ARDMS SPI Acoustic Waves and Properties 3 — Questions and Answers
Question 1: Which tissue type has the highest acoustic propagation speed?
- Fat
- Soft tissue
- Bone (Correct answer)
- Air
Correct answer: Bone
Bone has the highest stiffness among listed tissues, giving it the greatest propagation speed (~3500 m/s).
Question 2: Specular reflection occurs when sound strikes a boundary that is:
- Smaller than the wavelength
- Rough relative to the wavelength
- Large and smooth relative to the wavelength (Correct answer)
- Angled at 90° to the beam
Correct answer: Large and smooth relative to the wavelength
Specular reflectors are large, flat, smooth surfaces that reflect sound at an angle equal to the incident angle, like a mirror.
Question 3: Attenuation of ultrasound in soft tissue is approximately:
- 0.5 dB/cm/MHz (Correct answer)
- 5 dB/cm/MHz
- 0.05 dB/cm/MHz
- 50 dB/cm/MHz
Correct answer: 0.5 dB/cm/MHz
The standard approximation for attenuation in soft tissue is 0.5 dB/cm/MHz, used clinically for TGC calculations.
Question 4: Scattering of ultrasound is most likely to occur when the reflecting structure is:
- Much larger than the wavelength
- Similar in size or smaller than the wavelength (Correct answer)
- A perfect flat surface
- Located at the transducer face
Correct answer: Similar in size or smaller than the wavelength
Non-specular (diffuse) scattering occurs when reflectors are small relative to wavelength, producing omnidirectional echoes used in gray-scale imaging.
Question 5: When sound passes from a medium with low acoustic impedance to one with high acoustic impedance, the reflected wave will have:
- A phase shift of 180° (Correct answer)
- No phase change
- Doubled amplitude
- Reduced frequency
Correct answer: A phase shift of 180°
Reflection at an interface where impedance increases causes a 180° phase reversal (pressure inversion) of the reflected wave.
Question 6: The decibel (dB) scale is used in ultrasound because:
- It simplifies multiplication of intensities into addition (Correct answer)
- It makes calculations linear
- It directly measures wavelength
- It eliminates the need for gain adjustment
Correct answer: It simplifies multiplication of intensities into addition
The logarithmic dB scale converts large multiplicative intensity ratios into manageable additive numbers, matching human perception of loudness.
Question 7: Which of the following is NOT a mechanism of ultrasound attenuation in tissue?
- Absorption
- Reflection
- Scattering
- Refraction (Correct answer)
Correct answer: Refraction
Refraction redirects the beam but does not remove energy from it, so it is not an attenuation mechanism; absorption, reflection, and scattering all reduce beam intensity.
ARDMS SPI Acoustic Waves and Properties 3
Which tissue type has the highest acoustic propagation speed?