ARDMS Echo Doppler Principles and Applications 1 — Questions and Answers
Question 1: What is the Nyquist limit in pulsed wave Doppler echocardiography?
- Half the pulse repetition frequency (Correct answer)
- The pulse repetition frequency
- Twice the pulse repetition frequency
- The transducer frequency
Correct answer: Half the pulse repetition frequency
The Nyquist limit equals half the pulse repetition frequency (PRF); exceeding it causes aliasing in pulsed wave Doppler.
Question 2: Which Doppler modality is best suited for measuring high-velocity jets such as severe aortic stenosis?
- Continuous wave Doppler (Correct answer)
- Pulsed wave Doppler
- Color flow Doppler
- Power Doppler
Correct answer: Continuous wave Doppler
Continuous wave Doppler has no PRF limitation and can accurately measure high-velocity jets without aliasing.
Question 3: What effect does increasing the angle of insonation (θ) beyond 20° have on Doppler velocity measurements?
- Underestimates true velocity (Correct answer)
- Overestimates true velocity
- No effect on velocity
- Improves spatial resolution
Correct answer: Underestimates true velocity
The Doppler equation uses cosine θ; as θ increases beyond 20°, cosine decreases, causing underestimation of true blood flow velocity.
Question 4: In color flow Doppler, what does aliasing (color reversal to the opposite color) indicate?
- Velocities exceeding the Nyquist limit (Correct answer)
- Turbulent flow only
- Backscatter artifact
- Gain set too low
Correct answer: Velocities exceeding the Nyquist limit
Color aliasing occurs when detected velocity exceeds the Nyquist limit, causing the display to wrap to the opposite color.
Question 5: Which Doppler technique allows simultaneous visualization of flow direction and velocity across a 2D image?
- Color flow Doppler (Correct answer)
- Pulsed wave Doppler
- Continuous wave Doppler
- Tissue Doppler imaging
Correct answer: Color flow Doppler
Color flow Doppler maps mean blood flow velocities across a 2D sector, color-coding direction and relative velocity.
Question 6: What is the primary advantage of tissue Doppler imaging (TDI) over conventional Doppler in diastolic assessment?
- It measures myocardial wall motion velocity and is less preload dependent (Correct answer)
- It measures blood flow velocity more accurately
- It is not affected by angle of insonation
- It detects higher velocities without aliasing
Correct answer: It measures myocardial wall motion velocity and is less preload dependent
TDI measures low-velocity, high-amplitude myocardial motion and the resulting e' velocity is relatively preload independent, useful for diastolic assessment.
ARDMS Echo Doppler Principles and Applications 1
What is the Nyquist limit in pulsed wave Doppler echocardiography?