ARDMS SPI Acoustic Waves and Properties 4 β Questions and Answers
Question 1: Snell's Law in ultrasound describes the relationship between:
- Frequency and depth
- Incident and refracted beam angles at a tissue boundary (Correct answer)
- Intensity and attenuation
- Pulse duration and bandwidth
Correct answer: Incident and refracted beam angles at a tissue boundary
Snell's Law states that the sine of the angle of incidence to the sine of the angle of refraction equals the ratio of propagation speeds in the two media.
Question 2: What is the approximate average propagation speed of ultrasound assumed by diagnostic scanners in soft tissue?
- 1000 m/s
- 1540 m/s (Correct answer)
- 3500 m/s
- 331 m/s
Correct answer: 1540 m/s
Diagnostic ultrasound machines assume 1540 m/s (1.54 mm/Β΅s) as the average soft-tissue propagation speed for depth calculation.
Question 3: The reflection coefficient at a tissue interface is primarily determined by the difference in:
- Frequencies of the incident waves
- Acoustic impedances of the two media (Correct answer)
- Pulse repetition frequencies
- Transducer depths
Correct answer: Acoustic impedances of the two media
The intensity reflection coefficient depends on (Z2 β Z1)Β² / (Z2 + Z1)Β², where Z1 and Z2 are the acoustic impedances of the two media.
Question 4: Increasing the amplitude of an ultrasound wave will directly increase its:
- Frequency
- Propagation speed
- Acoustic power and intensity (Correct answer)
- Wavelength
Correct answer: Acoustic power and intensity
Amplitude is proportional to pressure variation; acoustic intensity is proportional to amplitude squared, so larger amplitude means greater power and intensity.
Question 5: A sound wave with frequency of 5 MHz traveling through soft tissue (c = 1540 m/s) has a wavelength of approximately:
- 0.31 mm (Correct answer)
- 3.1 mm
- 0.031 mm
- 31 mm
Correct answer: 0.31 mm
Ξ» = c / f = 1540 m/s Γ· 5,000,000 Hz = 0.000308 m β 0.31 mm.
Question 6: What happens to the transmission of sound energy when two tissues have identical acoustic impedances?
- All energy is reflected
- No energy is transmitted
- There is no reflection; all energy is transmitted (Correct answer)
- Half the energy is reflected
Correct answer: There is no reflection; all energy is transmitted
When Z1 = Z2, the impedance mismatch is zero, producing no reflection and allowing complete transmission of the ultrasound beam.
Question 7: Which of the following best defines the acoustic property 'stiffness' of a medium in the context of sound propagation?
- The medium's resistance to being compressed (Correct answer)
- The medium's density per unit volume
- The wavelength of sound within the medium
- The attenuation coefficient of the medium
Correct answer: The medium's resistance to being compressed
Stiffness (bulk modulus) is the medium's resistance to compression; stiffer media transmit sound faster because they restore disturbed particles more quickly.
ARDMS SPI Acoustic Waves and Properties 4
Snell's Law in ultrasound describes the relationship between: