Lesson 07 - Sonicor Incsonicorinc.com/images/Lesson_07_2010.pdf · plus 16 multiple-choice ......
Transcript of 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.
Ultrasound Transducers
Ultrasound Transducers
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.
Ultrasound Transducers
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.
Ultrasound Transducers
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
Ultrasound Transducers
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.
Ultrasound Transducers
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.
Ultrasound Transducers
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
Ultrasound Transducers
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.
THE NUMBER OF ACOUSTIC LINES
IN A REAL TIME IMAGE:
PULSE REPETITION FREQUENCY
FRAME RATE
Ultrasound Transducers
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.
THE NUMBER OF ACOUSTIC LINES
IN A REAL TIME IMAGE:
PULSE REPETITION FREQUENCY
FRAME RATE
Ultrasound Transducers
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.
THE NUMBER OF ACOUSTIC LINES
IN A REAL TIME IMAGE:
PULSE REPETITION FREQUENCY
FRAME RATE
Ultrasound Transducers
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.
THE NUMBER OF ACOUSTIC LINES
IN A REAL TIME IMAGE:
PULSE REPETITION FREQUENCY
FRAME RATE
Ultrasound Transducers
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
Ultrasound Transducers
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
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
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
Mechanically steered
Mechanically steered
EYE, DETACHED RETINA
Mechanically steered
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
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 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 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 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
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
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
Which transducer configuration produced the image?
flat linear array
curved linear array
convex array
phased array
vector array
Question 7
Pages 35 and 36
Which transducer configuration produced the image?
flat linear array
curved linear array
convex array
phased array
vector array
Question 8
Pages 39 and 40
Which transducer configuration produced the image?
flat linear array
curved linear array
convex array
phased array
vector array
Question 8
Pages 39 and 40
Which transducer configuration produced the image?
flat linear array
curved linear array
non-curved linear array
phased array
vector array
Question 9
Pages 37 and 38
Which transducer configuration produced the image?
flat linear array
curved linear array
non-curved linear array
phased array
vector array
Question 9
Pages 37 and 38
Which transducer configuration produced the image?
flat linear array
curved linear array
non-curved linear array
phased array
vector array
Question 10
Pages 39 and 40
Which transducer configuration produced the image?
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
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
piezoelectric elements
varying the frequency of pulses to the individual
piezoelectric elements
Question 12
Page 39
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
piezoelectric elements
varying the frequency of pulses to the individual
piezoelectric elements
Question 12
Page 39
Which pulsing pattern provides an on-axis beam with
focusing?
Question 13
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
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
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
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