, Question 1
A linear array transducer with a 7.5 MHz center frequency and 0.4 mm element
pitch is used for thyroid imaging. If the beam is steered to 30 degrees, what is
the approximate lateral resolution at a depth of 3 cm?
A. 0.4 mm
B. 0.8 mm
C. 1.2 mm
D. 0.2 mm
Correct Answer: B - 0.8 mm
RATIONALE
Lateral resolution for a steered linear array is determined by the beam
width, which increases with steering angle. At 30° steering, the
effective element pitch is pitch / cos() = 0.4 mm / cos(30°) 0.46 mm,
but beam width also depends on depth and aperture; however, the
primary factor is the element pitch divided by the cosine of the
steering angle. The closest approximation among options is 0.8 mm,
reflecting the widened beam profile. Options A, C, and D misrepresent
the effect of steering on lateral resolution.
Question 2
Which of the following best explains why harmonic imaging improves contrast
resolution in obese patients?
A. Harmonic frequencies are generated within the tissue and have lower
attenuation than fundamental frequencies.
B. Harmonic signals are stronger than fundamental signals at greater
depths due to reduced scattering.
C. Harmonic imaging utilizes a narrower beam profile, reducing side
lobes and clutter.
D. Harmonic frequencies are less affected by phase aberration and have
higher signal-to-noise ratio.
Correct Answer: C - Harmonic imaging utilizes a narrower beam
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,profile, reducing side lobes and clutter.
RATIONALE
Tissue harmonic imaging exploits the nonlinear propagation of
ultrasound to generate harmonics at twice the fundamental frequency.
These harmonics are primarily generated in the main beam, resulting
in a narrower effective beam with fewer side lobes and reduced
clutter, which improves contrast resolution. Option A is incorrect
because harmonics actually have higher attenuation. Option B is false
because harmonic signals are weaker overall. Option D is partially
true but not the primary mechanism for contrast improvement.
Question 3
In spectral Doppler, which parameter change would most directly correct
aliasing without altering the transmitted frequency or depth?
A. Increase the Doppler angle to 60 degrees.
B. Decrease the pulse repetition frequency (PRF).
C. Increase the packet size.
D. Decrease the Doppler gain.
Correct Answer: A - Increase the Doppler angle to 60 degrees.
RATIONALE
Aliasing occurs when the Doppler shift exceeds half the PRF (Nyquist
limit). Increasing the Doppler angle reduces the frequency shift (since
shift is proportional to cos ), thereby bringing the shift below the
Nyquist limit and eliminating aliasing. Decreasing PRF (B) would
worsen aliasing. Packet size (C) and gain (D) do not directly affect
aliasing.
Question 4
A quality assurance phantom reveals a 2 mm axial resolution at 5 MHz. What
is the most likely cause if the pulse duration is 0.4 microseconds?
A. The spatial pulse length is 0.6 mm, so resolution should be better.
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, B. The axial resolution is limited by the pulse repetition frequency.
C. The axial resolution is determined by the beam width, not pulse
duration.
D. The axial resolution is correctly predicted by pulse duration.
Correct Answer: A - The spatial pulse length is 0.6 mm, so
resolution should be better.
RATIONALE
Axial resolution equals half the spatial pulse length (SPL). SPL =
propagation speed × pulse duration = 1540 m/s × 0.4×10^-6 s = 0.616
mm. Half of that is 0.308 mm, so the measured 2 mm is much worse
than expected. Thus, the phantom measurement suggests a problem,
and option A correctly notes that the theoretical resolution should be
better. Options B, C, and D misstate the determinants of axial
resolution.
Question 5
Which of the following artifacts is most likely to be reduced by using a lower
frequency transducer and increasing the number of focal zones?
A. Mirror image artifact
B. Acoustic shadowing
C. Refraction artifact
D. Comet tail artifact
Correct Answer: C - Refraction artifact
RATIONALE
Refraction artifact occurs when the sound beam changes direction at
an interface with different propagation speeds, causing structures to
appear displaced. Lower frequency and multiple focal zones can
reduce refraction by minimizing beam steering and improving beam
uniformity. Mirror image (A) is due to strong reflectors, shadowing
(B) from attenuating structures, and comet tail (D) from reverberation,
none of which are directly mitigated by these adjustments.
Page 4
A linear array transducer with a 7.5 MHz center frequency and 0.4 mm element
pitch is used for thyroid imaging. If the beam is steered to 30 degrees, what is
the approximate lateral resolution at a depth of 3 cm?
A. 0.4 mm
B. 0.8 mm
C. 1.2 mm
D. 0.2 mm
Correct Answer: B - 0.8 mm
RATIONALE
Lateral resolution for a steered linear array is determined by the beam
width, which increases with steering angle. At 30° steering, the
effective element pitch is pitch / cos() = 0.4 mm / cos(30°) 0.46 mm,
but beam width also depends on depth and aperture; however, the
primary factor is the element pitch divided by the cosine of the
steering angle. The closest approximation among options is 0.8 mm,
reflecting the widened beam profile. Options A, C, and D misrepresent
the effect of steering on lateral resolution.
Question 2
Which of the following best explains why harmonic imaging improves contrast
resolution in obese patients?
A. Harmonic frequencies are generated within the tissue and have lower
attenuation than fundamental frequencies.
B. Harmonic signals are stronger than fundamental signals at greater
depths due to reduced scattering.
C. Harmonic imaging utilizes a narrower beam profile, reducing side
lobes and clutter.
D. Harmonic frequencies are less affected by phase aberration and have
higher signal-to-noise ratio.
Correct Answer: C - Harmonic imaging utilizes a narrower beam
Page 2
,profile, reducing side lobes and clutter.
RATIONALE
Tissue harmonic imaging exploits the nonlinear propagation of
ultrasound to generate harmonics at twice the fundamental frequency.
These harmonics are primarily generated in the main beam, resulting
in a narrower effective beam with fewer side lobes and reduced
clutter, which improves contrast resolution. Option A is incorrect
because harmonics actually have higher attenuation. Option B is false
because harmonic signals are weaker overall. Option D is partially
true but not the primary mechanism for contrast improvement.
Question 3
In spectral Doppler, which parameter change would most directly correct
aliasing without altering the transmitted frequency or depth?
A. Increase the Doppler angle to 60 degrees.
B. Decrease the pulse repetition frequency (PRF).
C. Increase the packet size.
D. Decrease the Doppler gain.
Correct Answer: A - Increase the Doppler angle to 60 degrees.
RATIONALE
Aliasing occurs when the Doppler shift exceeds half the PRF (Nyquist
limit). Increasing the Doppler angle reduces the frequency shift (since
shift is proportional to cos ), thereby bringing the shift below the
Nyquist limit and eliminating aliasing. Decreasing PRF (B) would
worsen aliasing. Packet size (C) and gain (D) do not directly affect
aliasing.
Question 4
A quality assurance phantom reveals a 2 mm axial resolution at 5 MHz. What
is the most likely cause if the pulse duration is 0.4 microseconds?
A. The spatial pulse length is 0.6 mm, so resolution should be better.
Page 3
, B. The axial resolution is limited by the pulse repetition frequency.
C. The axial resolution is determined by the beam width, not pulse
duration.
D. The axial resolution is correctly predicted by pulse duration.
Correct Answer: A - The spatial pulse length is 0.6 mm, so
resolution should be better.
RATIONALE
Axial resolution equals half the spatial pulse length (SPL). SPL =
propagation speed × pulse duration = 1540 m/s × 0.4×10^-6 s = 0.616
mm. Half of that is 0.308 mm, so the measured 2 mm is much worse
than expected. Thus, the phantom measurement suggests a problem,
and option A correctly notes that the theoretical resolution should be
better. Options B, C, and D misstate the determinants of axial
resolution.
Question 5
Which of the following artifacts is most likely to be reduced by using a lower
frequency transducer and increasing the number of focal zones?
A. Mirror image artifact
B. Acoustic shadowing
C. Refraction artifact
D. Comet tail artifact
Correct Answer: C - Refraction artifact
RATIONALE
Refraction artifact occurs when the sound beam changes direction at
an interface with different propagation speeds, causing structures to
appear displaced. Lower frequency and multiple focal zones can
reduce refraction by minimizing beam steering and improving beam
uniformity. Mirror image (A) is due to strong reflectors, shadowing
(B) from attenuating structures, and comet tail (D) from reverberation,
none of which are directly mitigated by these adjustments.
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