VT Ultrasound Physics & Doppler Principles 2 — Questions and Answers
Question 1: What phenomenon occurs when the ultrasound beam strikes a smooth, flat interface larger than the wavelength?
- Scattering
- Specular reflection (Correct answer)
- Refraction
- Absorption
Correct answer: Specular reflection
Specular reflection occurs at large, smooth interfaces where the beam reflects at an angle equal to the angle of incidence.
Question 2: The Nyquist limit in pulsed-wave Doppler is equal to:
- The pulse repetition frequency
- One-half the pulse repetition frequency (Correct answer)
- Twice the pulse repetition frequency
- The carrier frequency
Correct answer: One-half the pulse repetition frequency
The Nyquist limit equals PRF/2; velocities exceeding this cause aliasing in pulsed-wave Doppler.
Question 3: Which parameter most directly controls the depth of penetration of an ultrasound beam?
- Amplitude
- Frequency (Correct answer)
- Frame rate
- Line density
Correct answer: Frequency
Lower frequencies penetrate deeper because they are attenuated less per centimeter of tissue.
Question 4: In continuous-wave Doppler, which limitation does NOT apply?
- Range ambiguity
- Nyquist limit (Correct answer)
- Angle dependence
- Wall filter requirement
Correct answer: Nyquist limit
CW Doppler has no PRF, so there is no Nyquist limit and it can detect very high velocities without aliasing.
Question 5: Acoustic impedance (Z) is defined as the product of:
- Frequency and wavelength
- Density and propagation speed (Correct answer)
- Amplitude and attenuation
- Power and beam area
Correct answer: Density and propagation speed
Z = ρ × c, where ρ is tissue density and c is the speed of sound in that medium.
Question 6: A color Doppler display showing flow encoded in blue away from the transducer and red toward it follows which convention?
- BART (Blue Away, Red Toward) (Correct answer)
- RABT (Red Away, Blue Toward)
- Standard angiographic convention
- Inverted Doppler mode
Correct answer: BART (Blue Away, Red Toward)
BART is the standard color Doppler convention: Blue Away, Red Toward the transducer.
Question 7: Which artifact appears as equally spaced, repeated copies of a structure deeper than the true structure?
- Side lobe artifact
- Reverberation artifact (Correct answer)
- Shadowing artifact
- Enhancement artifact
Correct answer: Reverberation artifact
Reverberation artifacts occur when sound bounces repeatedly between two strong reflectors, producing equally spaced copies.
VT Ultrasound Physics & Doppler Principles 2
What phenomenon occurs when the ultrasound beam strikes a smooth, flat interface larger than the wavelength?