Lesson 07 - Sonicor Incsonicorinc.com/images/Lesson_07_2010.pdf · plus 16 multiple-choice ......

This lesson was derived

from pages 33 through 42

in the textbook:

Lesson 07:

Ultrasound Transducers

This lesson contains 72 slides

plus 16 multiple-choice

questions.


Real-time B-mode systems may use transducers that produce images that are

displayed in linear formats, which represent sections of the scanned structures

as either rectangles (standard linear) or parallelograms (steered linear). The

linear format is created by sequentially transmitting a series of acoustic lines,

each in a direction that is parallel to the previous acoustic line. Each acoustic

line is generated by a single sound pulse leaving the transducer.


Some transducer configurations produce B-scan images in a sector format.

The sector format displays wedge-shaped sections, that are categorized as pie-

shaped, blunted-pie, or trapezoidal. The sector format is created by

transmitting a series of acoustic lines, each at an angle that is different from

that of the previous acoustic line.


Linear images have the same field-of-view in both the near field, the area in a

patient that is near the face of the transducer, and in the far field, the area in a

patient that is farthest from the face of the transducer.

field-of-view: the

scanning plane visible

from a specific

transducer configuration


Sector images have a limited field-of-view in the near field, but the field-of-view

in the far field is usually greater than that of a linear image. Also, spaces

between individual acoustic lines in the far field are greater than in the near

field, but interpolation in the image is used to overcome this disadvantage.


A real-time B-scan ultrasound image is updated many times a second to

produce the live display. Temporal resolution is a function of the real-time

frame rate, which represents how often updating occurs. A low frame rate

(lower temporal resolution) is acceptable for abdominal imaging since there is

not much movement of the scanned structures. Temporal variations may be

lessened by using frame averaging, which is the addition of consecutive

frames.


For a flicker-free real-time image, the frame rate should be at least 10 to 15 Hz.

Low frame rates allow an increase in the number of acoustic lines, the

individual sound beams that are produced throughout the scanned cross-

section. Image quality is a function of line density, which is proportional to the

number of acoustic lines.

THE NUMBER OF ACOUSTIC LINES

IN A REAL TIME IMAGE:

PULSE REPETITION FREQUENCY

FRAME RATE


Higher frame rates (higher temporal resolution) must be used for

echocardiography because of the rapid movements of structures in the heart,

but the use of higher frame rates, however, may result in reduced image quality

due to the reduction in the number of acoustic lines.




FRAME RATE


Some manufacturers have been able to use high frame rates and still achieve

what appears to be increased line density. The high frame rates in these

systems produce fewer acoustic lines but each line is sampled multiple times

during the receive mode from different angles, effectively increasing the

number of displayed lines.




FRAME RATE


Depending on the system, frame rates can be fixed or operator-selectable or

can vary automatically. Frame rates that vary automatically often depend on

the transducer frequency, the display depth, and focal-zone settings.




FRAME RATE


A decrease in the DISPLAY DEPTH setting increases the pulse repetition

frequency (PRF) to produce an increase in the number of acoustic lines. High

PRF values usually result in depth ambiguity, which decreases the maximum

depth that can be accurately imaged. To prevent depth ambiguity, a high PRF

is only possible when the display depth is decreased.




FRAME RATE


Decreasing the angle of a sector display, while not actually changing the

number of acoustic lines, increases the line density without affecting the

temporal resolution. Line density affects spatial resolution, but does not affect

lateral resolution.

PRF ÷ FRAME RATE = ACOUSTIC LINES

1000 Hz 10 Hz 100

1000 Hz 20 Hz 50

1500 Hz 10 Hz 150

1500 Hz 20 Hz 75

2000 Hz 10 Hz 200

2000 Hz 20 Hz 100

ACOUSTIC LINES = PRF ÷ FRAME RATE


ACOUSTIC LINES = PRF ÷ FRAME RATE

DISPLAY

DEPTH

PRF CHANCE OF

DEPTH

AMBIGUITY

FRAME RATE ACOUSTIC

LINES

Increase Decrease Decrease ——–—-—- Decrease

Decrease Increase Increase —————- Increase

—————— —————— —————— Increase Decrease

—————— —————— —————— Decrease Increase

Flat-linear array

Linear scanning formats are produced by flat-linear array transducers. The flat-

linear array (often identified as linear array without the ―flat‖ classification)

contains a large number of linearly arranged piezoelectric elements. The

elements, which are pulsed sequentially produce parallel acoustic lines to form

a rectangular or parallelogram shaped image.

CONVENTIONAL LINEAR ARRAY

PHOTO OF LINEAR ARRAY

The linear scanning format displays a large field-of-view of structures close to

the transducer. However, the transducer’s large surface area, or footprint,

often makes it difficult to obtain images of structures that are located beneath

obstructions, such as the heart, which is located beneath the ribs. Flat-linear

array transducers can be used for abdominal, obstetrical, small parts, vascular,

and musculoskeletal imaging.

footprint: the footprint is

the region on the face of

an ultrasound

transducer that is in

contact with the patient

PHOTO OF LINEAR ARRAY LINEAR ARRAY SLICE PATTERN

Flat-linear array

Flat-linear array

CONVENTIONAL LINEAR ARRAY FETAL IMAGE

Flat-linear array

CONVENTIONAL LINEAR ARRAY BREAST IMAGE

Flat-linear array

UMBILICAL CORD WITH COLOR DOPPLER

Flat-linear array

Flat-linear array

THYROID AND LEFT CAROTID

TRANSMIT

FOCAL

ZONES

Flat linear arrays, like other arrays, have selectable ―transmit focal zones‖ for

lateral resolution improvement along the ―two-dimensional‖ multiple-element

plane.

Flat-linear array

A linear transducer may be configured as a ―multi-dimensional array (also

called 1.5 dimensional array), with a matrix of elements along the ―width‖ plane

(often called ―elevation or z-axis‖) to improve elevational resolution by reducing

the slice thickness, often called ―section thickness.‖ A reduced slice thickness

decrease chances of a tissue averaging artifact.

MULTI-DIMENSIONAL LINEAR ARRAY

ELEMENT CONFIGURATION

Flat-linear array

Flat-linear array

STEERED LINEAR ARRAY VASCULAR IMAGE

Flat-linear array (Steered)

PROSTATE

Flat-linear array

Curved-linear array

A sequentially pulsed transducer that produces a real-time sector image is the

curved-linear array, which is often called curvilinear array or convex array.

PHOTO OF CURVED-LINEAR ARRAY

Similar to the flat-linear array, a curved-linear array also contains a large

number of linearly arranged piezoelectric elements. Since the surface of the

curved-linear array is not flat, each acoustic line is transmitted at an angle,

which is different from that of the previous acoustic line.

CURVED-LINEAR ARRAY ELEMENT CONFIGURATION

Curved-linear array

Depending on the transducer’s footprint, the field-of-view in the near field could

be much greater than that of many other sector transducer configurations.

Curved-linear array transducers can be used for abdominal, obstetrical,

gynecological, and small parts imaging.

CURVED-LINEAR ARRAY SLICE PATTERN

Curved-linear array

Curved-linear array

LIVER AND RIGHT KIDNEY

Curved-linear array

ABDOMEN WITH COLOR DOPPLER

Curved-linear array

Curved-linear array

FIBROID UTERUS

Curved-linear array

Curved-linear array

LIVER – HEPATIC VESSELS

ASCITES

Curved-linear array

ENDOVAGINAL PROBE

Curved-linear array

ENDOVAGINAL

PROBE

TRANSABDOMINAL

PROBE

Sagittal scan planes

ENDOVAGINAL UTERUS

Curved-linear array

PROSTATE IMAGE

Curved-linear array

NEONATAL BRAIN IMAGE

Curved-linear array

Curved-linear array

HANDHELD ULTRASOUND SCANNER

Phased array

Sector real-time imaging is also possible with a phased array transducer, which

contains a large number of linearly arranged piezoelectric elements along a

small scanning surface.

PHOTO OF PHASED ARRAY

The sweeping, or steering, of each acoustic line is performed electronically by

pulsing all of the elements in the array as one group, but with small time or

phase differences between them.

Phased array

The footprint of a phased array transducer is small compared to the curved-

linear array, and the pie-shaped image that is produced has a more limited

field-of-view in the near field.

PHASED ARRAY SLICE PATTERN

Phased array

Phased array

ABDOMEN

Phased array

FETAL HEAD

Phased array

Phased array

ENDOVAGINAL UTERUS

Phased array

Phased array

CARDIAC IMAGE

Phased array

TRANSESOPHAGEAL

ECHOCARDIOGRAPHY

Phased array

PROSTATE IMAGE

Phased array

Vector array

Some manufacturers of ultrasound equipment provide compound array

transducers, which combine flat sequenced linear array and phased array

techniques to provide a trapezoidal imaging format.

PHOTO OF VECTOR ARRAY

The footprint of a compound array (often termed trapezoidal array or vector

array) transducer is slightly larger than that of a normal phased array

transducer, and the sector image that is produced has a wider field-of-view in

the near field. Phased arrays and compound arrays are routinely used for

echocardiography, abdominal, pelvic, vascular, transcranial, and neonatal brain

imaging.

VECTOR ARRAY SLICE PATTERN

Vector array

ABDOMEN

Vector array

HEART, 4-CHAMBER VIEW

Vector array

CAROTID ARTERY

Vector array

Transducer arrays

Flat-linear array, curved-linear array, phased array, and trapezoidal array

transducers have no moving parts. They can be rapidly switched back and

forth between different modes of operation to provide simultaneous display

modes including real-time only, real-time with M-mode or real-time with

Doppler. Additionally, transducers containing arrays have electronic transmit,

receive, and dynamic ―beam forming‖ capabilities, which aid in the

improvement of resolution. Most arrays also use acoustic lenses to further

improve elevational resolution.

Mechanically steered

Mechanical transducers, described as a transducer filled with a fluid and

containing a motor, may also create real-time images.

The motor rotates or sweeps a piezoelectric element through an arc to transmit

acoustic lines that travel at different angles to produce a live sector image.

Only a few ultrasound systems use this transducer configuration, which is

relatively low in cost.

Mechanical wobbler

Unlike transducer configurations that do not contain moving components,

mechanical transducers cannot provide simultaneity of live displays (live 2-D

with live M-mode or live 2-D with live spectral Doppler).

Mechanical wobbler

SINGLE-ELEMENT ANNULAR ARRAY

Some mechanically steered transducers contain annular arrays, which, like

linear and phased arrays, can be electronically focused. This aids in the

improvement of resolution by providing a greater depth-of-focus with slice

thickness equal to beam width.

annular array: a

configuration consisting of

concentric, ring-shaped

piezoelectric elements that

are used in some

mechanically steered

sector transducers

Mechanical wobbler

HEPATIC VEINS


EYE, DETACHED RETINA


USB powered

A recently introduced scanner configuration defined as ―USB powered‖ uses

self-contained probes that can be plugged into the USB port of a PC (e.g.,

laptop, notebook, tablet, PDA) either directly or through an adapter. The probe

or adapter contains all the electronics needed to drive the transducer and

process the returning echoes.

CURVED LINEAR ARRAY

TRANSDUCER AND USB

ADAPTER

USB POWERED

MECHANICALLY STEERED

PROBE

TRANSDUCER WITH A BUILT-IN FLUID DELAY

Fluid-delay

A fluid-delay or stand-off may be used with any transducer configuration to

permit better visualization of superficial structures.

A transducer may have a built-in fluid delay, or a reusable or disposable stand-

off pad may be used.

FLAT-LINEAR ARRAY TRANSDUCER WITH A

REUSABLE EXTERNAL STAND-OFF PAD

Fluid-delay

Answers to the following

SIXTEEN practice

questions were derived

from material in the

textbook:

Question 1

For a real time image to be flicker-free, the minimum

image frame rate should be

15 Hz

1000 Hz

1 Hz

100 Hz

1 MHz

Page 34

If the real time frame rate is 20 Hz, the

pulse repetition period is 1/20 second

image is updated every 1/1000 second

number of acoustic lines is 1000

number of acoustic lines is 20

image is updated every 1/20 second

Question 2

Page 34

If the real time frame rate is increased but the lines

per frame are unchanged, what else must happen?

speed of sound increases

imaging depth increases

transducer frequency increases

the pulse repetition frequency decreases

imaging depth decreases

Question 3

Page 34

If the lines per frame changed but the imaging depth

remained the same, what else must have changed?

frame rate

pulse repetition period

pulse repetition frequency

duty factor

resolution

Question 4

Page 34

If the imaging depth is increased and the sector

angle and line density remain the same, what must

have taken place?

PRF increases

transducer frequency increases

frame rate decreases

PRP decreases

frame rate increases

Question 5

Page 34

A real time transducer with a frame rate of 10 Hz produces

100 acoustic lines. If the PRF is NOT changed,

a higher frame rate will increase the line density

a frame rate of 20 Hz will produce 200 acoustic lines

a lower frame rate results in more updated images

per second

the pulse repetition period is 100 milliseconds

a frame rate of 20 Hz will produce 50 acoustic lines

Question 6

Page 34

Which transducer configuration produced the image?

flat linear array

curved linear array

convex array

phased array

vector array

Question 7

Pages 35 and 36


flat linear array

curved linear array

convex array

phased array

vector array

Question 8

Pages 39 and 40


flat linear array

curved linear array

non-curved linear array

phased array

vector array

Question 9

Pages 37 and 38


flat linear array

curved linear array

non-curved linear array

phased array

vector array

Question 10

Pages 39 and 40

Dynamic focusing is possible

only with transducers with frequencies above 5 MHz

when the dynamic range is maximum

only with transducer arrays

with two-element CW Doppler probes

with single piezoelectric elements

Question 11

Page 41

With phased array transducers, the transmitted sound

beam is swept by

mechanically sweeping the piezoelectric elements

mechanically rotating the piezoelectric elements

varying the timing of pulses to the individual

piezoelectric elements

varying the voltage of pulses to the individual


varying the frequency of pulses to the individual


Question 12

Page 39

Which pulsing pattern provides an on-axis beam with

focusing?

Question 13

Page 39

The use of a water path permits

the use of increased output power from the transducer

higher frequencies to be used

higher duty factors

higher pulse repetition frequencies to be used

better visualization of superficial structures

Question 14

Page 42

Which element arrangement would only be used in

mechanically steered transducers?

phased linear array

convex array

non-curved sequenced array

sequenced array

annular array

Question 15

Page 41

The advantage of an annular array over a single

element transducer is

reduced output power from the transducer

higher frequencies are possible

improved axial resolution

greater depth of focus

lower cost

Question 16

Page 41

END OF LESSON 07

Lesson 07 - Sonicor Incsonicorinc.com/images/Lesson_07_2010.pdf · plus 16 multiple-choice ......

Documents

Transcript of Lesson 07 - Sonicor Incsonicorinc.com/images/Lesson_07_2010.pdf · plus 16 multiple-choice ......