The minimum number of samples required to avoid aliasing; Doppler shift frequency above which aliasing occurs is known as what?

• A. Nyquist limit
• B. Sampling rate
• C. Cutoff frequency
• D. Resolution limit

Answer: (A)

Nyquist limit is the threshold that sets the maximum Doppler frequency you can measure without aliasing. In Doppler ultrasound, signals are sampled at a given PRF, so any Doppler shift must be less than half of that sampling rate to be reconstructed accurately. This boundary—half the sampling rate—is the Nyquist limit. If the Doppler frequency exceeds it, aliasing occurs, causing velocity values to wrap around and appear incorrect. The other terms don’t denote this boundary: the sampling rate is the actual sampling pace, a cutoff frequency relates to filters, and the resolution limit concerns how finely you can distinguish details, not the aliasing threshold.