ARDMS SPI Attenuation, Reflection, and Refraction 4 — Questions and Answers
Question 1: Acoustic shadowing distal to a gallstone is primarily due to:
- High attenuation and reflection by the calcified stone (Correct answer)
- Low propagation speed in the stone
- Refraction at the stone's curved surface
- Constructive interference behind the stone
Correct answer: High attenuation and reflection by the calcified stone
Gallstones strongly reflect and absorb sound, leaving a shadow of reduced echo amplitude posterior to the stone.
Question 2: Which property of a medium directly determines whether refraction will occur at an oblique interface?
- Propagation speed (Correct answer)
- Acoustic impedance
- Attenuation coefficient
- Frequency absorption rate
Correct answer: Propagation speed
Refraction depends on differing propagation speeds in adjacent media, not on their impedances.
Question 3: The average propagation speed of sound in soft tissue used by ultrasound systems is:
- 1540 m/s (Correct answer)
- 1480 m/s
- 330 m/s
- 1600 m/s
Correct answer: 1540 m/s
Ultrasound machines assume a propagation speed of 1540 m/s in soft tissue for depth calculations.
Question 4: Non-specular (diffuse) reflectors differ from specular reflectors in that they:
- Scatter sound in many directions regardless of beam angle (Correct answer)
- Only reflect when struck perpendicularly
- Produce echoes proportional to acoustic impedance alone
- Require higher frequency to produce echoes
Correct answer: Scatter sound in many directions regardless of beam angle
Non-specular (diffuse) reflectors have irregular or small surfaces that scatter sound in all directions, making them angle-independent.
Question 5: Which factor does NOT directly affect the intensity reflection coefficient at a tissue interface?
- Transducer frequency (Correct answer)
- Acoustic impedance of medium 1
- Acoustic impedance of medium 2
- Angle of incidence
Correct answer: Transducer frequency
At normal incidence, the reflection coefficient depends only on the two media's acoustic impedances, not on frequency.
Question 6: Increasing the depth of imaging requires using a lower frequency primarily because:
- Lower frequencies undergo less attenuation per centimeter (Correct answer)
- Lower frequencies have higher propagation speed
- Lower frequencies produce less refraction
- Lower frequencies increase acoustic impedance mismatch
Correct answer: Lower frequencies undergo less attenuation per centimeter
Attenuation per centimeter decreases with lower frequency, allowing sound to penetrate deeper into tissue.
Question 7: Which of the following best describes the transmission coefficient when sound passes from one medium to another?
- It equals 1 minus the reflection coefficient (Correct answer)
- It equals the product of the two impedances
- It is always less than the reflection coefficient
- It depends on frequency but not impedance
Correct answer: It equals 1 minus the reflection coefficient
Conservation of energy requires that the transmission coefficient T = 1 − R, where R is the reflection coefficient.
ARDMS SPI Attenuation, Reflection, and Refraction 4
Acoustic shadowing distal to a gallstone is primarily due to: