ARDMS SPI Attenuation, Reflection, and Refraction 2 — Questions and Answers
Question 1: Which tissue type has the highest attenuation coefficient at a given frequency?
- Bone (Correct answer)
- Fat
- Blood
- Liver
Correct answer: Bone
Bone has the highest attenuation coefficient among soft tissues and calcified structures due to its density and composition.
Question 2: When a sound beam travels from muscle into fat, which phenomenon occurs because fat has a lower propagation speed?
- Refraction (Correct answer)
- Specular reflection
- Absorption
- Scattering
Correct answer: Refraction
Refraction occurs when sound crosses an interface at an oblique angle between media with different propagation speeds, causing the beam to bend.
Question 3: What is the half-value layer (HVL) in ultrasound attenuation?
- The depth at which intensity is reduced by 50% (Correct answer)
- The frequency at which attenuation doubles
- The layer of tissue that reflects half the beam
- The transducer depth at half-power output
Correct answer: The depth at which intensity is reduced by 50%
The half-value layer is the tissue depth at which the beam's intensity is reduced to half its original value.
Question 4: A specular reflector produces a strong echo only when:
- The beam strikes the surface perpendicularly (Correct answer)
- The surface is smaller than the wavelength
- The medium has low acoustic impedance
- The frequency is below 1 MHz
Correct answer: The beam strikes the surface perpendicularly
Specular reflectors return maximum echo amplitude when the beam strikes perpendicular (90°) to the smooth, large surface.
Question 5: How does increasing ultrasound frequency affect attenuation in soft tissue?
- Attenuation increases (Correct answer)
- Attenuation decreases
- Attenuation is unaffected
- Attenuation first decreases then increases
Correct answer: Attenuation increases
Attenuation increases with frequency because higher-frequency sound waves are more readily absorbed and scattered by tissue.
Question 6: Which formula correctly relates the attenuation in dB for soft tissue?
- Attenuation (dB) ≈ 0.5 × frequency (MHz) × depth (cm) (Correct answer)
- Attenuation (dB) ≈ 2 × frequency (MHz) × depth (cm)
- Attenuation (dB) ≈ 0.1 × frequency (MHz) × depth (cm)
- Attenuation (dB) ≈ 1 × frequency (MHz) × depth (cm)
Correct answer: Attenuation (dB) ≈ 0.5 × frequency (MHz) × depth (cm)
The standard approximation is 0.5 dB/cm/MHz for soft tissue, so total attenuation = 0.5 × frequency × depth.
Question 7: Rayleigh scattering is characterized by scatterers that are:
- Much smaller than the wavelength (Correct answer)
- Much larger than the wavelength
- Equal in size to the wavelength
- Made of bone or calcified tissue only
Correct answer: Much smaller than the wavelength
Rayleigh scattering occurs when scatterers (e.g., red blood cells) are much smaller than the ultrasound wavelength, scattering energy in all directions.
