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SECTION 1: ULTRASOUND PHYSICS FUNDAMENTALS (35 Questions)
Q1. A sonographer is reviewing the properties of sound waves. Which of the following
correctly describes the relationship between frequency and wavelength in soft tissue?
A. Frequency and wavelength are directly proportional; as frequency increases,
wavelength increases
B. Frequency and wavelength are inversely proportional; as frequency increases,
wavelength decreases [CORRECT]
C. Frequency and wavelength are unrelated; changing one does not affect the other
D. Wavelength is always twice the frequency in soft tissue
Rationale: On the ARDMS SPI exam, remember that propagation speed equals
frequency times wavelength (c = f × λ). Since propagation speed in soft tissue is
,constant at 1540 m/s, frequency and wavelength must be inversely related. Higher
frequency means shorter wavelength, which is why high-frequency transducers give
better resolution but less penetration.
Correct Answer: B
Q2. A sonographer measures the pulse duration of a transducer and finds it to be 1.5
microseconds. The spatial pulse length is 2.31 mm. What is the propagation speed of
sound in the tissue being examined?
A. 1450 m/s
B. 1540 m/s [CORRECT]
C. 1620 m/s
D. 1780 m/s
Rationale: That's right because of the physics principle that propagation speed equals
spatial pulse length divided by pulse duration. Convert units: 2.31 mm = 0.00231 m, and
1.5 μs = 0.0000015 s. So 0.00231 ÷ 0.0000015 = 1540 m/s. On the ARDMS SPI exam,
remember that 1540 m/s is the assumed average propagation speed in soft tissue, and
this calculation confirms it.
Correct Answer: B
,Q3. Which property of a sound wave is determined by the source and does NOT change
as the wave travels through different media?
A. Propagation speed
B. Wavelength
C. Frequency [CORRECT]
D. Amplitude
Rationale: On the ARDMS SPI exam, remember that frequency is determined by the
transducer crystal and remains constant regardless of the medium. Propagation speed,
wavelength, and amplitude all change as sound travels through different tissues.
Frequency is the one property that stays locked to what the transducer generates.
Correct Answer: C
Q4. A sonographer is comparing two transducers. Transducer A operates at 3.5 MHz,
and Transducer B operates at 7.0 MHz. If both are imaging the same tissue, which
statement is correct?
A. Transducer A will produce images with better axial resolution and less penetration
, B. Transducer B will produce images with better axial resolution and less penetration
[CORRECT]
C. Both transducers will have identical resolution and penetration characteristics
D. Transducer B will have deeper penetration but poorer resolution than Transducer A
Rationale: A common SPI trap is confusing the frequency tradeoffs. Higher frequency
(7.0 MHz) gives better axial resolution because the spatial pulse length is shorter, but
the attenuation coefficient is higher, so penetration is reduced. Lower frequency (3.5
MHz) penetrates deeper but with poorer resolution. The correct adjustment for better
resolution is always higher frequency, but you pay the price in depth.
Correct Answer: B
Q5. The amplitude of an ultrasound pulse decreases from 80 mW/cm² to 20 mW/cm²
after passing through tissue. What is the attenuation in decibels?
A. 3 dB
B. 6 dB
C. 12 dB [CORRECT]
D. 18 dB