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US Physics DMS 600: Diagnostic Medical Sonography
100-Question Advanced Master Bank
Section 1: Properties of Sound Waves
1. If the operating frequency of an ultrasound transducer is reduced by half, what is the
corresponding effect on the spatial pulse length (SPL), assuming the number of cycles
per pulse remains constant?
A) The SPL is reduced to one-quarter of its original value.
B) The SPL is reduced by half.
C) The SPL remains unchanged because it is determined by the damping material.
D) The SPL is doubled.
Elaboration: Spatial Pulse Length is calculated as the number of cycles multiplied by the
wavelength. Because frequency and wavelength are inversely proportional ($c = f \lambda$),
halving the frequency doubles the wavelength, thereby doubling the SPL.
2. Which of the following combinations of medium properties will result in the highest
propagation speed for an acoustic wave?
A) High density and high compressibility.
B) Low density and high stiffness.
C) High density and low stiffness.
D) Low density and high compressibility.
Elaboration: Propagation speed is directly proportional to the stiffness (bulk modulus) of the
medium and inversely proportional to its density. Therefore, a material that is stiff and not
dense (like bone) transmits sound fastest.
3. Two sound waves are traveling through soft tissue. Wave A has a frequency of 2 MHz,
and Wave B has a frequency of 10 MHz. Which of the following statements is true
regarding their propagation speeds?
A) Wave B travels five times faster than Wave A.
B) Wave A travels five times faster than Wave B.
C) Wave A and Wave B travel at the exact same speed.
, D) Wave B travels faster due to a shorter period.
Elaboration: The propagation speed of a sound wave is determined exclusively by the
physical properties of the medium (tissue), not by the frequency of the wave. Both waves
travel at approximately 1540 m/s in soft tissue.
4. The period of a 5 MHz ultrasound wave is most accurately expressed as:
A) 0.5 milliseconds
B) 0.2 microseconds
C) 2.0 microseconds
D) 0.02 milliseconds
Elaboration: Period ($T$) is the reciprocal of frequency ($f$). $T = ,000,000 \text{ Hz} =
0.0000002 \text{ seconds}$, which is 0.2 $\mu$s.
5. When an acoustic wave travels from a medium with a high acoustic velocity to a
medium with a low acoustic velocity, which parameter of the wave changes?
A) Frequency increases.
B) Frequency decreases.
C) Wavelength decreases.
D) Wavelength increases.
Elaboration: Frequency is determined by the sound source and remains constant when
crossing boundaries. According to $c = f \lambda$, if propagation speed ($c$) decreases and
frequency ($f$) remains constant, the wavelength ($\lambda$) must decrease.
6. What determines the initial amplitude of an ultrasound wave?
A) The acoustic impedance of the tissue.
B) The attenuation coefficient of the medium.
C) The thickness of the matching layer.
D) The electrical voltage applied to the piezoelectric crystal.
Elaboration: Initial amplitude, power, and intensity are all determined by the magnitude of
the electrical excitation voltage applied to the transducer elements by the ultrasound system
pulser.
7. A 3 dB decrease in the intensity of an ultrasound beam represents a reduction to what
fraction of the original intensity?
, A) One-tenth
B) One-third
C) One-half
D) One-quarter
Elaboration: The decibel scale is logarithmic. A change of -3 dB indicates that the intensity has
been halved. A change of -10 dB indicates a reduction to one-tenth.
8. Which of the following acoustic parameters is determined by both the sound source and
the medium?
A) Period
B) Frequency
C) Propagation speed
D) Wavelength
Elaboration: Wavelength is the only parameter determined by both the source (which
dictates frequency) and the medium (which dictates propagation speed), as defined by the
equation $\lambda = c / f$.
9. In soft tissue, the attenuation coefficient is approximately equal to:
A) The operating frequency multiplied by 2.
B) One-half of the operating frequency in MHz.
C) The acoustic impedance divided by the frequency.
D) The spatial pulse length squared.
Elaboration: In soft tissue, the attenuation coefficient is approximately $0.5 \text{
dB/cm/MHz}$. Therefore, it is estimated as half the transducer's operating frequency.
10. Which interaction of sound and tissue is primarily responsible for the echogenicity of
red blood cells?
A) Specular reflection
B) Refraction
C) Rayleigh scattering
D) Absorption
US Physics DMS 600: Diagnostic Medical Sonography
100-Question Advanced Master Bank
Section 1: Properties of Sound Waves
1. If the operating frequency of an ultrasound transducer is reduced by half, what is the
corresponding effect on the spatial pulse length (SPL), assuming the number of cycles
per pulse remains constant?
A) The SPL is reduced to one-quarter of its original value.
B) The SPL is reduced by half.
C) The SPL remains unchanged because it is determined by the damping material.
D) The SPL is doubled.
Elaboration: Spatial Pulse Length is calculated as the number of cycles multiplied by the
wavelength. Because frequency and wavelength are inversely proportional ($c = f \lambda$),
halving the frequency doubles the wavelength, thereby doubling the SPL.
2. Which of the following combinations of medium properties will result in the highest
propagation speed for an acoustic wave?
A) High density and high compressibility.
B) Low density and high stiffness.
C) High density and low stiffness.
D) Low density and high compressibility.
Elaboration: Propagation speed is directly proportional to the stiffness (bulk modulus) of the
medium and inversely proportional to its density. Therefore, a material that is stiff and not
dense (like bone) transmits sound fastest.
3. Two sound waves are traveling through soft tissue. Wave A has a frequency of 2 MHz,
and Wave B has a frequency of 10 MHz. Which of the following statements is true
regarding their propagation speeds?
A) Wave B travels five times faster than Wave A.
B) Wave A travels five times faster than Wave B.
C) Wave A and Wave B travel at the exact same speed.
, D) Wave B travels faster due to a shorter period.
Elaboration: The propagation speed of a sound wave is determined exclusively by the
physical properties of the medium (tissue), not by the frequency of the wave. Both waves
travel at approximately 1540 m/s in soft tissue.
4. The period of a 5 MHz ultrasound wave is most accurately expressed as:
A) 0.5 milliseconds
B) 0.2 microseconds
C) 2.0 microseconds
D) 0.02 milliseconds
Elaboration: Period ($T$) is the reciprocal of frequency ($f$). $T = ,000,000 \text{ Hz} =
0.0000002 \text{ seconds}$, which is 0.2 $\mu$s.
5. When an acoustic wave travels from a medium with a high acoustic velocity to a
medium with a low acoustic velocity, which parameter of the wave changes?
A) Frequency increases.
B) Frequency decreases.
C) Wavelength decreases.
D) Wavelength increases.
Elaboration: Frequency is determined by the sound source and remains constant when
crossing boundaries. According to $c = f \lambda$, if propagation speed ($c$) decreases and
frequency ($f$) remains constant, the wavelength ($\lambda$) must decrease.
6. What determines the initial amplitude of an ultrasound wave?
A) The acoustic impedance of the tissue.
B) The attenuation coefficient of the medium.
C) The thickness of the matching layer.
D) The electrical voltage applied to the piezoelectric crystal.
Elaboration: Initial amplitude, power, and intensity are all determined by the magnitude of
the electrical excitation voltage applied to the transducer elements by the ultrasound system
pulser.
7. A 3 dB decrease in the intensity of an ultrasound beam represents a reduction to what
fraction of the original intensity?
, A) One-tenth
B) One-third
C) One-half
D) One-quarter
Elaboration: The decibel scale is logarithmic. A change of -3 dB indicates that the intensity has
been halved. A change of -10 dB indicates a reduction to one-tenth.
8. Which of the following acoustic parameters is determined by both the sound source and
the medium?
A) Period
B) Frequency
C) Propagation speed
D) Wavelength
Elaboration: Wavelength is the only parameter determined by both the source (which
dictates frequency) and the medium (which dictates propagation speed), as defined by the
equation $\lambda = c / f$.
9. In soft tissue, the attenuation coefficient is approximately equal to:
A) The operating frequency multiplied by 2.
B) One-half of the operating frequency in MHz.
C) The acoustic impedance divided by the frequency.
D) The spatial pulse length squared.
Elaboration: In soft tissue, the attenuation coefficient is approximately $0.5 \text{
dB/cm/MHz}$. Therefore, it is estimated as half the transducer's operating frequency.
10. Which interaction of sound and tissue is primarily responsible for the echogenicity of
red blood cells?
A) Specular reflection
B) Refraction
C) Rayleigh scattering
D) Absorption
