Medical Ultrasound Imaggging€¦ · Ultrasound instruments 3. Main principles 4. Imaging modes 5....
Transcript of Medical Ultrasound Imaggging€¦ · Ultrasound instruments 3. Main principles 4. Imaging modes 5....
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Medical Ultrasound Imagingg g
Sverre HolmDigital Signal Processing and
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Image Analysis Group
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Medical UltrasoundMedical Ultrasound1. Introduction2. Ultrasound instruments3. Main principles4 Imaging modes4. Imaging modes5. Probe types and image
formats6. Bioeffects and safety7. Emerging technology
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Medical Ultrasound usesMedical Ultrasound uses• Soft tissues
– Fetal, liver, kidneys
• Dynamics of blood flowH t i l t t– Heart, circulatory system
• Avoid bone, and air (lungs)
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Liver: A scan which was considered to be of high quality in the early 1970s and whichLiver: A scan which was considered to be of high quality in the early 1970s and which would have been interpreted as supporting the diagnosis of multiple metastases.Wells, Ultrasound imaging, 2006
Metastasis = the spread of a disease from one organ or part to another non-adjacent organ or part.
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Metastasis the spread of a disease from one organ or part to another non adjacent organ or part. Concerned mainly with malignant tumor cells and infections (Wikipedia)
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Liver: A scan made with a modern system, in which a metastasis can just be perceived towards the right side of the patient (i.e., towards the left of the image)
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Wells, Ultrasound imaging, 2006
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Liver, metastasis: a scan of the same patient, in which this lesion is clearly apparent following the administration of an ultrasonic contrast agent.
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Wells, Ultrasound imaging, 2006
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Medical UltrasoundMedical Ultrasound• Continuously improving image quality =>
i d li i lincreased clinical usage• Relatively inexpensive compared to CT and MR
25% f ll i i i h it l i US– 25% of all imaging exams in hospitals is US
• Many clinical applications• Requires training and skill• Requires training and skill
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Norway: 30-40 years of developmentNorway: 30 40 years of development• 70’s: Started at NTNU, continued R&D since then
– L. Hatle og B. A. J. Angelsen, Doppler Ultrasound in Cardiology, Lea & Feibiger, Phil d l hi 1985
g g pp gy gPhiladelphia, 1985.
– B. A. J. Angelsen, Waves, Signals, and Signal Processing in Medical Ultrasonics, Vol I & Vol II, Institutt for fysiologi og biomedisinsk teknikk, NTNU, april 1996 +
– 2006-2014: Medical Imaging, Centre for Research-based Innovation g g,http://www.ntnu.no/milab
• 80’s: Vingmed Sound• 1998: GE Vingmed Ultrasound,
Now center of excellence for cardiology ultrasound in GE Healthcare– Now center of excellence for cardiology ultrasound in GE Healthcare – More than 2 billion NOK turnover controlled from Horten, Norway
• Other companies: – Medistim (quality control in surgery) on Oslo Stock Exchange
S d (i id d b d f i f lt d d MR)– Sonowand (image-guided surgery based on fusion of ultrasound and MR) – Neorad (ultrasound-guided injection of CT contrast agent in vein)– Auratech (High quality ultrasound engines/electronics)
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Medical UltrasoundMedical Ultrasound1. Introduction2. Ultrasound instruments3. Main principles4 Imaging modes4. Imaging modes5. Probe types and image
formats6. Bioeffects and safety7. Emerging technology
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Medical Ultrasound MarketsMedical Ultrasound Markets• Cardiology (Heart) 25% of market
– Field where Norwegian company Vingmed was established in the 80’s as a startup from NTNU Now GE Vingmed Ultrasound center of excellence for cardiology ultrasound in GENTNU. Now GE Vingmed Ultrasound, center of excellence for cardiology ultrasound in GE Healthcare
– Demo later in course• Radiology (Inner organs) 40%• Obstetrics/Gynecology 20%y gy• Niches
– Vascular– Urology (B&K Medical, Denmark)– Surgery (Medistim AS and Sonowand AS)– Emergency medicine (driver for handheld ultrasound)– General practice– Dermatology (skin)– Veterinary– Small animals for medical experiments/testingp g– ...
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High-end Ultrasound providersHigh end Ultrasound providers• Philips
– Acquired ATL ,Seattle WA, and HP/Agilent, Boston MA
• SiemensA i d A Sili V ll– Acquired Acuson, Silicon Valley
• GE Healthcare– Acquired VingmedAcquired Vingmed
• Japan: Toshiba, Hitachi, Aloka• Emerging? France: Supersonic ImagineEmerging? France: Supersonic Imagine
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www geultrasound comwww.geultrasound.com
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Laptop ultrasound Sonosite M TurboLaptop ultrasoundGE Logiq Book XP
Sonosite M-Turbo
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Pocket Ultrasound: GE VScanPocket Ultrasound: GE VScan• Developed by GE Vingmed
Ult d i NUltrasound in Norway– For cardiologists or primary care– Liver, gall bladder, kidney, fetalLiver, gall bladder, kidney, fetal
position, cardiac, aorta
• No 14, Time Magazine’s list The 50 Best Inventions ofThe 50 Best Inventions of 2009
• Winner Årets ingeniørbragdWinner Årets ingeniørbragd, Norway 2009
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Medical UltrasoundMedical Ultrasound1. Introduction2. Ultrasound instruments3. Main principles4 Imaging modes4. Imaging modes5. Probe types and image
formats6. Bioeffects and safety7. Emerging technology
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Longitudinal/Compression WavesLongitudinal/Compression Waves
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Sook Kien Ng, Ultrasound Imaging
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Ultrasound: Interaction with tissueUltrasound: Interaction with tissueMajor interaction mechanisms:
1. Scattering (Imaging + Doppler)
f ( )2. Reflection (Imaging)3. Refraction4. Attenuatione ua o
Lawrence Physics and instrumentation ofLawrence, Physics and instrumentation of ultrasound, 2007.
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1 Scattering1. ScatteringA) Rough interfaces
B) Inhomogenous medium (causing speckle in images)
C) Particles (red blood cells)
Burns, Introduction to the physical principles of ultrasound imaging and d l 2005doppler, 2005
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2 Reflection 3 Refraction2. Reflection, 3. Refraction• Due to changes in acoustic
impedance Z=·cp • Specular
– Like light striking a glass plate –Snell’s law
E h ill l b i d if• Echoes will only be received if beam is near perpendicular
– Wall of an organ: heart, bladder
• Refraction in some cases –• Refraction in some cases –rare anomalies
Burns, Introduction to the physical principles of ultrasound imaging and d l 2005
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doppler, 2005
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Reflection coefficientReflection coefficient• At any interface between two materials:
Reflection coefficient:• Reflection coefficient:– r = amplitude of reflected/amplitude of incident wave– -1 ≤ r ≤ 1
• Reflection coefficient given by:– : density, c: speed of sound,– c = (/ρ)0.5 where is bulk compression modulus( ρ) p– Z = c = (ρ)0.5 : acoustic impedance, Rayleigh (Rayl)
221121 ccZZZZr
221121 ccZZ
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Reflection coefficientMedium Density Speed of
soundImpedance r
Air -> 1.3 kg/m3 340 m/s 442 Raylg ysteel 7800 kg/m3 5800 m/s 45.24 MRayl -0.99998
(1800 phase shift)
water 1000 kg/m3 1490 m/s 1.49 Mrayl -0.981water 1000 kg/m 1490 m/s 1.49 Mrayl 0.981
Water -> 1.49 MRayl
steel 45 24 MRayl -0 936steel 45.24 MRayl 0.936Muscle tissue -> 1100 kg/m3 1540 m/s 1.7 MRayl
water 1.49 MRayl 0.07ylungs = air 442 Rayl 0.9995
bone 4080 m/s 3.8 ... -0.38 ...
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7.4 MRayl -0.63This is why ultrasound imaging works
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4 Attenuation4. Attenuation• In water: usually increases with f2
1• In tissue: usually increases with f1
• Typically = 0.5-1 dB/cm/MHz• Attenuation = 2d··f1
• Examples 80 dB attenuation ( = 0.5 dB/cm/MHz):– f = 1 MHz: d=80 cm depth, = 1.5 mm => 533 depth– f = 3 MHz: d=26 7 cm depth = 0 5 mm => 533 depthf = 3 MHz: d=26.7 cm depth, = 0.5 mm => 533 depth– f = 10 MHz: d=8 cm depth, = 0.15 mm => 533 depth
• Pavlin, Foster, Ultrasound Microscopy 1998
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4. Attenuation Center frequency shifts with depthCenter frequency shifts with depth
Can show that for a Gaussian spectrum, the center frequency will fall linearly with depth for f1attenuation (Kuc
5 cm
10 cmattenuation (Kuc, 1984, IEEE ASSP)
Simulated in Ultrasim for depths
15 cm
20 cmfor depths 5,10,15,20 cm
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4 Attenuation: Max depth of an image4. Attenuation: Max depth of an image• Depth where attenuation reaches ~60 dB
– Attenuation = 2d··f => d = Attenuation/(2··f)
• Examples: 60 dB attenuation ( = 0 5 dB/cm/MHz):Examples: 60 dB attenuation ( 0.5 dB/cm/MHz):– f = 2.6 MHz: d = 23.1 cm depth– f = 3 MHz: d = 20 cm depth
f = 5 MHz: d = 12 cm depth– f = 5 MHz: d = 12 cm depth– f = 10 MHz: d = 6 cm depth
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4. Attenuation: PRF Pulse Repetion FrequencyPRF - Pulse Repetion Frequency• d = Attenuation/(2··f), where = 0.5 dB/cm/MHz• Max depth, example: d=23.1 cm, c=1540 m/s• Time to travel up and down: T = 2d/c = 0.3 ms• Pulse Repetition Frequency PRF = 1/T = 3333 Hz• PRF = Framerate for A- and M-modes• Too high PRF => Spatial ”aliasing”:
Tx pulse 1 23.1 cm Strong echo @ 25 cm
Tx pulse 2
Time/2-way range, pulse 1
Time/2-way range, pulse 2
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Modeling of ultrasound propagationModeling of ultrasound propagation• Lossless wave equation, u is displacement (or pressure):
1 ∂2u
• Standard viscous wave equation – attenuation prop. to ω2
∇2u− 1
c20
∂2u
∂t2= 0
• Fractional wave eq (Holm Sinkus Journ Acoust Soc Am Jan
∇2u− 1
c20
∂2u
∂t2+ τ
∂
∂t(∇2u) = 0
• Fractional wave eq. (Holm, Sinkus Journ. Acoust. Soc. Am, Jan 2010 + Holm, Näsholm. Journ. Acoust. Soc. Am, Oct. 2011.) –attenuation prop. to ωα+1 as in medical ultrasound
∇2 1 ∂2u+ α ∂α
(∇2 ) 0
• Derivatives of order α – not an integer - fractional derivatives: http://blogg.uio.no/mn/ifi/innovasjonsteknologi/content/bedre-diagnose-ved-bedre-derivasjon
∇2u−c20 ∂t2
+ τα∂tα
(∇2u) = 0
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http://blogg.uio.no/mn/ifi/innovasjonsteknologi/content/bedre diagnose ved bedre derivasjon
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Resolution vs penetrationResolution vs penetration• Radial and lateral
resolution improve withresolution improve with frequency
• Penetration falls with ffrequency
• Results in a near optimum frequency for an organ of a given size and depth:
– 2.5 – 3.5 MHz cardiology– 5 – 7.5 MHz cardiology5 7.5 MHz cardiology
children; peripheral vessels
– 3.5 – 5 MHz fetal imaging
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g g• Pavlin, Foster, Ultrasound Microscopy 1998
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1D probe for 2D imaging• 32-128 elements
B f i i th i th
1D probe for 2D imaging
• Beamforming in the azimuth plane for steering and control of the beam
• Acoustic lens for focusing in• Acoustic lens for focusing in the elevation dimension
• Azimuth = in-plane = x• Elevation = out-of-plane = y
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ResolutionResolutionTwo dimensions:1. Radial or depth resolution2. Azimuth or lateral
resolution – orthogonal to gbeam direction. • Usually hardest to improve,
as illustrated
Objekt Bilde
Object Image
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Ill.: B. Angelsen, NTNU
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Radial resolution (as in sonar )Radial resolution (as in sonar ...)• Resolution = half the pulse
length
S ll l d l ti
)2/(2/ Bccr • Small value = good resolution
= the ability to resolve two neighboring objects
• Also inverse proportional to band idthbandwidth
• As bandwidth usually is a fraction of the center frequency, resolution is inverse proportional to centreinverse proportional to centre frequency, e.g. B=50% of f0
• Example f0 = 3.5 MHz, B = 0.5 3.5 MHz => r = 1500 / (2*1 75e6) 0 43 mm
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(2*1.75e6) 0.43 mm
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Pulse compression in ultrasound?Pulse compression in ultrasound?NO YES• Blind zone equal to
the pulse length• Pulse Inversion in
nonlinear acousticsp g• Depth-dependent
filtering due to gfrequency dependent attenuation
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Lateral resolutionLateral resolution• Angular resolution for a source of size D:
• At a distance F (small angles approx.):
• Res best near the source (small F)Res. best near the source (small F)• Res. increases with frequency, f0• Ex: f0=3.5 MHz, =c/f0= 1500/3.5e6
0 43 mm0.43 mm• Cardiology: D=19 mm, F=0.43/19 =
0.023 rad = 1.3o. At depth 10 cm D =0 023*100 = 2 3 mmDF=0.023 100 = 2.3 mm
• Abdominal: D=40 mm => F=0.62o
• Radial res. usually much better than lateral res D = 2 3 mm >> r = 0 43 mm
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lateral res. DF= 2.3 mm >> r = 0.43 mm
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Th G t W ff K K t hik H k i (1760 1849)INSTITUTT FOR INFORMATIKK SH, 33
The Great Wave off Kanagawa. Katsushika Hokusai (1760–1849)
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Nonlinear pulse shape measured in t t k i l bwater tank in our lab
Fabrice Prieur, Sept. 2009
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Non-linear acousticsNon linear acousticsThe velocity of sound, c, varies with the amplitude, s:
• A and B are the 1.and 2. order Taylor series coefficients for the pressure. B/A is a measure of the non-linearity.
• s(t) = pressure = p0 + p1(t)– p0 = 1 atmosphere– p1(t) = applied pressure variation (= ”signal”)1
• Two sources of nonlinearity:– Inherent in the material’s properties (equation of state): B/2A– Due to convection: the ’1’ exists even if material nonlinearity B/2A = 0
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Due to convection: the 1 , exists even if material nonlinearity, B/2A = 0
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Non-linear acousticsNon linear acoustics• Positive peaks propagate faster than negative
kpeaks:– Waveform is distorted.– More and more energy is transferred to higher harmonics asMore and more energy is transferred to higher harmonics as
the wave propagates.– Eventually a shock wave is formed.
B/A:• B/A:– Linear medium: B/A = 0– Salt water: B/A=5.2, ,– Blood and tissue: B/A=6,..., 10.
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Non-linear acousticsNon linear acoustics
Whittingham, 2007
P i i ff i• Positive effect on images:– 2. harmonic beam is narrower => better resolution– Is not generated in sidelobes of 1. harmonic beam => less sidelobes– Is generated inside medium => avoids some of the aberrations andIs generated inside medium > avoids some of the aberrations and
reverberations from chest wall• Negative effect:
– 2. harmonic attenuates faster => less penetration
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LiverLiver• Harmonic
imaging• Octave
imaging
INSTITUTT FOR INFORMATIKK SH, 38Fundamental 2. harmonic
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Nonlinear acoustics wave equationsNonlinear acoustics, wave equations
∇2p− 1 ∂2p+
δ ∂3p= − β ∂2p2
• Westervelt equation: p is pressure, c0 is speed of d i d it δ i l f t β 1 B/A i
∇ pc20 ∂t
2p+
c40 ∂t3=
ρ0c40 ∂t2
sound, ρ0 is density, δ is loss factor, β =1+B/A is nonlinearity coefficient
• Viscous loss attenuation prop to ω2 good for• Viscous loss, attenuation prop to ω2, good for water and air, not so good for medical ultrasound
• Prieur Holm ”Nonlinear acoustics with fractionalPrieur, Holm, Nonlinear acoustics with fractional loss operators,” Journ Acoust Soc Am, 2011, 2012 - other powers than 2
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Medical UltrasoundMedical Ultrasound1. Introduction2. Ultrasound instruments3. Main principles4 Imaging modes4. Imaging modes5. Probe types and image
formats6. Bioeffects and safety7. Emerging technology
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Medical Ultrasound ScannerMedical Ultrasound Scanner• Imaging modes:
– A-mode (A = amplitude)– M-mode (M = motion)– B-mode 2D (B = brightness)B mode 2D (B brightness)
» Harmonic imaging – octave mode
• Doppler modes:– Doppler spectrum– Color doppler– (Strain)– (Strain)
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A-scan (obsolete)A scan (obsolete)• Figure 1 The pulse-echo principle is
used to produce an ultrasound A-scan. • A pulse is emitted from the transducer• A pulse is emitted from the transducer
at the same time as a dot is set in motion from left to right on the A-scan screen.
• When an echo reaches the transducer, the received signal causes a verticalthe received signal causes a vertical deflection of the trace.
• The distance between deflections on the A-scan corresponds to the depth of the interface from the transducer.
• Peter N Burns: INTRODUCTION TO THE PHYSICAL PRINCIPLES OF ULTRASOUND IMAGING AND DOPPLER November 2005DOPPLER, November 2005
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M-mode (M=motion) ≈ echo sounderM mode (M motion) ≈ echo sounder
Depth
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TimeIll.: B. Angelsen, NTNU
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HeartM-modeM mode
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Pulse Repetion FrequencyPulse Repetion Frequency• d = Attenuation/(2··f), where = 0.5 dB/cm/MHz• Max depth, example: d=23.1 cm, c=1540 m/s• Time to travel up and down: T = 2d/c = 0.3 ms• Pulse Repetition Frequency PRF = 1/T = 3333 Hz• PRF = Framerate for A- and M-modes• Too high PRF => Spatial ”aliasing”:
Tx pulse 1 23.1 cm Strong echo @ 25 cm
Tx pulse 2
Time/2-way range, pulse 1
Time/2-way range, pulse 2
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Multiple beams are sentto scan the entire volume
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Frame rate in 2DFrame rate in 2D• From before: A-scan:
– Max depth d=23.1 cm, PRF = c/(2d)= 3333 Hz
• Typical beamwidth (cardiac probe): =/d = 0 5mm/19mm = 0 026 rad = 1 5o=/d = 0.5mm/19mm = 0.026 rad = 1.5o
• Desired sector size: Θ=90o
• Beam distance (p=25 50% of beamwidth): p 1 5o=0 5o• Beam distance (p=25-50% of beamwidth): p·1.5o=0.5o
• No of beams per image: N=Θ/p·90o/0.5o = 180 Frame rate: FR = PRF/N = 3333/180 = 18 5 Hz fps• Frame rate: FR = PRF/N = 3333/180 = 18.5 Hz, fps
– Analog TV: 50 half-frames per second
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Parallel beamforming – multiple line acquisitionline acquisition• Principle: use wider
transmit beam and several, M, parallel
i b freceive beamformers• Previous ex. with M=4:
– N=Θ/(M·p·)= 90o/2o = 45– FR = 3333/45 = 74 Hz, fps
Fig. from Synnevåg, Austeng, Holm, ”Benefits of Minimum-Variance Beamforming in Medical Ultrasound Imaging”, IEEE Trans. Ultrason., Ferroelect., Freq. Contr., Sept. 2009.
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2D framerate2D framerate • Assume a fixed aperture, D; a fixed maximum attenuation before
next ping A; and that attenuation varies linearly with frequencynext ping, A; and that attenuation varies linearly with frequency– PRF = 1/T = c/2d. – d = A/(2··f), where = 0.5 dB/cm/MHz, and A is max attenuation => PRF = c·α·f/A
• Angular distance between receiver beams: = p/D, where p is g p pthe percentage shift relative to a beamwidth (p = 25-50% typ)
– M = no of parallel rx beams, M= tx/, ratio of tx and rx beamwidths
• Angular sector to be covered:
• Number of beams: N = /tx = /M = D/pM• FR = PRF/N = cfpM/(AD) = pMc2/(A D)
I d d t f f ith th ti– Independent of frequency with these assumptions– Explananation: As frequency increases, frame rate decreases due to narrower
beams. This cancels the increase in PRF due to a smaller depth.
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• Doppler • 3D
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G. York, Y. Kim , Ultrasound Processing andComputing: Review and Future DirectionsAnnu. Rev. Biomed. Eng. 1999
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Medical UltrasoundMedical Ultrasound1. Introduction2. Ultrasound instruments3. Main principles4 Imaging modes4. Imaging modes5. Probe types and image
formats6. Bioeffects and safety7. Emerging technology
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Sector scanSector scan• Small footprint:
A th h ib f– Access through ribs for cardiology
– Typ: 19 mm adult, <12 mm pediatrypediatry
• Started with mechancially tilted probes (figure from B. Angelsen NTNU)Angelsen, NTNU)
• Now: phased multi-element arrays and electronic tilting by meanselectronic tilting by means of digital delays
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Linear scanLinear scan• Beam is moved along
probe surface by switchingprobe surface by switching elements in and out
• Can be done with simple electronics (important inelectronics (important in the 80’s)
• Suitable for organs with good access, e.g. external g , gorgans:
– Artery in neck (halspulsåre)– Thyroid (Skjoldbrukskjertel)– Muscles, tendons
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Curvilinear scanCurvilinear scan• Beam is scanned along
probe surface like linearprobe surface like linear scan
• Results in a large sector i d ith d timaged with moderate requirements on access
• Used for – Fetal imaging– Internal organs: kidney, liver– Breast …
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Ill.: B. Angelsen, NTNU
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Factors which determine frame rateFactors which determine frame rate• Depth where attenuation reaches e.g. ~60 dB
– Attenuation = 2d··f– Example: 60 dB attenuation ( = 0.5 dB/cm/MHz):
» f = 2.6 MHz: d = 23.1 cm depth p
• Speed of sound• Number of transmit beams in M-, 2-D, or 3-D , ,
modes• Recap 1-D and 2-D framerate on next slides
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Pulse Repetion FrequencyPulse Repetion Frequency• Max depth, example: d=23.1 cm, c=1540 m/s
• Time to travel up and down: T = 2d/c = 0.3 ms
• Pulse Repetition Frequency PRF = 1/T = 3333 Hz
• PRF = Framerate for A- and M-modes
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Frame rate in 2DFrame rate in 2D• Previous A-scan:
– Max depth d=23.1 cm, PRF = c/(2d)= 3333 Hz
• Typical beam width (cardiac probe): /d = 0 5mm/19mm = 0 026 rad = 1 5o/d = 0.5mm/19mm = 0.026 rad = 1.5o
• Beam distance (typ 25-50% of bw, here 1/3): 0.5o
• Desired sector size: 90o• Desired sector size: 90o
• Number of tx beams per image: N=90o/0.5o = 180 – Frame rate: FR = PRF/N = 3333/180 = 18 5 Hz or fps– Frame rate: FR = PRF/N = 3333/180 = 18.5 Hz or fps
• No of parallel receive beams: M=4 => N=180/4=45 – Frame rate FR = PRF/N = 3333/45 = 74 fps (frames per second)
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p ( p )
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3D frame rate3D frame rate• Prev. 2D ex: FR2D = PRF/N = 3333/180 = 18.5 Hz• Extend to 3D with perpendicular 90o sector and
beam distance 0.5o: FR3D = FR2D /180 = 0.1 volumes per secondp
• The fundamental 3D frame rate problem:– Speed of sound is too low!
B tt t h i k t t 30 i b th di i• Better to shrink sector to 30o in both dimensions and use 4x4 parallel beams: FR3D = 0.1·3·3·4·4= 14.4 volumes per second
– Low, but OK– The trend is to increase no of parallel beams
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Medical UltrasoundMedical Ultrasound1. Introduction2. Ultrasound instruments3. Main principles4 Imaging modes4. Imaging modes5. Probe types and image
formats6. Bioeffects and safety7. Emerging technology
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Bioeffects and SafetyBioeffects and Safety• Thermal effects: heating of muscles, tendons (physiotherapy)
M h i l ff t hi f kid / ll t• Mechanical effects: crushing of kidney/gall stones, surgery• All instruments display TI and MI• TI – Thermal Index: estimate of heating in hottest part of beam
– TIS - Thermal Index Soft tissue: the most usual one– TIB - Thermal Index Bone: for bone in focal point (fetal scan)– TIC - Thermal Index Cranial: bone at probe surface (cranial imaging)
TI 1 5 ti d i id d f dl f ti– TI <1.5 centigrade is considered safe regardless of exposure time
• MI - Mechanical Index. MI = p-/f0.5 < 1.9– Risk of cavitation (sometimes called cavitation index)– Peak negative pressure in MPa– Frequency in MHz
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Medical UltrasoundMedical Ultrasound1. Introduction2. Ultrasound instruments3. Main principles4 Imaging modes4. Imaging modes5. Probe types and image
formats6. Bioeffects and safety7. Emerging technology
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Emerging technologyEmerging technology• 3D ultrasound:
– Not really emerging, but still quite new
• ElastographyC• Contrast agents
– Targeted ultrasound imaging– Ultrasound-assisted drug deliveryUltrasound assisted drug delivery
• Ultrasound tomography
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Tissue: about 70% water
compression shearcompression
probing of the mechanicalstructural propertiesstructural propertiesof the SOLID componentsrequires the application ofSHEAR d f i
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SHEAR deformationRalph Sinkus
UNIVERSITETET I OSLO
E
Palpation and Elasticity in human soft tissues
µ 23E
Young’s Modulus EEµµ
23
2 other mechanical coefficients are commonly used for defining the elasticity of a solid material
~ Bulk Compression Modulus, almost constant, of the order of 109 Pa,
µ Shear Modulus, Strongly heterogeneous, varying between
102 and 107 Pa
>> ⇒ E 3 µ
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Mickael Tanter
UNIVERSITETET I OSLO Mechanical waves in soft tissues
Compressional Waves propagate at
Sh t t
2
Pc ( 1500 m.s-1)
Shear waves propagate at
sc ( 1-10 m.s-1)
Two kind of waves propagating with totally different speeds !!
Shear waves propagate only at low frequencies < 1000 Hz
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p p g y q
Mickael Tanter
UNIVERSITETET I OSLO
General Concept of ElastographyGeneral Concept of Elastography• Deform your object in some way• Measure deformation and/or the waves
by an imaging techniqueMRI Ult d– MRI, Ultrasound
• Find mechanical properties– Strain ² = σ/EStrain, ² σ/E– Shear modulus, E - as a function of frequency
» Measure wave speed, cs = (μ/ρ)0.5 ≈ (E/3ρ)0.5
» or invert wave equation– Can also find attenuation ~ imag. part of E
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Ultrasound methodsUltrasound methods1. Static2. Transient3. Internal stimulus4. Acoustic streaming = acoustic radiation force
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1 Static Elastography1. Static Elastography
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1 Static Elastography1. Static ElastographyNow offered by several vendors:
• GE's LOGIQ E9 ultrasound elastography
• Siemens eSie Touch™ elasticity imaging
• Hitachi Real-time Tissue Elastography (HI-RTE) based on ultrasound
– breast, prostate, thyroid and pancreatic disease
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UNIVERSITETET I OSLO 2. Transient Elastography2. Transient Elastography
~ 20 ms
100 ms
Shear wave generation + Ultrafast Imaging
TimeLow Frequency « punch »(50 Hz 2 cycles)
~ 1 ms
(50 Hz, 2 cycles)
Acquisition of RF signalsstored
In memories(ultrasound pulsed(ultrasound pulsedexcitation at 4 MHz)
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Fibroscan: Echosens ParisFibroscan: Echosens, Paris
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3 Internal stimulus3. Internal stimulus • Philips iU22 xMATRIX ultrasound
tsystem• Advanced Breast Tissue Specific
Imaging (TSI)Imaging (TSI)• Elastogram generated from internal
patient movementpatient movement– breathing – cardiac motion
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UNIVERSITETET I OSLO 4. Remote Palpation usingp g
the Ultrasonic Radiation force
Ultrasound Transducer
Focal zone ),(),( 22 trptrF
Imaged
Force
),(),( 2 pc
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Area
A . Sarvazyan, K Nigthingale, J Greenleaf, M. Fink, M Tanter
UNIVERSITETET I OSLO
Approved systemsApproved systems• Supersonic Imagine:
– 2009: FDA clearance for Aixplorer® Ultrasound System, with Real-Time, SuperSonic ShearWave Elastography (SWE).
– 2012: FDA clearance for the addition of a Real-Time, Adjustable Numerical Scale in meters per second (ANSTM)
• Simens: Approved by FDA 2013: Virtual Touch Implementation of– Approved by FDA 2013: Virtual Touch - Implementation ofAcoustic Radiation Force Impulse (ARFI) technology.
FDA = Food Drug Administration, USA
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UNIVERSITETET I OSLO Breast Cancer Examples
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UNIVERSITETET I OSLO In vivo assessment of carotid plaque elasticity
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UNIVERSITETET I OSLO
Hypothesis: Presence of chaotic vascular tree in tumors leads to altered dispersiontree in tumors leads to altered dispersion and enhanced apparent viscosity
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Normal vs fractal distribution of scatterersNormal vs fractal distribution of scatterersTop: Usual assumption: PDF is a
“normal” distributionnormal distribution.
Bottom: Much data from the natural world consists of an ever larger number of ever smaller values The PDF is asmaller values. The PDF is a fractal distribution.
J Garnier and K SølnaJ. Garnier and K. Sølna, “Effective fractional acoustic wave equations in one-dimensional random Liebovitch and Scheurle, Two lessons
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multiscale media," JASA, Jan 2010. 80
from fractals and chaos, Complexity, 2000
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Elastography - conclusionsElastography conclusions• Shear waves probe elasticity and correlate better with
palpation than conventional ultrasoundpalpation than conventional ultrasound• Shear wave described by:
– Young’s modulus E ≈ 3 – Shear modulus complex shear modulus G*= Gd+ i Gl
– Speed of propagation c2 = /
• Ultrasound based elastography: g p y– Static, dynamic, breathing/heart, acoustic streaming (supersonic)
• MR-based elastographyF ti l t i t l ti hi l i l• Fractional strain-stress relationship can explain power lawbehavior of shear waves
• Hypothesis: Spatial models are even better
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LiteratureLiterature• Jean Pope, Medical Physics: Imaging, chapter 1
Ult d 5 27 1999Ultrasound, pp. 5-27, 1999• Wells, P. N. T. "Ultrasound imaging." Physics in
medicine and biology 51 13 (2006): R83medicine and biology 51.13 (2006): R83.• Wells, Peter NT, Hai-Dong Liang, and Terry P.
Young. "Ultrasonic imaging technologies inYoung. Ultrasonic imaging technologies in perspective." Journal of Medical Engineering & Technology 35.6-7 (2011): 289-299
• Sverre Holm, Medisinsk ultralydavbildning, 2008
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