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ultrasound physics exam review final chapter 13 to 24Questions With Complete Solutions
392. Which of the following will improve a system's temporal
resolution?
A. increased sector angle
B. increased line density
C. increased PRF
D. increased frequency Correct Answer C. To improve
temporal resolution, increase the number of images produced
each second. If the number of pulses emitted per second is
increased (choice C) then the system can increase the frame rate.
Increased PRF is obtained by decreasing the maximum imaging
depth. A, B, and D all decrease frame rate and decrease temporal
resolution.
393. True or False? An ultrasound system with a longer pulse
duration will generally have better temporal resolution. Correct
Answer False. Temporal resolution of a system is unaffected by
the pulse duration.
394. True or False? The length of a pulse does not directly
influence the temporal resolution. Correct Answer True.
Temporal resolution is not affected by the length of the pulses
produced by the system. The factors that influence the temporal
resolution are maximum imaging depth, sector angle, line
density, and the number of foci per scan line.
395. Two imaging systems produce acoustic pulses; one pulse is
0.4 usec long and the other is 0.2 usec long. Which is most
likely to provide the best temporal resolution?
,A. 0.4 usec system
B. 0.2 psec system
C. they are the same
D. cannot be determined Correct Answer D. Temporal
resolution is unrelated to pulse duration. Temporal resolution is
determined by the number of frames, or images, that are
produced each second. There is insufficient information to
answer the question.
396. Which two factors determine temporal resolution?
A. speed of sound and depth of view
B. pixel size and sector size
C. focal zones and sector depth
D. propagation speed and frame rate Correct Answer A. Of the
4 choices, propagation speed and depth of view have the greatest
effect upon frame rate and temporal resolution. Frame rate is
high with shallow imaging. Frame rate is high when sound
travels quickly in a medium.
397. Which two controls determine a system's temporal
resolution?
A. frame rate and sector size
B. focal zones and sector depth
C. propagation speed and frame rate
D. depth of view and pulses per image Correct Answer D.
Depth of view and number of pulses per image determine the
frame rate (and temporal resolution) of an ultrasound system.
The sonographer can alter both of these factors.
398. True or False? An ultrasound system with a shorter pulse
repetition period (PRP) will have better temporal resolution than
,a system with a longer PRP. Correct Answer True. An
ultrasound system with a shorter PRP has the ability to produce
more pulses each second. With more pulses per second, the
system creates many images per second. Increased frame rate
improves temporal resolution.
399. What is the primary disadvantage of multiple focal zones
along each scan line of a two-dimensional image?
A. improved temporal resolution
B. decreased temporal resolution
C. improved lateral resolution
D. improved longitudinal resolution Correct Answer B. With
multiple foci along each scan line, the ultrasound system uses
many pulses to create each image. This reduces the number of
frames created per second. A low frame rate results in decreased
temporal resolution.
400. What is the primary advantage of multiple focal zones
along each scan line of a two- dimensional image?
A. improved temporal resolution
B. decreased temporal resolution
C. improved lateral resolution
D. improved longitudinal resolution Correct Answer C.
Multiple foci along a single scan line creates a composite beam
that is extremely narrow. Narrow sound beams create images
with superior lateral resolution at all depths. Single focus
systems use a single sound beam to create each scan line, and
lateral resolution is optimal at only one depth.
401. Which choice will result in increased frame rate and
temporal resolution? A. decreased propagation speed
, B. decreased sector size
C. decreased lateral resolution
D. decreased pulse repetition frequency Correct Answer B. A
narrower sector diminishes the number of pulses required to
produce each image. Frame rate and temporal resolution
improves when fewer pulses make each image.
402. True or False? With sector scanning, images with greater
detail (spatial resolution) are created when the number of
acoustic pulses per degree of sector is increased. Correct
Answer True. Spatial resolution is improved with more density
is low, gaps may exist between pulses per degree of sector.
When the line adjacent pulses. Reflectors within the gaps will
not accurately appear on the image.
403. An ultrasound system with a 4.0 MHz transducer is used to
image structures as deep as 15 cm. Twenty images are produced
each second, each requiring 100 acoustic pulses. What is the
PRF of the system?
A. 1,500 Hz
B. 300 Hz
C. 2,000 Hz
D. 4 MHz Correct Answer C. Pulse repetition frequency is
defined as the number of pulses produced by anultrasound
system in one second. In this example, 100 pulses are required
to construct a single image, and 20 images are displayed each
second. Thus, a total of 2,000 pulses are each second to meet the
imaging requirements of this system; this is the PRF. In this
question, frequency and imaging depth are unimportant.
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