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.
ARDMS SPI Attenuation, Reflection, and Refraction 2
Which tissue type has the highest attenuation coefficient at a given frequency?