolution (2)
- Pre-Processing
- Gray Scale
- Slide 100
- Display Limitations
- Presentation of Brightness Levels
- Slide 103
- Block Diagram
- B Mode
- Color flow imaging (mode) Color Doppler (mode)
- Continuous wave (CW) Doppler
- M-mode
- Power Doppler (mode)
- Pulsed wave Doppler
- Slide 111
- Slide 112
- Slide 113
- Slide 114
- DOPPLER US
- Hemodynamics
- Plug Flow
- Laminar Flow
- Flow
- Flow Pressure amp Resistance
- Doppler Shift
- Doppler Examples
- Doppler Angle
- Flow Components
- Doppler Sensing
- Doppler Sensing (2)
- Doppler Sensing (3)
- Doppler Equation
- Relationships
- Relationships (2)
- Doppler Relationships
- Continuous Wave Doppler
- Continuous Wave Doppler (2)
- Continuous Wave Doppler Receiver Function
- Pulse Wave vs Continuous Wave Doppler
- Dangers of Ultrasound
- Slide 137
- Slide 138
- Slide 139
- Ultrasound Terminology
- PZT is Most Common Piezoelectric Material
-
Doppler Sensing
ndash cos(q) = SF AF
Sensed flow
(SF)
Actual flow
(AF)q
q
Doppler Equation
bull wherefD =Doppler Shift in MHzfe = echo of reflected frequency (MHz)fo = operating frequency (MHz)v = reflector speed (ms)q = angle between flow amp sound propagationc = speed of sound in soft tissue (ms)
2 X fo X v X cosqf D = fe - fo------------------------- =
cq
Relationships
bull positive shift when reflector moving toward transducerndash echoed frequency gt operating frequency
bull negative shift when reflector moving away from transducerndash echoed frequency lt operating frequency
2 X fo X v X cosqf D = fe - fo------------------------- =
c
q
q
Relationships
bull Doppler angle affects measured Doppler shift
2 X fo X v X cosqf D = fe - fo------------------------- =
c
q
q
cosq
Doppler Relationships
bull higher reflector speed results in greater Doppler shift
bull higher operating frequency results in greater Doppler shift
bull larger Doppler angle results in lower Doppler shift
q 77 X fD (kHz)
v (cms)-------------------------- = fo (MHz) X cosq
Continuous Wave Doppler
bull Audio presentation onlybull No imagebull Useful as fetal dose monitor
Continuous Wave Doppler
bull 2 transducers usedndash one continuously transmits
bull voltage frequency = transducerrsquos operating frequency
ndash typically 2-10 MHz
ndash one continuously receivesbull Reception Area
ndash flow detected within overlap of transmit amp receive sound beams
Continuous Wave DopplerReceiver Function
bull receives reflected sound wavesbull Subtract signals
ndash detects frequency shiftndash typical shift ~ 11000 th of source frequency
bull usually in audible sound range
bull Amplify subtracted signalbull Play directly on speaker
- =
Pulse Wave vs Continuous Wave Doppler
Continuous Wave Pulse Wave
No Image Image
Sound on continuously
Both imaging amp Doppler sound pulses generated
Dangers of Ultrasound
bullThere have been many concerns about the safety of ultrasound
ndashBecause ultrasound is energy the question becomes What is this energy doing to my tissues
or my baby
bullThere have been some reports of low birthweight babies being born to mothers who
had frequent ultrasound examinations during pregnancy
bullThe two major possibilities with ultrasound are as follows
ndashdevelopment of heat - tissues or water absorb the ultrasound energy which increases their
temperature locally ndashformation of bubbles (cavitation) - when dissolved
gases come out of solution due to local heat caused by ultrasound
bullHowever there have been no substantiated ill-effects of ultrasound documented in studies in
either humans or animals ndashThis being said ultrasound should still be used
only when necessary (ie better to be cautious)
Ultrasound Terminology
bull Impedance resistancebull steered
PZT is Most Common Piezoelectric Material
bullLead Zirconate TitanatebullAdvantages
ndashEfficientbullMore electrical energy transferred to sound amp vice-versa
ndashHigh natural resonance frequencyndashRepeatable characteristics
bullStable designbullDisadvantages
ndashHigh acoustic impedancebullCan cause poor acoustic couplingbullRequires matching layer to compensate
- UltarSound Machine Dr Fadhl Alakwaa
- What are the first things to account when purchasing new US equ
- EXCELLENT RESOURCES
- CLINICAL APPLICATIONS
- Slide 5
- Slide 6
- Slide 7
- What do you need to know to be professional in US
- Advantage of US OVER other modalities
- US development
- Slide 11
- What is Ultrasound machine
- Spectrum of sound
- Sound propagation
- Slide 15
- Wave propagation
- Difference between EM and sound
- How to produce sound wave
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Sound field
- Slide 26
- Transducer array
- Slide 28
- Ultrasound Display
- Real-time Scanning
- Linear Curved linear array Phased arraysector Endocavitary
- Transducer Arrays
- Electronic Scanning
- Electrical Scanning
- Linear Array Scanning
- Linear Switched Arrays
- Linear Switched Arrays (2)
- Linear Phased Array
- Linear Phased Array (2)
- Linear Phased Array (3)
- Linear Phased Array (4)
- Linear Phased Array (5)
- Linear Phased Array (6)
- Listening Mode
- 15 Transducer
- 15 amp 2D Transducers
- Remember me to explain why we use the backing block and matchin
- What we will use the returned or received ultrasound waves ldquoech
- Perpendicular Incidence
- Oblique Incidence
- Perpendicular Incidence (2)
- Perpendicular Incidence (3)
- Intensity Reflection Coefficient (IRC) amp Intensity Transmission
- IRC Equation
- Reflections
- Why Use Gel and matching layer
- Slide 57
- THE BASICS US IDEA
- What does your scanner know about echoed sound
- What Does Your Scanner Assume about Echoes (or how the scanner
- Distance of Echo from Transducer
- What is the Speed of Sound
- So the scanner assumes the wrong speed
- Attenuation Correction
- Gray Shade of Echo
- How does scanner know what gray shade to assign an echo
- How to reconstruct the image from echoes
- M Mode
- M-Mode (left ventricle)
- Scanner Processing of Echoes
- Amplification
- Compensation
- Need for Compensation
- Equal Echoes
- Compensation (TGC)
- Compensation (TGC) (2)
- Compression
- Compression (2)
- Demodulation
- Demodulation (2)
- Demodulation Sub-steps
- Rejection
- Rejection (2)
- Image Resolution
- Resolution amp Reflector Size
- Axial Resolution
- Axial Resolution (2)
- Axial Resolution (3)
- Spatial Pulse Length
- Wavelength
- Improve Axial Resolution by Reducing Spatial Pulse Length
- Slide 92
- Lateral Resolution
- Lateral Resolution (2)
- Lateral Resolution (3)
- Contrast Resolution
- Contrast Resolution (2)
- Pre-Processing
- Gray Scale
- Slide 100
- Display Limitations
- Presentation of Brightness Levels
- Slide 103
- Block Diagram
- B Mode
- Color flow imaging (mode) Color Doppler (mode)
- Continuous wave (CW) Doppler
- M-mode
- Power Doppler (mode)
- Pulsed wave Doppler
- Slide 111
- Slide 112
- Slide 113
- Slide 114
- DOPPLER US
- Hemodynamics
- Plug Flow
- Laminar Flow
- Flow
- Flow Pressure amp Resistance
- Doppler Shift
- Doppler Examples
- Doppler Angle
- Flow Components
- Doppler Sensing
- Doppler Sensing (2)
- Doppler Sensing (3)
- Doppler Equation
- Relationships
- Relationships (2)
- Doppler Relationships
- Continuous Wave Doppler
- Continuous Wave Doppler (2)
- Continuous Wave Doppler Receiver Function
- Pulse Wave vs Continuous Wave Doppler
- Dangers of Ultrasound
- Slide 137
- Slide 138
- Slide 139
- Ultrasound Terminology
- PZT is Most Common Piezoelectric Material
-
Doppler Equation
bull wherefD =Doppler Shift in MHzfe = echo of reflected frequency (MHz)fo = operating frequency (MHz)v = reflector speed (ms)q = angle between flow amp sound propagationc = speed of sound in soft tissue (ms)
2 X fo X v X cosqf D = fe - fo------------------------- =
cq
Relationships
bull positive shift when reflector moving toward transducerndash echoed frequency gt operating frequency
bull negative shift when reflector moving away from transducerndash echoed frequency lt operating frequency
2 X fo X v X cosqf D = fe - fo------------------------- =
c
q
q
Relationships
bull Doppler angle affects measured Doppler shift
2 X fo X v X cosqf D = fe - fo------------------------- =
c
q
q
cosq
Doppler Relationships
bull higher reflector speed results in greater Doppler shift
bull higher operating frequency results in greater Doppler shift
bull larger Doppler angle results in lower Doppler shift
q 77 X fD (kHz)
v (cms)-------------------------- = fo (MHz) X cosq
Continuous Wave Doppler
bull Audio presentation onlybull No imagebull Useful as fetal dose monitor
Continuous Wave Doppler
bull 2 transducers usedndash one continuously transmits
bull voltage frequency = transducerrsquos operating frequency
ndash typically 2-10 MHz
ndash one continuously receivesbull Reception Area
ndash flow detected within overlap of transmit amp receive sound beams
Continuous Wave DopplerReceiver Function
bull receives reflected sound wavesbull Subtract signals
ndash detects frequency shiftndash typical shift ~ 11000 th of source frequency
bull usually in audible sound range
bull Amplify subtracted signalbull Play directly on speaker
- =
Pulse Wave vs Continuous Wave Doppler
Continuous Wave Pulse Wave
No Image Image
Sound on continuously
Both imaging amp Doppler sound pulses generated
Dangers of Ultrasound
bullThere have been many concerns about the safety of ultrasound
ndashBecause ultrasound is energy the question becomes What is this energy doing to my tissues
or my baby
bullThere have been some reports of low birthweight babies being born to mothers who
had frequent ultrasound examinations during pregnancy
bullThe two major possibilities with ultrasound are as follows
ndashdevelopment of heat - tissues or water absorb the ultrasound energy which increases their
temperature locally ndashformation of bubbles (cavitation) - when dissolved
gases come out of solution due to local heat caused by ultrasound
bullHowever there have been no substantiated ill-effects of ultrasound documented in studies in
either humans or animals ndashThis being said ultrasound should still be used
only when necessary (ie better to be cautious)
Ultrasound Terminology
bull Impedance resistancebull steered
PZT is Most Common Piezoelectric Material
bullLead Zirconate TitanatebullAdvantages
ndashEfficientbullMore electrical energy transferred to sound amp vice-versa
ndashHigh natural resonance frequencyndashRepeatable characteristics
bullStable designbullDisadvantages
ndashHigh acoustic impedancebullCan cause poor acoustic couplingbullRequires matching layer to compensate
- UltarSound Machine Dr Fadhl Alakwaa
- What are the first things to account when purchasing new US equ
- EXCELLENT RESOURCES
- CLINICAL APPLICATIONS
- Slide 5
- Slide 6
- Slide 7
- What do you need to know to be professional in US
- Advantage of US OVER other modalities
- US development
- Slide 11
- What is Ultrasound machine
- Spectrum of sound
- Sound propagation
- Slide 15
- Wave propagation
- Difference between EM and sound
- How to produce sound wave
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Sound field
- Slide 26
- Transducer array
- Slide 28
- Ultrasound Display
- Real-time Scanning
- Linear Curved linear array Phased arraysector Endocavitary
- Transducer Arrays
- Electronic Scanning
- Electrical Scanning
- Linear Array Scanning
- Linear Switched Arrays
- Linear Switched Arrays (2)
- Linear Phased Array
- Linear Phased Array (2)
- Linear Phased Array (3)
- Linear Phased Array (4)
- Linear Phased Array (5)
- Linear Phased Array (6)
- Listening Mode
- 15 Transducer
- 15 amp 2D Transducers
- Remember me to explain why we use the backing block and matchin
- What we will use the returned or received ultrasound waves ldquoech
- Perpendicular Incidence
- Oblique Incidence
- Perpendicular Incidence (2)
- Perpendicular Incidence (3)
- Intensity Reflection Coefficient (IRC) amp Intensity Transmission
- IRC Equation
- Reflections
- Why Use Gel and matching layer
- Slide 57
- THE BASICS US IDEA
- What does your scanner know about echoed sound
- What Does Your Scanner Assume about Echoes (or how the scanner
- Distance of Echo from Transducer
- What is the Speed of Sound
- So the scanner assumes the wrong speed
- Attenuation Correction
- Gray Shade of Echo
- How does scanner know what gray shade to assign an echo
- How to reconstruct the image from echoes
- M Mode
- M-Mode (left ventricle)
- Scanner Processing of Echoes
- Amplification
- Compensation
- Need for Compensation
- Equal Echoes
- Compensation (TGC)
- Compensation (TGC) (2)
- Compression
- Compression (2)
- Demodulation
- Demodulation (2)
- Demodulation Sub-steps
- Rejection
- Rejection (2)
- Image Resolution
- Resolution amp Reflector Size
- Axial Resolution
- Axial Resolution (2)
- Axial Resolution (3)
- Spatial Pulse Length
- Wavelength
- Improve Axial Resolution by Reducing Spatial Pulse Length
- Slide 92
- Lateral Resolution
- Lateral Resolution (2)
- Lateral Resolution (3)
- Contrast Resolution
- Contrast Resolution (2)
- Pre-Processing
- Gray Scale
- Slide 100
- Display Limitations
- Presentation of Brightness Levels
- Slide 103
- Block Diagram
- B Mode
- Color flow imaging (mode) Color Doppler (mode)
- Continuous wave (CW) Doppler
- M-mode
- Power Doppler (mode)
- Pulsed wave Doppler
- Slide 111
- Slide 112
- Slide 113
- Slide 114
- DOPPLER US
- Hemodynamics
- Plug Flow
- Laminar Flow
- Flow
- Flow Pressure amp Resistance
- Doppler Shift
- Doppler Examples
- Doppler Angle
- Flow Components
- Doppler Sensing
- Doppler Sensing (2)
- Doppler Sensing (3)
- Doppler Equation
- Relationships
- Relationships (2)
- Doppler Relationships
- Continuous Wave Doppler
- Continuous Wave Doppler (2)
- Continuous Wave Doppler Receiver Function
- Pulse Wave vs Continuous Wave Doppler
- Dangers of Ultrasound
- Slide 137
- Slide 138
- Slide 139
- Ultrasound Terminology
- PZT is Most Common Piezoelectric Material
-
Relationships
bull positive shift when reflector moving toward transducerndash echoed frequency gt operating frequency
bull negative shift when reflector moving away from transducerndash echoed frequency lt operating frequency
2 X fo X v X cosqf D = fe - fo------------------------- =
c
q
q
Relationships
bull Doppler angle affects measured Doppler shift
2 X fo X v X cosqf D = fe - fo------------------------- =
c
q
q
cosq
Doppler Relationships
bull higher reflector speed results in greater Doppler shift
bull higher operating frequency results in greater Doppler shift
bull larger Doppler angle results in lower Doppler shift
q 77 X fD (kHz)
v (cms)-------------------------- = fo (MHz) X cosq
Continuous Wave Doppler
bull Audio presentation onlybull No imagebull Useful as fetal dose monitor
Continuous Wave Doppler
bull 2 transducers usedndash one continuously transmits
bull voltage frequency = transducerrsquos operating frequency
ndash typically 2-10 MHz
ndash one continuously receivesbull Reception Area
ndash flow detected within overlap of transmit amp receive sound beams
Continuous Wave DopplerReceiver Function
bull receives reflected sound wavesbull Subtract signals
ndash detects frequency shiftndash typical shift ~ 11000 th of source frequency
bull usually in audible sound range
bull Amplify subtracted signalbull Play directly on speaker
- =
Pulse Wave vs Continuous Wave Doppler
Continuous Wave Pulse Wave
No Image Image
Sound on continuously
Both imaging amp Doppler sound pulses generated
Dangers of Ultrasound
bullThere have been many concerns about the safety of ultrasound
ndashBecause ultrasound is energy the question becomes What is this energy doing to my tissues
or my baby
bullThere have been some reports of low birthweight babies being born to mothers who
had frequent ultrasound examinations during pregnancy
bullThe two major possibilities with ultrasound are as follows
ndashdevelopment of heat - tissues or water absorb the ultrasound energy which increases their
temperature locally ndashformation of bubbles (cavitation) - when dissolved
gases come out of solution due to local heat caused by ultrasound
bullHowever there have been no substantiated ill-effects of ultrasound documented in studies in
either humans or animals ndashThis being said ultrasound should still be used
only when necessary (ie better to be cautious)
Ultrasound Terminology
bull Impedance resistancebull steered
PZT is Most Common Piezoelectric Material
bullLead Zirconate TitanatebullAdvantages
ndashEfficientbullMore electrical energy transferred to sound amp vice-versa
ndashHigh natural resonance frequencyndashRepeatable characteristics
bullStable designbullDisadvantages
ndashHigh acoustic impedancebullCan cause poor acoustic couplingbullRequires matching layer to compensate
- UltarSound Machine Dr Fadhl Alakwaa
- What are the first things to account when purchasing new US equ
- EXCELLENT RESOURCES
- CLINICAL APPLICATIONS
- Slide 5
- Slide 6
- Slide 7
- What do you need to know to be professional in US
- Advantage of US OVER other modalities
- US development
- Slide 11
- What is Ultrasound machine
- Spectrum of sound
- Sound propagation
- Slide 15
- Wave propagation
- Difference between EM and sound
- How to produce sound wave
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Sound field
- Slide 26
- Transducer array
- Slide 28
- Ultrasound Display
- Real-time Scanning
- Linear Curved linear array Phased arraysector Endocavitary
- Transducer Arrays
- Electronic Scanning
- Electrical Scanning
- Linear Array Scanning
- Linear Switched Arrays
- Linear Switched Arrays (2)
- Linear Phased Array
- Linear Phased Array (2)
- Linear Phased Array (3)
- Linear Phased Array (4)
- Linear Phased Array (5)
- Linear Phased Array (6)
- Listening Mode
- 15 Transducer
- 15 amp 2D Transducers
- Remember me to explain why we use the backing block and matchin
- What we will use the returned or received ultrasound waves ldquoech
- Perpendicular Incidence
- Oblique Incidence
- Perpendicular Incidence (2)
- Perpendicular Incidence (3)
- Intensity Reflection Coefficient (IRC) amp Intensity Transmission
- IRC Equation
- Reflections
- Why Use Gel and matching layer
- Slide 57
- THE BASICS US IDEA
- What does your scanner know about echoed sound
- What Does Your Scanner Assume about Echoes (or how the scanner
- Distance of Echo from Transducer
- What is the Speed of Sound
- So the scanner assumes the wrong speed
- Attenuation Correction
- Gray Shade of Echo
- How does scanner know what gray shade to assign an echo
- How to reconstruct the image from echoes
- M Mode
- M-Mode (left ventricle)
- Scanner Processing of Echoes
- Amplification
- Compensation
- Need for Compensation
- Equal Echoes
- Compensation (TGC)
- Compensation (TGC) (2)
- Compression
- Compression (2)
- Demodulation
- Demodulation (2)
- Demodulation Sub-steps
- Rejection
- Rejection (2)
- Image Resolution
- Resolution amp Reflector Size
- Axial Resolution
- Axial Resolution (2)
- Axial Resolution (3)
- Spatial Pulse Length
- Wavelength
- Improve Axial Resolution by Reducing Spatial Pulse Length
- Slide 92
- Lateral Resolution
- Lateral Resolution (2)
- Lateral Resolution (3)
- Contrast Resolution
- Contrast Resolution (2)
- Pre-Processing
- Gray Scale
- Slide 100
- Display Limitations
- Presentation of Brightness Levels
- Slide 103
- Block Diagram
- B Mode
- Color flow imaging (mode) Color Doppler (mode)
- Continuous wave (CW) Doppler
- M-mode
- Power Doppler (mode)
- Pulsed wave Doppler
- Slide 111
- Slide 112
- Slide 113
- Slide 114
- DOPPLER US
- Hemodynamics
- Plug Flow
- Laminar Flow
- Flow
- Flow Pressure amp Resistance
- Doppler Shift
- Doppler Examples
- Doppler Angle
- Flow Components
- Doppler Sensing
- Doppler Sensing (2)
- Doppler Sensing (3)
- Doppler Equation
- Relationships
- Relationships (2)
- Doppler Relationships
- Continuous Wave Doppler
- Continuous Wave Doppler (2)
- Continuous Wave Doppler Receiver Function
- Pulse Wave vs Continuous Wave Doppler
- Dangers of Ultrasound
- Slide 137
- Slide 138
- Slide 139
- Ultrasound Terminology
- PZT is Most Common Piezoelectric Material
-
Relationships
bull Doppler angle affects measured Doppler shift
2 X fo X v X cosqf D = fe - fo------------------------- =
c
q
q
cosq
Doppler Relationships
bull higher reflector speed results in greater Doppler shift
bull higher operating frequency results in greater Doppler shift
bull larger Doppler angle results in lower Doppler shift
q 77 X fD (kHz)
v (cms)-------------------------- = fo (MHz) X cosq
Continuous Wave Doppler
bull Audio presentation onlybull No imagebull Useful as fetal dose monitor
Continuous Wave Doppler
bull 2 transducers usedndash one continuously transmits
bull voltage frequency = transducerrsquos operating frequency
ndash typically 2-10 MHz
ndash one continuously receivesbull Reception Area
ndash flow detected within overlap of transmit amp receive sound beams
Continuous Wave DopplerReceiver Function
bull receives reflected sound wavesbull Subtract signals
ndash detects frequency shiftndash typical shift ~ 11000 th of source frequency
bull usually in audible sound range
bull Amplify subtracted signalbull Play directly on speaker
- =
Pulse Wave vs Continuous Wave Doppler
Continuous Wave Pulse Wave
No Image Image
Sound on continuously
Both imaging amp Doppler sound pulses generated
Dangers of Ultrasound
bullThere have been many concerns about the safety of ultrasound
ndashBecause ultrasound is energy the question becomes What is this energy doing to my tissues
or my baby
bullThere have been some reports of low birthweight babies being born to mothers who
had frequent ultrasound examinations during pregnancy
bullThe two major possibilities with ultrasound are as follows
ndashdevelopment of heat - tissues or water absorb the ultrasound energy which increases their
temperature locally ndashformation of bubbles (cavitation) - when dissolved
gases come out of solution due to local heat caused by ultrasound
bullHowever there have been no substantiated ill-effects of ultrasound documented in studies in
either humans or animals ndashThis being said ultrasound should still be used
only when necessary (ie better to be cautious)
Ultrasound Terminology
bull Impedance resistancebull steered
PZT is Most Common Piezoelectric Material
bullLead Zirconate TitanatebullAdvantages
ndashEfficientbullMore electrical energy transferred to sound amp vice-versa
ndashHigh natural resonance frequencyndashRepeatable characteristics
bullStable designbullDisadvantages
ndashHigh acoustic impedancebullCan cause poor acoustic couplingbullRequires matching layer to compensate
- UltarSound Machine Dr Fadhl Alakwaa
- What are the first things to account when purchasing new US equ
- EXCELLENT RESOURCES
- CLINICAL APPLICATIONS
- Slide 5
- Slide 6
- Slide 7
- What do you need to know to be professional in US
- Advantage of US OVER other modalities
- US development
- Slide 11
- What is Ultrasound machine
- Spectrum of sound
- Sound propagation
- Slide 15
- Wave propagation
- Difference between EM and sound
- How to produce sound wave
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Sound field
- Slide 26
- Transducer array
- Slide 28
- Ultrasound Display
- Real-time Scanning
- Linear Curved linear array Phased arraysector Endocavitary
- Transducer Arrays
- Electronic Scanning
- Electrical Scanning
- Linear Array Scanning
- Linear Switched Arrays
- Linear Switched Arrays (2)
- Linear Phased Array
- Linear Phased Array (2)
- Linear Phased Array (3)
- Linear Phased Array (4)
- Linear Phased Array (5)
- Linear Phased Array (6)
- Listening Mode
- 15 Transducer
- 15 amp 2D Transducers
- Remember me to explain why we use the backing block and matchin
- What we will use the returned or received ultrasound waves ldquoech
- Perpendicular Incidence
- Oblique Incidence
- Perpendicular Incidence (2)
- Perpendicular Incidence (3)
- Intensity Reflection Coefficient (IRC) amp Intensity Transmission
- IRC Equation
- Reflections
- Why Use Gel and matching layer
- Slide 57
- THE BASICS US IDEA
- What does your scanner know about echoed sound
- What Does Your Scanner Assume about Echoes (or how the scanner
- Distance of Echo from Transducer
- What is the Speed of Sound
- So the scanner assumes the wrong speed
- Attenuation Correction
- Gray Shade of Echo
- How does scanner know what gray shade to assign an echo
- How to reconstruct the image from echoes
- M Mode
- M-Mode (left ventricle)
- Scanner Processing of Echoes
- Amplification
- Compensation
- Need for Compensation
- Equal Echoes
- Compensation (TGC)
- Compensation (TGC) (2)
- Compression
- Compression (2)
- Demodulation
- Demodulation (2)
- Demodulation Sub-steps
- Rejection
- Rejection (2)
- Image Resolution
- Resolution amp Reflector Size
- Axial Resolution
- Axial Resolution (2)
- Axial Resolution (3)
- Spatial Pulse Length
- Wavelength
- Improve Axial Resolution by Reducing Spatial Pulse Length
- Slide 92
- Lateral Resolution
- Lateral Resolution (2)
- Lateral Resolution (3)
- Contrast Resolution
- Contrast Resolution (2)
- Pre-Processing
- Gray Scale
- Slide 100
- Display Limitations
- Presentation of Brightness Levels
- Slide 103
- Block Diagram
- B Mode
- Color flow imaging (mode) Color Doppler (mode)
- Continuous wave (CW) Doppler
- M-mode
- Power Doppler (mode)
- Pulsed wave Doppler
- Slide 111
- Slide 112
- Slide 113
- Slide 114
- DOPPLER US
- Hemodynamics
- Plug Flow
- Laminar Flow
- Flow
- Flow Pressure amp Resistance
- Doppler Shift
- Doppler Examples
- Doppler Angle
- Flow Components
- Doppler Sensing
- Doppler Sensing (2)
- Doppler Sensing (3)
- Doppler Equation
- Relationships
- Relationships (2)
- Doppler Relationships
- Continuous Wave Doppler
- Continuous Wave Doppler (2)
- Continuous Wave Doppler Receiver Function
- Pulse Wave vs Continuous Wave Doppler
- Dangers of Ultrasound
- Slide 137
- Slide 138
- Slide 139
- Ultrasound Terminology
- PZT is Most Common Piezoelectric Material
-
Doppler Relationships
bull higher reflector speed results in greater Doppler shift
bull higher operating frequency results in greater Doppler shift
bull larger Doppler angle results in lower Doppler shift
q 77 X fD (kHz)
v (cms)-------------------------- = fo (MHz) X cosq
Continuous Wave Doppler
bull Audio presentation onlybull No imagebull Useful as fetal dose monitor
Continuous Wave Doppler
bull 2 transducers usedndash one continuously transmits
bull voltage frequency = transducerrsquos operating frequency
ndash typically 2-10 MHz
ndash one continuously receivesbull Reception Area
ndash flow detected within overlap of transmit amp receive sound beams
Continuous Wave DopplerReceiver Function
bull receives reflected sound wavesbull Subtract signals
ndash detects frequency shiftndash typical shift ~ 11000 th of source frequency
bull usually in audible sound range
bull Amplify subtracted signalbull Play directly on speaker
- =
Pulse Wave vs Continuous Wave Doppler
Continuous Wave Pulse Wave
No Image Image
Sound on continuously
Both imaging amp Doppler sound pulses generated
Dangers of Ultrasound
bullThere have been many concerns about the safety of ultrasound
ndashBecause ultrasound is energy the question becomes What is this energy doing to my tissues
or my baby
bullThere have been some reports of low birthweight babies being born to mothers who
had frequent ultrasound examinations during pregnancy
bullThe two major possibilities with ultrasound are as follows
ndashdevelopment of heat - tissues or water absorb the ultrasound energy which increases their
temperature locally ndashformation of bubbles (cavitation) - when dissolved
gases come out of solution due to local heat caused by ultrasound
bullHowever there have been no substantiated ill-effects of ultrasound documented in studies in
either humans or animals ndashThis being said ultrasound should still be used
only when necessary (ie better to be cautious)
Ultrasound Terminology
bull Impedance resistancebull steered
PZT is Most Common Piezoelectric Material
bullLead Zirconate TitanatebullAdvantages
ndashEfficientbullMore electrical energy transferred to sound amp vice-versa
ndashHigh natural resonance frequencyndashRepeatable characteristics
bullStable designbullDisadvantages
ndashHigh acoustic impedancebullCan cause poor acoustic couplingbullRequires matching layer to compensate
- UltarSound Machine Dr Fadhl Alakwaa
- What are the first things to account when purchasing new US equ
- EXCELLENT RESOURCES
- CLINICAL APPLICATIONS
- Slide 5
- Slide 6
- Slide 7
- What do you need to know to be professional in US
- Advantage of US OVER other modalities
- US development
- Slide 11
- What is Ultrasound machine
- Spectrum of sound
- Sound propagation
- Slide 15
- Wave propagation
- Difference between EM and sound
- How to produce sound wave
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Sound field
- Slide 26
- Transducer array
- Slide 28
- Ultrasound Display
- Real-time Scanning
- Linear Curved linear array Phased arraysector Endocavitary
- Transducer Arrays
- Electronic Scanning
- Electrical Scanning
- Linear Array Scanning
- Linear Switched Arrays
- Linear Switched Arrays (2)
- Linear Phased Array
- Linear Phased Array (2)
- Linear Phased Array (3)
- Linear Phased Array (4)
- Linear Phased Array (5)
- Linear Phased Array (6)
- Listening Mode
- 15 Transducer
- 15 amp 2D Transducers
- Remember me to explain why we use the backing block and matchin
- What we will use the returned or received ultrasound waves ldquoech
- Perpendicular Incidence
- Oblique Incidence
- Perpendicular Incidence (2)
- Perpendicular Incidence (3)
- Intensity Reflection Coefficient (IRC) amp Intensity Transmission
- IRC Equation
- Reflections
- Why Use Gel and matching layer
- Slide 57
- THE BASICS US IDEA
- What does your scanner know about echoed sound
- What Does Your Scanner Assume about Echoes (or how the scanner
- Distance of Echo from Transducer
- What is the Speed of Sound
- So the scanner assumes the wrong speed
- Attenuation Correction
- Gray Shade of Echo
- How does scanner know what gray shade to assign an echo
- How to reconstruct the image from echoes
- M Mode
- M-Mode (left ventricle)
- Scanner Processing of Echoes
- Amplification
- Compensation
- Need for Compensation
- Equal Echoes
- Compensation (TGC)
- Compensation (TGC) (2)
- Compression
- Compression (2)
- Demodulation
- Demodulation (2)
- Demodulation Sub-steps
- Rejection
- Rejection (2)
- Image Resolution
- Resolution amp Reflector Size
- Axial Resolution
- Axial Resolution (2)
- Axial Resolution (3)
- Spatial Pulse Length
- Wavelength
- Improve Axial Resolution by Reducing Spatial Pulse Length
- Slide 92
- Lateral Resolution
- Lateral Resolution (2)
- Lateral Resolution (3)
- Contrast Resolution
- Contrast Resolution (2)
- Pre-Processing
- Gray Scale
- Slide 100
- Display Limitations
- Presentation of Brightness Levels
- Slide 103
- Block Diagram
- B Mode
- Color flow imaging (mode) Color Doppler (mode)
- Continuous wave (CW) Doppler
- M-mode
- Power Doppler (mode)
- Pulsed wave Doppler
- Slide 111
- Slide 112
- Slide 113
- Slide 114
- DOPPLER US
- Hemodynamics
- Plug Flow
- Laminar Flow
- Flow
- Flow Pressure amp Resistance
- Doppler Shift
- Doppler Examples
- Doppler Angle
- Flow Components
- Doppler Sensing
- Doppler Sensing (2)
- Doppler Sensing (3)
- Doppler Equation
- Relationships
- Relationships (2)
- Doppler Relationships
- Continuous Wave Doppler
- Continuous Wave Doppler (2)
- Continuous Wave Doppler Receiver Function
- Pulse Wave vs Continuous Wave Doppler
- Dangers of Ultrasound
- Slide 137
- Slide 138
- Slide 139
- Ultrasound Terminology
- PZT is Most Common Piezoelectric Material
-
Continuous Wave Doppler
bull Audio presentation onlybull No imagebull Useful as fetal dose monitor
Continuous Wave Doppler
bull 2 transducers usedndash one continuously transmits
bull voltage frequency = transducerrsquos operating frequency
ndash typically 2-10 MHz
ndash one continuously receivesbull Reception Area
ndash flow detected within overlap of transmit amp receive sound beams
Continuous Wave DopplerReceiver Function
bull receives reflected sound wavesbull Subtract signals
ndash detects frequency shiftndash typical shift ~ 11000 th of source frequency
bull usually in audible sound range
bull Amplify subtracted signalbull Play directly on speaker
- =
Pulse Wave vs Continuous Wave Doppler
Continuous Wave Pulse Wave
No Image Image
Sound on continuously
Both imaging amp Doppler sound pulses generated
Dangers of Ultrasound
bullThere have been many concerns about the safety of ultrasound
ndashBecause ultrasound is energy the question becomes What is this energy doing to my tissues
or my baby
bullThere have been some reports of low birthweight babies being born to mothers who
had frequent ultrasound examinations during pregnancy
bullThe two major possibilities with ultrasound are as follows
ndashdevelopment of heat - tissues or water absorb the ultrasound energy which increases their
temperature locally ndashformation of bubbles (cavitation) - when dissolved
gases come out of solution due to local heat caused by ultrasound
bullHowever there have been no substantiated ill-effects of ultrasound documented in studies in
either humans or animals ndashThis being said ultrasound should still be used
only when necessary (ie better to be cautious)
Ultrasound Terminology
bull Impedance resistancebull steered
PZT is Most Common Piezoelectric Material
bullLead Zirconate TitanatebullAdvantages
ndashEfficientbullMore electrical energy transferred to sound amp vice-versa
ndashHigh natural resonance frequencyndashRepeatable characteristics
bullStable designbullDisadvantages
ndashHigh acoustic impedancebullCan cause poor acoustic couplingbullRequires matching layer to compensate
- UltarSound Machine Dr Fadhl Alakwaa
- What are the first things to account when purchasing new US equ
- EXCELLENT RESOURCES
- CLINICAL APPLICATIONS
- Slide 5
- Slide 6
- Slide 7
- What do you need to know to be professional in US
- Advantage of US OVER other modalities
- US development
- Slide 11
- What is Ultrasound machine
- Spectrum of sound
- Sound propagation
- Slide 15
- Wave propagation
- Difference between EM and sound
- How to produce sound wave
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Sound field
- Slide 26
- Transducer array
- Slide 28
- Ultrasound Display
- Real-time Scanning
- Linear Curved linear array Phased arraysector Endocavitary
- Transducer Arrays
- Electronic Scanning
- Electrical Scanning
- Linear Array Scanning
- Linear Switched Arrays
- Linear Switched Arrays (2)
- Linear Phased Array
- Linear Phased Array (2)
- Linear Phased Array (3)
- Linear Phased Array (4)
- Linear Phased Array (5)
- Linear Phased Array (6)
- Listening Mode
- 15 Transducer
- 15 amp 2D Transducers
- Remember me to explain why we use the backing block and matchin
- What we will use the returned or received ultrasound waves ldquoech
- Perpendicular Incidence
- Oblique Incidence
- Perpendicular Incidence (2)
- Perpendicular Incidence (3)
- Intensity Reflection Coefficient (IRC) amp Intensity Transmission
- IRC Equation
- Reflections
- Why Use Gel and matching layer
- Slide 57
- THE BASICS US IDEA
- What does your scanner know about echoed sound
- What Does Your Scanner Assume about Echoes (or how the scanner
- Distance of Echo from Transducer
- What is the Speed of Sound
- So the scanner assumes the wrong speed
- Attenuation Correction
- Gray Shade of Echo
- How does scanner know what gray shade to assign an echo
- How to reconstruct the image from echoes
- M Mode
- M-Mode (left ventricle)
- Scanner Processing of Echoes
- Amplification
- Compensation
- Need for Compensation
- Equal Echoes
- Compensation (TGC)
- Compensation (TGC) (2)
- Compression
- Compression (2)
- Demodulation
- Demodulation (2)
- Demodulation Sub-steps
- Rejection
- Rejection (2)
- Image Resolution
- Resolution amp Reflector Size
- Axial Resolution
- Axial Resolution (2)
- Axial Resolution (3)
- Spatial Pulse Length
- Wavelength
- Improve Axial Resolution by Reducing Spatial Pulse Length
- Slide 92
- Lateral Resolution
- Lateral Resolution (2)
- Lateral Resolution (3)
- Contrast Resolution
- Contrast Resolution (2)
- Pre-Processing
- Gray Scale
- Slide 100
- Display Limitations
- Presentation of Brightness Levels
- Slide 103
- Block Diagram
- B Mode
- Color flow imaging (mode) Color Doppler (mode)
- Continuous wave (CW) Doppler
- M-mode
- Power Doppler (mode)
- Pulsed wave Doppler
- Slide 111
- Slide 112
- Slide 113
- Slide 114
- DOPPLER US
- Hemodynamics
- Plug Flow
- Laminar Flow
- Flow
- Flow Pressure amp Resistance
- Doppler Shift
- Doppler Examples
- Doppler Angle
- Flow Components
- Doppler Sensing
- Doppler Sensing (2)
- Doppler Sensing (3)
- Doppler Equation
- Relationships
- Relationships (2)
- Doppler Relationships
- Continuous Wave Doppler
- Continuous Wave Doppler (2)
- Continuous Wave Doppler Receiver Function
- Pulse Wave vs Continuous Wave Doppler
- Dangers of Ultrasound
- Slide 137
- Slide 138
- Slide 139
- Ultrasound Terminology
- PZT is Most Common Piezoelectric Material
-
Continuous Wave Doppler
bull 2 transducers usedndash one continuously transmits
bull voltage frequency = transducerrsquos operating frequency
ndash typically 2-10 MHz
ndash one continuously receivesbull Reception Area
ndash flow detected within overlap of transmit amp receive sound beams
Continuous Wave DopplerReceiver Function
bull receives reflected sound wavesbull Subtract signals
ndash detects frequency shiftndash typical shift ~ 11000 th of source frequency
bull usually in audible sound range
bull Amplify subtracted signalbull Play directly on speaker
- =
Pulse Wave vs Continuous Wave Doppler
Continuous Wave Pulse Wave
No Image Image
Sound on continuously
Both imaging amp Doppler sound pulses generated
Dangers of Ultrasound
bullThere have been many concerns about the safety of ultrasound
ndashBecause ultrasound is energy the question becomes What is this energy doing to my tissues
or my baby
bullThere have been some reports of low birthweight babies being born to mothers who
had frequent ultrasound examinations during pregnancy
bullThe two major possibilities with ultrasound are as follows
ndashdevelopment of heat - tissues or water absorb the ultrasound energy which increases their
temperature locally ndashformation of bubbles (cavitation) - when dissolved
gases come out of solution due to local heat caused by ultrasound
bullHowever there have been no substantiated ill-effects of ultrasound documented in studies in
either humans or animals ndashThis being said ultrasound should still be used
only when necessary (ie better to be cautious)
Ultrasound Terminology
bull Impedance resistancebull steered
PZT is Most Common Piezoelectric Material
bullLead Zirconate TitanatebullAdvantages
ndashEfficientbullMore electrical energy transferred to sound amp vice-versa
ndashHigh natural resonance frequencyndashRepeatable characteristics
bullStable designbullDisadvantages
ndashHigh acoustic impedancebullCan cause poor acoustic couplingbullRequires matching layer to compensate
- UltarSound Machine Dr Fadhl Alakwaa
- What are the first things to account when purchasing new US equ
- EXCELLENT RESOURCES
- CLINICAL APPLICATIONS
- Slide 5
- Slide 6
- Slide 7
- What do you need to know to be professional in US
- Advantage of US OVER other modalities
- US development
- Slide 11
- What is Ultrasound machine
- Spectrum of sound
- Sound propagation
- Slide 15
- Wave propagation
- Difference between EM and sound
- How to produce sound wave
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Sound field
- Slide 26
- Transducer array
- Slide 28
- Ultrasound Display
- Real-time Scanning
- Linear Curved linear array Phased arraysector Endocavitary
- Transducer Arrays
- Electronic Scanning
- Electrical Scanning
- Linear Array Scanning
- Linear Switched Arrays
- Linear Switched Arrays (2)
- Linear Phased Array
- Linear Phased Array (2)
- Linear Phased Array (3)
- Linear Phased Array (4)
- Linear Phased Array (5)
- Linear Phased Array (6)
- Listening Mode
- 15 Transducer
- 15 amp 2D Transducers
- Remember me to explain why we use the backing block and matchin
- What we will use the returned or received ultrasound waves ldquoech
- Perpendicular Incidence
- Oblique Incidence
- Perpendicular Incidence (2)
- Perpendicular Incidence (3)
- Intensity Reflection Coefficient (IRC) amp Intensity Transmission
- IRC Equation
- Reflections
- Why Use Gel and matching layer
- Slide 57
- THE BASICS US IDEA
- What does your scanner know about echoed sound
- What Does Your Scanner Assume about Echoes (or how the scanner
- Distance of Echo from Transducer
- What is the Speed of Sound
- So the scanner assumes the wrong speed
- Attenuation Correction
- Gray Shade of Echo
- How does scanner know what gray shade to assign an echo
- How to reconstruct the image from echoes
- M Mode
- M-Mode (left ventricle)
- Scanner Processing of Echoes
- Amplification
- Compensation
- Need for Compensation
- Equal Echoes
- Compensation (TGC)
- Compensation (TGC) (2)
- Compression
- Compression (2)
- Demodulation
- Demodulation (2)
- Demodulation Sub-steps
- Rejection
- Rejection (2)
- Image Resolution
- Resolution amp Reflector Size
- Axial Resolution
- Axial Resolution (2)
- Axial Resolution (3)
- Spatial Pulse Length
- Wavelength
- Improve Axial Resolution by Reducing Spatial Pulse Length
- Slide 92
- Lateral Resolution
- Lateral Resolution (2)
- Lateral Resolution (3)
- Contrast Resolution
- Contrast Resolution (2)
- Pre-Processing
- Gray Scale
- Slide 100
- Display Limitations
- Presentation of Brightness Levels
- Slide 103
- Block Diagram
- B Mode
- Color flow imaging (mode) Color Doppler (mode)
- Continuous wave (CW) Doppler
- M-mode
- Power Doppler (mode)
- Pulsed wave Doppler
- Slide 111
- Slide 112
- Slide 113
- Slide 114
- DOPPLER US
- Hemodynamics
- Plug Flow
- Laminar Flow
- Flow
- Flow Pressure amp Resistance
- Doppler Shift
- Doppler Examples
- Doppler Angle
- Flow Components
- Doppler Sensing
- Doppler Sensing (2)
- Doppler Sensing (3)
- Doppler Equation
- Relationships
- Relationships (2)
- Doppler Relationships
- Continuous Wave Doppler
- Continuous Wave Doppler (2)
- Continuous Wave Doppler Receiver Function
- Pulse Wave vs Continuous Wave Doppler
- Dangers of Ultrasound
- Slide 137
- Slide 138
- Slide 139
- Ultrasound Terminology
- PZT is Most Common Piezoelectric Material
-
Continuous Wave DopplerReceiver Function
bull receives reflected sound wavesbull Subtract signals
ndash detects frequency shiftndash typical shift ~ 11000 th of source frequency
bull usually in audible sound range
bull Amplify subtracted signalbull Play directly on speaker
- =
Pulse Wave vs Continuous Wave Doppler
Continuous Wave Pulse Wave
No Image Image
Sound on continuously
Both imaging amp Doppler sound pulses generated
Dangers of Ultrasound
bullThere have been many concerns about the safety of ultrasound
ndashBecause ultrasound is energy the question becomes What is this energy doing to my tissues
or my baby
bullThere have been some reports of low birthweight babies being born to mothers who
had frequent ultrasound examinations during pregnancy
bullThe two major possibilities with ultrasound are as follows
ndashdevelopment of heat - tissues or water absorb the ultrasound energy which increases their
temperature locally ndashformation of bubbles (cavitation) - when dissolved
gases come out of solution due to local heat caused by ultrasound
bullHowever there have been no substantiated ill-effects of ultrasound documented in studies in
either humans or animals ndashThis being said ultrasound should still be used
only when necessary (ie better to be cautious)
Ultrasound Terminology
bull Impedance resistancebull steered
PZT is Most Common Piezoelectric Material
bullLead Zirconate TitanatebullAdvantages
ndashEfficientbullMore electrical energy transferred to sound amp vice-versa
ndashHigh natural resonance frequencyndashRepeatable characteristics
bullStable designbullDisadvantages
ndashHigh acoustic impedancebullCan cause poor acoustic couplingbullRequires matching layer to compensate
- UltarSound Machine Dr Fadhl Alakwaa
- What are the first things to account when purchasing new US equ
- EXCELLENT RESOURCES
- CLINICAL APPLICATIONS
- Slide 5
- Slide 6
- Slide 7
- What do you need to know to be professional in US
- Advantage of US OVER other modalities
- US development
- Slide 11
- What is Ultrasound machine
- Spectrum of sound
- Sound propagation
- Slide 15
- Wave propagation
- Difference between EM and sound
- How to produce sound wave
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Sound field
- Slide 26
- Transducer array
- Slide 28
- Ultrasound Display
- Real-time Scanning
- Linear Curved linear array Phased arraysector Endocavitary
- Transducer Arrays
- Electronic Scanning
- Electrical Scanning
- Linear Array Scanning
- Linear Switched Arrays
- Linear Switched Arrays (2)
- Linear Phased Array
- Linear Phased Array (2)
- Linear Phased Array (3)
- Linear Phased Array (4)
- Linear Phased Array (5)
- Linear Phased Array (6)
- Listening Mode
- 15 Transducer
- 15 amp 2D Transducers
- Remember me to explain why we use the backing block and matchin
- What we will use the returned or received ultrasound waves ldquoech
- Perpendicular Incidence
- Oblique Incidence
- Perpendicular Incidence (2)
- Perpendicular Incidence (3)
- Intensity Reflection Coefficient (IRC) amp Intensity Transmission
- IRC Equation
- Reflections
- Why Use Gel and matching layer
- Slide 57
- THE BASICS US IDEA
- What does your scanner know about echoed sound
- What Does Your Scanner Assume about Echoes (or how the scanner
- Distance of Echo from Transducer
- What is the Speed of Sound
- So the scanner assumes the wrong speed
- Attenuation Correction
- Gray Shade of Echo
- How does scanner know what gray shade to assign an echo
- How to reconstruct the image from echoes
- M Mode
- M-Mode (left ventricle)
- Scanner Processing of Echoes
- Amplification
- Compensation
- Need for Compensation
- Equal Echoes
- Compensation (TGC)
- Compensation (TGC) (2)
- Compression
- Compression (2)
- Demodulation
- Demodulation (2)
- Demodulation Sub-steps
- Rejection
- Rejection (2)
- Image Resolution
- Resolution amp Reflector Size
- Axial Resolution
- Axial Resolution (2)
- Axial Resolution (3)
- Spatial Pulse Length
- Wavelength
- Improve Axial Resolution by Reducing Spatial Pulse Length
- Slide 92
- Lateral Resolution
- Lateral Resolution (2)
- Lateral Resolution (3)
- Contrast Resolution
- Contrast Resolution (2)
- Pre-Processing
- Gray Scale
- Slide 100
- Display Limitations
- Presentation of Brightness Levels
- Slide 103
- Block Diagram
- B Mode
- Color flow imaging (mode) Color Doppler (mode)
- Continuous wave (CW) Doppler
- M-mode
- Power Doppler (mode)
- Pulsed wave Doppler
- Slide 111
- Slide 112
- Slide 113
- Slide 114
- DOPPLER US
- Hemodynamics
- Plug Flow
- Laminar Flow
- Flow
- Flow Pressure amp Resistance
- Doppler Shift
- Doppler Examples
- Doppler Angle
- Flow Components
- Doppler Sensing
- Doppler Sensing (2)
- Doppler Sensing (3)
- Doppler Equation
- Relationships
- Relationships (2)
- Doppler Relationships
- Continuous Wave Doppler
- Continuous Wave Doppler (2)
- Continuous Wave Doppler Receiver Function
- Pulse Wave vs Continuous Wave Doppler
- Dangers of Ultrasound
- Slide 137
- Slide 138
- Slide 139
- Ultrasound Terminology
- PZT is Most Common Piezoelectric Material
-
Pulse Wave vs Continuous Wave Doppler
Continuous Wave Pulse Wave
No Image Image
Sound on continuously
Both imaging amp Doppler sound pulses generated
Dangers of Ultrasound
bullThere have been many concerns about the safety of ultrasound
ndashBecause ultrasound is energy the question becomes What is this energy doing to my tissues
or my baby
bullThere have been some reports of low birthweight babies being born to mothers who
had frequent ultrasound examinations during pregnancy
bullThe two major possibilities with ultrasound are as follows
ndashdevelopment of heat - tissues or water absorb the ultrasound energy which increases their
temperature locally ndashformation of bubbles (cavitation) - when dissolved
gases come out of solution due to local heat caused by ultrasound
bullHowever there have been no substantiated ill-effects of ultrasound documented in studies in
either humans or animals ndashThis being said ultrasound should still be used
only when necessary (ie better to be cautious)
Ultrasound Terminology
bull Impedance resistancebull steered
PZT is Most Common Piezoelectric Material
bullLead Zirconate TitanatebullAdvantages
ndashEfficientbullMore electrical energy transferred to sound amp vice-versa
ndashHigh natural resonance frequencyndashRepeatable characteristics
bullStable designbullDisadvantages
ndashHigh acoustic impedancebullCan cause poor acoustic couplingbullRequires matching layer to compensate
- UltarSound Machine Dr Fadhl Alakwaa
- What are the first things to account when purchasing new US equ
- EXCELLENT RESOURCES
- CLINICAL APPLICATIONS
- Slide 5
- Slide 6
- Slide 7
- What do you need to know to be professional in US
- Advantage of US OVER other modalities
- US development
- Slide 11
- What is Ultrasound machine
- Spectrum of sound
- Sound propagation
- Slide 15
- Wave propagation
- Difference between EM and sound
- How to produce sound wave
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Sound field
- Slide 26
- Transducer array
- Slide 28
- Ultrasound Display
- Real-time Scanning
- Linear Curved linear array Phased arraysector Endocavitary
- Transducer Arrays
- Electronic Scanning
- Electrical Scanning
- Linear Array Scanning
- Linear Switched Arrays
- Linear Switched Arrays (2)
- Linear Phased Array
- Linear Phased Array (2)
- Linear Phased Array (3)
- Linear Phased Array (4)
- Linear Phased Array (5)
- Linear Phased Array (6)
- Listening Mode
- 15 Transducer
- 15 amp 2D Transducers
- Remember me to explain why we use the backing block and matchin
- What we will use the returned or received ultrasound waves ldquoech
- Perpendicular Incidence
- Oblique Incidence
- Perpendicular Incidence (2)
- Perpendicular Incidence (3)
- Intensity Reflection Coefficient (IRC) amp Intensity Transmission
- IRC Equation
- Reflections
- Why Use Gel and matching layer
- Slide 57
- THE BASICS US IDEA
- What does your scanner know about echoed sound
- What Does Your Scanner Assume about Echoes (or how the scanner
- Distance of Echo from Transducer
- What is the Speed of Sound
- So the scanner assumes the wrong speed
- Attenuation Correction
- Gray Shade of Echo
- How does scanner know what gray shade to assign an echo
- How to reconstruct the image from echoes
- M Mode
- M-Mode (left ventricle)
- Scanner Processing of Echoes
- Amplification
- Compensation
- Need for Compensation
- Equal Echoes
- Compensation (TGC)
- Compensation (TGC) (2)
- Compression
- Compression (2)
- Demodulation
- Demodulation (2)
- Demodulation Sub-steps
- Rejection
- Rejection (2)
- Image Resolution
- Resolution amp Reflector Size
- Axial Resolution
- Axial Resolution (2)
- Axial Resolution (3)
- Spatial Pulse Length
- Wavelength
- Improve Axial Resolution by Reducing Spatial Pulse Length
- Slide 92
- Lateral Resolution
- Lateral Resolution (2)
- Lateral Resolution (3)
- Contrast Resolution
- Contrast Resolution (2)
- Pre-Processing
- Gray Scale
- Slide 100
- Display Limitations
- Presentation of Brightness Levels
- Slide 103
- Block Diagram
- B Mode
- Color flow imaging (mode) Color Doppler (mode)
- Continuous wave (CW) Doppler
- M-mode
- Power Doppler (mode)
- Pulsed wave Doppler
- Slide 111
- Slide 112
- Slide 113
- Slide 114
- DOPPLER US
- Hemodynamics
- Plug Flow
- Laminar Flow
- Flow
- Flow Pressure amp Resistance
- Doppler Shift
- Doppler Examples
- Doppler Angle
- Flow Components
- Doppler Sensing
- Doppler Sensing (2)
- Doppler Sensing (3)
- Doppler Equation
- Relationships
- Relationships (2)
- Doppler Relationships
- Continuous Wave Doppler
- Continuous Wave Doppler (2)
- Continuous Wave Doppler Receiver Function
- Pulse Wave vs Continuous Wave Doppler
- Dangers of Ultrasound
- Slide 137
- Slide 138
- Slide 139
- Ultrasound Terminology
- PZT is Most Common Piezoelectric Material
-
Dangers of Ultrasound
bullThere have been many concerns about the safety of ultrasound
ndashBecause ultrasound is energy the question becomes What is this energy doing to my tissues
or my baby
bullThere have been some reports of low birthweight babies being born to mothers who
had frequent ultrasound examinations during pregnancy
bullThe two major possibilities with ultrasound are as follows
ndashdevelopment of heat - tissues or water absorb the ultrasound energy which increases their
temperature locally ndashformation of bubbles (cavitation) - when dissolved
gases come out of solution due to local heat caused by ultrasound
bullHowever there have been no substantiated ill-effects of ultrasound documented in studies in
either humans or animals ndashThis being said ultrasound should still be used
only when necessary (ie better to be cautious)
Ultrasound Terminology
bull Impedance resistancebull steered
PZT is Most Common Piezoelectric Material
bullLead Zirconate TitanatebullAdvantages
ndashEfficientbullMore electrical energy transferred to sound amp vice-versa
ndashHigh natural resonance frequencyndashRepeatable characteristics
bullStable designbullDisadvantages
ndashHigh acoustic impedancebullCan cause poor acoustic couplingbullRequires matching layer to compensate
- UltarSound Machine Dr Fadhl Alakwaa
- What are the first things to account when purchasing new US equ
- EXCELLENT RESOURCES
- CLINICAL APPLICATIONS
- Slide 5
- Slide 6
- Slide 7
- What do you need to know to be professional in US
- Advantage of US OVER other modalities
- US development
- Slide 11
- What is Ultrasound machine
- Spectrum of sound
- Sound propagation
- Slide 15
- Wave propagation
- Difference between EM and sound
- How to produce sound wave
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Sound field
- Slide 26
- Transducer array
- Slide 28
- Ultrasound Display
- Real-time Scanning
- Linear Curved linear array Phased arraysector Endocavitary
- Transducer Arrays
- Electronic Scanning
- Electrical Scanning
- Linear Array Scanning
- Linear Switched Arrays
- Linear Switched Arrays (2)
- Linear Phased Array
- Linear Phased Array (2)
- Linear Phased Array (3)
- Linear Phased Array (4)
- Linear Phased Array (5)
- Linear Phased Array (6)
- Listening Mode
- 15 Transducer
- 15 amp 2D Transducers
- Remember me to explain why we use the backing block and matchin
- What we will use the returned or received ultrasound waves ldquoech
- Perpendicular Incidence
- Oblique Incidence
- Perpendicular Incidence (2)
- Perpendicular Incidence (3)
- Intensity Reflection Coefficient (IRC) amp Intensity Transmission
- IRC Equation
- Reflections
- Why Use Gel and matching layer
- Slide 57
- THE BASICS US IDEA
- What does your scanner know about echoed sound
- What Does Your Scanner Assume about Echoes (or how the scanner
- Distance of Echo from Transducer
- What is the Speed of Sound
- So the scanner assumes the wrong speed
- Attenuation Correction
- Gray Shade of Echo
- How does scanner know what gray shade to assign an echo
- How to reconstruct the image from echoes
- M Mode
- M-Mode (left ventricle)
- Scanner Processing of Echoes
- Amplification
- Compensation
- Need for Compensation
- Equal Echoes
- Compensation (TGC)
- Compensation (TGC) (2)
- Compression
- Compression (2)
- Demodulation
- Demodulation (2)
- Demodulation Sub-steps
- Rejection
- Rejection (2)
- Image Resolution
- Resolution amp Reflector Size
- Axial Resolution
- Axial Resolution (2)
- Axial Resolution (3)
- Spatial Pulse Length
- Wavelength
- Improve Axial Resolution by Reducing Spatial Pulse Length
- Slide 92
- Lateral Resolution
- Lateral Resolution (2)
- Lateral Resolution (3)
- Contrast Resolution
- Contrast Resolution (2)
- Pre-Processing
- Gray Scale
- Slide 100
- Display Limitations
- Presentation of Brightness Levels
- Slide 103
- Block Diagram
- B Mode
- Color flow imaging (mode) Color Doppler (mode)
- Continuous wave (CW) Doppler
- M-mode
- Power Doppler (mode)
- Pulsed wave Doppler
- Slide 111
- Slide 112
- Slide 113
- Slide 114
- DOPPLER US
- Hemodynamics
- Plug Flow
- Laminar Flow
- Flow
- Flow Pressure amp Resistance
- Doppler Shift
- Doppler Examples
- Doppler Angle
- Flow Components
- Doppler Sensing
- Doppler Sensing (2)
- Doppler Sensing (3)
- Doppler Equation
- Relationships
- Relationships (2)
- Doppler Relationships
- Continuous Wave Doppler
- Continuous Wave Doppler (2)
- Continuous Wave Doppler Receiver Function
- Pulse Wave vs Continuous Wave Doppler
- Dangers of Ultrasound
- Slide 137
- Slide 138
- Slide 139
- Ultrasound Terminology
- PZT is Most Common Piezoelectric Material
-
bullThere have been some reports of low birthweight babies being born to mothers who
had frequent ultrasound examinations during pregnancy
bullThe two major possibilities with ultrasound are as follows
ndashdevelopment of heat - tissues or water absorb the ultrasound energy which increases their
temperature locally ndashformation of bubbles (cavitation) - when dissolved
gases come out of solution due to local heat caused by ultrasound
bullHowever there have been no substantiated ill-effects of ultrasound documented in studies in
either humans or animals ndashThis being said ultrasound should still be used
only when necessary (ie better to be cautious)
Ultrasound Terminology
bull Impedance resistancebull steered
PZT is Most Common Piezoelectric Material
bullLead Zirconate TitanatebullAdvantages
ndashEfficientbullMore electrical energy transferred to sound amp vice-versa
ndashHigh natural resonance frequencyndashRepeatable characteristics
bullStable designbullDisadvantages
ndashHigh acoustic impedancebullCan cause poor acoustic couplingbullRequires matching layer to compensate
- UltarSound Machine Dr Fadhl Alakwaa
- What are the first things to account when purchasing new US equ
- EXCELLENT RESOURCES
- CLINICAL APPLICATIONS
- Slide 5
- Slide 6
- Slide 7
- What do you need to know to be professional in US
- Advantage of US OVER other modalities
- US development
- Slide 11
- What is Ultrasound machine
- Spectrum of sound
- Sound propagation
- Slide 15
- Wave propagation
- Difference between EM and sound
- How to produce sound wave
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Sound field
- Slide 26
- Transducer array
- Slide 28
- Ultrasound Display
- Real-time Scanning
- Linear Curved linear array Phased arraysector Endocavitary
- Transducer Arrays
- Electronic Scanning
- Electrical Scanning
- Linear Array Scanning
- Linear Switched Arrays
- Linear Switched Arrays (2)
- Linear Phased Array
- Linear Phased Array (2)
- Linear Phased Array (3)
- Linear Phased Array (4)
- Linear Phased Array (5)
- Linear Phased Array (6)
- Listening Mode
- 15 Transducer
- 15 amp 2D Transducers
- Remember me to explain why we use the backing block and matchin
- What we will use the returned or received ultrasound waves ldquoech
- Perpendicular Incidence
- Oblique Incidence
- Perpendicular Incidence (2)
- Perpendicular Incidence (3)
- Intensity Reflection Coefficient (IRC) amp Intensity Transmission
- IRC Equation
- Reflections
- Why Use Gel and matching layer
- Slide 57
- THE BASICS US IDEA
- What does your scanner know about echoed sound
- What Does Your Scanner Assume about Echoes (or how the scanner
- Distance of Echo from Transducer
- What is the Speed of Sound
- So the scanner assumes the wrong speed
- Attenuation Correction
- Gray Shade of Echo
- How does scanner know what gray shade to assign an echo
- How to reconstruct the image from echoes
- M Mode
- M-Mode (left ventricle)
- Scanner Processing of Echoes
- Amplification
- Compensation
- Need for Compensation
- Equal Echoes
- Compensation (TGC)
- Compensation (TGC) (2)
- Compression
- Compression (2)
- Demodulation
- Demodulation (2)
- Demodulation Sub-steps
- Rejection
- Rejection (2)
- Image Resolution
- Resolution amp Reflector Size
- Axial Resolution
- Axial Resolution (2)
- Axial Resolution (3)
- Spatial Pulse Length
- Wavelength
- Improve Axial Resolution by Reducing Spatial Pulse Length
- Slide 92
- Lateral Resolution
- Lateral Resolution (2)
- Lateral Resolution (3)
- Contrast Resolution
- Contrast Resolution (2)
- Pre-Processing
- Gray Scale
- Slide 100
- Display Limitations
- Presentation of Brightness Levels
- Slide 103
- Block Diagram
- B Mode
- Color flow imaging (mode) Color Doppler (mode)
- Continuous wave (CW) Doppler
- M-mode
- Power Doppler (mode)
- Pulsed wave Doppler
- Slide 111
- Slide 112
- Slide 113
- Slide 114
- DOPPLER US
- Hemodynamics
- Plug Flow
- Laminar Flow
- Flow
- Flow Pressure amp Resistance
- Doppler Shift
- Doppler Examples
- Doppler Angle
- Flow Components
- Doppler Sensing
- Doppler Sensing (2)
- Doppler Sensing (3)
- Doppler Equation
- Relationships
- Relationships (2)
- Doppler Relationships
- Continuous Wave Doppler
- Continuous Wave Doppler (2)
- Continuous Wave Doppler Receiver Function
- Pulse Wave vs Continuous Wave Doppler
- Dangers of Ultrasound
- Slide 137
- Slide 138
- Slide 139
- Ultrasound Terminology
- PZT is Most Common Piezoelectric Material
-
bullThe two major possibilities with ultrasound are as follows
ndashdevelopment of heat - tissues or water absorb the ultrasound energy which increases their
temperature locally ndashformation of bubbles (cavitation) - when dissolved
gases come out of solution due to local heat caused by ultrasound
bullHowever there have been no substantiated ill-effects of ultrasound documented in studies in
either humans or animals ndashThis being said ultrasound should still be used
only when necessary (ie better to be cautious)
Ultrasound Terminology
bull Impedance resistancebull steered
PZT is Most Common Piezoelectric Material
bullLead Zirconate TitanatebullAdvantages
ndashEfficientbullMore electrical energy transferred to sound amp vice-versa
ndashHigh natural resonance frequencyndashRepeatable characteristics
bullStable designbullDisadvantages
ndashHigh acoustic impedancebullCan cause poor acoustic couplingbullRequires matching layer to compensate
- UltarSound Machine Dr Fadhl Alakwaa
- What are the first things to account when purchasing new US equ
- EXCELLENT RESOURCES
- CLINICAL APPLICATIONS
- Slide 5
- Slide 6
- Slide 7
- What do you need to know to be professional in US
- Advantage of US OVER other modalities
- US development
- Slide 11
- What is Ultrasound machine
- Spectrum of sound
- Sound propagation
- Slide 15
- Wave propagation
- Difference between EM and sound
- How to produce sound wave
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Sound field
- Slide 26
- Transducer array
- Slide 28
- Ultrasound Display
- Real-time Scanning
- Linear Curved linear array Phased arraysector Endocavitary
- Transducer Arrays
- Electronic Scanning
- Electrical Scanning
- Linear Array Scanning
- Linear Switched Arrays
- Linear Switched Arrays (2)
- Linear Phased Array
- Linear Phased Array (2)
- Linear Phased Array (3)
- Linear Phased Array (4)
- Linear Phased Array (5)
- Linear Phased Array (6)
- Listening Mode
- 15 Transducer
- 15 amp 2D Transducers
- Remember me to explain why we use the backing block and matchin
- What we will use the returned or received ultrasound waves ldquoech
- Perpendicular Incidence
- Oblique Incidence
- Perpendicular Incidence (2)
- Perpendicular Incidence (3)
- Intensity Reflection Coefficient (IRC) amp Intensity Transmission
- IRC Equation
- Reflections
- Why Use Gel and matching layer
- Slide 57
- THE BASICS US IDEA
- What does your scanner know about echoed sound
- What Does Your Scanner Assume about Echoes (or how the scanner
- Distance of Echo from Transducer
- What is the Speed of Sound
- So the scanner assumes the wrong speed
- Attenuation Correction
- Gray Shade of Echo
- How does scanner know what gray shade to assign an echo
- How to reconstruct the image from echoes
- M Mode
- M-Mode (left ventricle)
- Scanner Processing of Echoes
- Amplification
- Compensation
- Need for Compensation
- Equal Echoes
- Compensation (TGC)
- Compensation (TGC) (2)
- Compression
- Compression (2)
- Demodulation
- Demodulation (2)
- Demodulation Sub-steps
- Rejection
- Rejection (2)
- Image Resolution
- Resolution amp Reflector Size
- Axial Resolution
- Axial Resolution (2)
- Axial Resolution (3)
- Spatial Pulse Length
- Wavelength
- Improve Axial Resolution by Reducing Spatial Pulse Length
- Slide 92
- Lateral Resolution
- Lateral Resolution (2)
- Lateral Resolution (3)
- Contrast Resolution
- Contrast Resolution (2)
- Pre-Processing
- Gray Scale
- Slide 100
- Display Limitations
- Presentation of Brightness Levels
- Slide 103
- Block Diagram
- B Mode
- Color flow imaging (mode) Color Doppler (mode)
- Continuous wave (CW) Doppler
- M-mode
- Power Doppler (mode)
- Pulsed wave Doppler
- Slide 111
- Slide 112
- Slide 113
- Slide 114
- DOPPLER US
- Hemodynamics
- Plug Flow
- Laminar Flow
- Flow
- Flow Pressure amp Resistance
- Doppler Shift
- Doppler Examples
- Doppler Angle
- Flow Components
- Doppler Sensing
- Doppler Sensing (2)
- Doppler Sensing (3)
- Doppler Equation
- Relationships
- Relationships (2)
- Doppler Relationships
- Continuous Wave Doppler
- Continuous Wave Doppler (2)
- Continuous Wave Doppler Receiver Function
- Pulse Wave vs Continuous Wave Doppler
- Dangers of Ultrasound
- Slide 137
- Slide 138
- Slide 139
- Ultrasound Terminology
- PZT is Most Common Piezoelectric Material
-
bullHowever there have been no substantiated ill-effects of ultrasound documented in studies in
either humans or animals ndashThis being said ultrasound should still be used
only when necessary (ie better to be cautious)
Ultrasound Terminology
bull Impedance resistancebull steered
PZT is Most Common Piezoelectric Material
bullLead Zirconate TitanatebullAdvantages
ndashEfficientbullMore electrical energy transferred to sound amp vice-versa
ndashHigh natural resonance frequencyndashRepeatable characteristics
bullStable designbullDisadvantages
ndashHigh acoustic impedancebullCan cause poor acoustic couplingbullRequires matching layer to compensate
- UltarSound Machine Dr Fadhl Alakwaa
- What are the first things to account when purchasing new US equ
- EXCELLENT RESOURCES
- CLINICAL APPLICATIONS
- Slide 5
- Slide 6
- Slide 7
- What do you need to know to be professional in US
- Advantage of US OVER other modalities
- US development
- Slide 11
- What is Ultrasound machine
- Spectrum of sound
- Sound propagation
- Slide 15
- Wave propagation
- Difference between EM and sound
- How to produce sound wave
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Sound field
- Slide 26
- Transducer array
- Slide 28
- Ultrasound Display
- Real-time Scanning
- Linear Curved linear array Phased arraysector Endocavitary
- Transducer Arrays
- Electronic Scanning
- Electrical Scanning
- Linear Array Scanning
- Linear Switched Arrays
- Linear Switched Arrays (2)
- Linear Phased Array
- Linear Phased Array (2)
- Linear Phased Array (3)
- Linear Phased Array (4)
- Linear Phased Array (5)
- Linear Phased Array (6)
- Listening Mode
- 15 Transducer
- 15 amp 2D Transducers
- Remember me to explain why we use the backing block and matchin
- What we will use the returned or received ultrasound waves ldquoech
- Perpendicular Incidence
- Oblique Incidence
- Perpendicular Incidence (2)
- Perpendicular Incidence (3)
- Intensity Reflection Coefficient (IRC) amp Intensity Transmission
- IRC Equation
- Reflections
- Why Use Gel and matching layer
- Slide 57
- THE BASICS US IDEA
- What does your scanner know about echoed sound
- What Does Your Scanner Assume about Echoes (or how the scanner
- Distance of Echo from Transducer
- What is the Speed of Sound
- So the scanner assumes the wrong speed
- Attenuation Correction
- Gray Shade of Echo
- How does scanner know what gray shade to assign an echo
- How to reconstruct the image from echoes
- M Mode
- M-Mode (left ventricle)
- Scanner Processing of Echoes
- Amplification
- Compensation
- Need for Compensation
- Equal Echoes
- Compensation (TGC)
- Compensation (TGC) (2)
- Compression
- Compression (2)
- Demodulation
- Demodulation (2)
- Demodulation Sub-steps
- Rejection
- Rejection (2)
- Image Resolution
- Resolution amp Reflector Size
- Axial Resolution
- Axial Resolution (2)
- Axial Resolution (3)
- Spatial Pulse Length
- Wavelength
- Improve Axial Resolution by Reducing Spatial Pulse Length
- Slide 92
- Lateral Resolution
- Lateral Resolution (2)
- Lateral Resolution (3)
- Contrast Resolution
- Contrast Resolution (2)
- Pre-Processing
- Gray Scale
- Slide 100
- Display Limitations
- Presentation of Brightness Levels
- Slide 103
- Block Diagram
- B Mode
- Color flow imaging (mode) Color Doppler (mode)
- Continuous wave (CW) Doppler
- M-mode
- Power Doppler (mode)
- Pulsed wave Doppler
- Slide 111
- Slide 112
- Slide 113
- Slide 114
- DOPPLER US
- Hemodynamics
- Plug Flow
- Laminar Flow
- Flow
- Flow Pressure amp Resistance
- Doppler Shift
- Doppler Examples
- Doppler Angle
- Flow Components
- Doppler Sensing
- Doppler Sensing (2)
- Doppler Sensing (3)
- Doppler Equation
- Relationships
- Relationships (2)
- Doppler Relationships
- Continuous Wave Doppler
- Continuous Wave Doppler (2)
- Continuous Wave Doppler Receiver Function
- Pulse Wave vs Continuous Wave Doppler
- Dangers of Ultrasound
- Slide 137
- Slide 138
- Slide 139
- Ultrasound Terminology
- PZT is Most Common Piezoelectric Material
-
Ultrasound Terminology
bull Impedance resistancebull steered
PZT is Most Common Piezoelectric Material
bullLead Zirconate TitanatebullAdvantages
ndashEfficientbullMore electrical energy transferred to sound amp vice-versa
ndashHigh natural resonance frequencyndashRepeatable characteristics
bullStable designbullDisadvantages
ndashHigh acoustic impedancebullCan cause poor acoustic couplingbullRequires matching layer to compensate
- UltarSound Machine Dr Fadhl Alakwaa
- What are the first things to account when purchasing new US equ
- EXCELLENT RESOURCES
- CLINICAL APPLICATIONS
- Slide 5
- Slide 6
- Slide 7
- What do you need to know to be professional in US
- Advantage of US OVER other modalities
- US development
- Slide 11
- What is Ultrasound machine
- Spectrum of sound
- Sound propagation
- Slide 15
- Wave propagation
- Difference between EM and sound
- How to produce sound wave
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Sound field
- Slide 26
- Transducer array
- Slide 28
- Ultrasound Display
- Real-time Scanning
- Linear Curved linear array Phased arraysector Endocavitary
- Transducer Arrays
- Electronic Scanning
- Electrical Scanning
- Linear Array Scanning
- Linear Switched Arrays
- Linear Switched Arrays (2)
- Linear Phased Array
- Linear Phased Array (2)
- Linear Phased Array (3)
- Linear Phased Array (4)
- Linear Phased Array (5)
- Linear Phased Array (6)
- Listening Mode
- 15 Transducer
- 15 amp 2D Transducers
- Remember me to explain why we use the backing block and matchin
- What we will use the returned or received ultrasound waves ldquoech
- Perpendicular Incidence
- Oblique Incidence
- Perpendicular Incidence (2)
- Perpendicular Incidence (3)
- Intensity Reflection Coefficient (IRC) amp Intensity Transmission
- IRC Equation
- Reflections
- Why Use Gel and matching layer
- Slide 57
- THE BASICS US IDEA
- What does your scanner know about echoed sound
- What Does Your Scanner Assume about Echoes (or how the scanner
- Distance of Echo from Transducer
- What is the Speed of Sound
- So the scanner assumes the wrong speed
- Attenuation Correction
- Gray Shade of Echo
- How does scanner know what gray shade to assign an echo
- How to reconstruct the image from echoes
- M Mode
- M-Mode (left ventricle)
- Scanner Processing of Echoes
- Amplification
- Compensation
- Need for Compensation
- Equal Echoes
- Compensation (TGC)
- Compensation (TGC) (2)
- Compression
- Compression (2)
- Demodulation
- Demodulation (2)
- Demodulation Sub-steps
- Rejection
- Rejection (2)
- Image Resolution
- Resolution amp Reflector Size
- Axial Resolution
- Axial Resolution (2)
- Axial Resolution (3)
- Spatial Pulse Length
- Wavelength
- Improve Axial Resolution by Reducing Spatial Pulse Length
- Slide 92
- Lateral Resolution
- Lateral Resolution (2)
- Lateral Resolution (3)
- Contrast Resolution
- Contrast Resolution (2)
- Pre-Processing
- Gray Scale
- Slide 100
- Display Limitations
- Presentation of Brightness Levels
- Slide 103
- Block Diagram
- B Mode
- Color flow imaging (mode) Color Doppler (mode)
- Continuous wave (CW) Doppler
- M-mode
- Power Doppler (mode)
- Pulsed wave Doppler
- Slide 111
- Slide 112
- Slide 113
- Slide 114
- DOPPLER US
- Hemodynamics
- Plug Flow
- Laminar Flow
- Flow
- Flow Pressure amp Resistance
- Doppler Shift
- Doppler Examples
- Doppler Angle
- Flow Components
- Doppler Sensing
- Doppler Sensing (2)
- Doppler Sensing (3)
- Doppler Equation
- Relationships
- Relationships (2)
- Doppler Relationships
- Continuous Wave Doppler
- Continuous Wave Doppler (2)
- Continuous Wave Doppler Receiver Function
- Pulse Wave vs Continuous Wave Doppler
- Dangers of Ultrasound
- Slide 137
- Slide 138
- Slide 139
- Ultrasound Terminology
- PZT is Most Common Piezoelectric Material
-
PZT is Most Common Piezoelectric Material
bullLead Zirconate TitanatebullAdvantages
ndashEfficientbullMore electrical energy transferred to sound amp vice-versa
ndashHigh natural resonance frequencyndashRepeatable characteristics
bullStable designbullDisadvantages
ndashHigh acoustic impedancebullCan cause poor acoustic couplingbullRequires matching layer to compensate
- UltarSound Machine Dr Fadhl Alakwaa
- What are the first things to account when purchasing new US equ
- EXCELLENT RESOURCES
- CLINICAL APPLICATIONS
- Slide 5
- Slide 6
- Slide 7
- What do you need to know to be professional in US
- Advantage of US OVER other modalities
- US development
- Slide 11
- What is Ultrasound machine
- Spectrum of sound
- Sound propagation
- Slide 15
- Wave propagation
- Difference between EM and sound
- How to produce sound wave
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Sound field
- Slide 26
- Transducer array
- Slide 28
- Ultrasound Display
- Real-time Scanning
- Linear Curved linear array Phased arraysector Endocavitary
- Transducer Arrays
- Electronic Scanning
- Electrical Scanning
- Linear Array Scanning
- Linear Switched Arrays
- Linear Switched Arrays (2)
- Linear Phased Array
- Linear Phased Array (2)
- Linear Phased Array (3)
- Linear Phased Array (4)
- Linear Phased Array (5)
- Linear Phased Array (6)
- Listening Mode
- 15 Transducer
- 15 amp 2D Transducers
- Remember me to explain why we use the backing block and matchin
- What we will use the returned or received ultrasound waves ldquoech
- Perpendicular Incidence
- Oblique Incidence
- Perpendicular Incidence (2)
- Perpendicular Incidence (3)
- Intensity Reflection Coefficient (IRC) amp Intensity Transmission
- IRC Equation
- Reflections
- Why Use Gel and matching layer
- Slide 57
- THE BASICS US IDEA
- What does your scanner know about echoed sound
- What Does Your Scanner Assume about Echoes (or how the scanner
- Distance of Echo from Transducer
- What is the Speed of Sound
- So the scanner assumes the wrong speed
- Attenuation Correction
- Gray Shade of Echo
- How does scanner know what gray shade to assign an echo
- How to reconstruct the image from echoes
- M Mode
- M-Mode (left ventricle)
- Scanner Processing of Echoes
- Amplification
- Compensation
- Need for Compensation
- Equal Echoes
- Compensation (TGC)
- Compensation (TGC) (2)
- Compression
- Compression (2)
- Demodulation
- Demodulation (2)
- Demodulation Sub-steps
- Rejection
- Rejection (2)
- Image Resolution
- Resolution amp Reflector Size
- Axial Resolution
- Axial Resolution (2)
- Axial Resolution (3)
- Spatial Pulse Length
- Wavelength
- Improve Axial Resolution by Reducing Spatial Pulse Length
- Slide 92
- Lateral Resolution
- Lateral Resolution (2)
- Lateral Resolution (3)
- Contrast Resolution
- Contrast Resolution (2)
- Pre-Processing
- Gray Scale
- Slide 100
- Display Limitations
- Presentation of Brightness Levels
- Slide 103
- Block Diagram
- B Mode
- Color flow imaging (mode) Color Doppler (mode)
- Continuous wave (CW) Doppler
- M-mode
- Power Doppler (mode)
- Pulsed wave Doppler
- Slide 111
- Slide 112
- Slide 113
- Slide 114
- DOPPLER US
- Hemodynamics
- Plug Flow
- Laminar Flow
- Flow
- Flow Pressure amp Resistance
- Doppler Shift
- Doppler Examples
- Doppler Angle
- Flow Components
- Doppler Sensing
- Doppler Sensing (2)
- Doppler Sensing (3)
- Doppler Equation
- Relationships
- Relationships (2)
- Doppler Relationships
- Continuous Wave Doppler
- Continuous Wave Doppler (2)
- Continuous Wave Doppler Receiver Function
- Pulse Wave vs Continuous Wave Doppler
- Dangers of Ultrasound
- Slide 137
- Slide 138
- Slide 139
- Ultrasound Terminology
- PZT is Most Common Piezoelectric Material
-