Which parameter is directly associated with expanding the velocity range measurable without aliasing in pulsed Doppler?

Which parameter is directly associated with expanding the velocity range measurable without aliasing in pulsed Doppler?

• A. Depth
• B. Frame rate
• C. PRF increase
• D. Gain

Answer: (C)

Aliasing in pulsed Doppler is all about how often you sample the Doppler signal. The sampling rate is the pulse repetition frequency (PRF). Because you sample at discrete times, the highest Doppler frequency you can unambiguously measure is half of the PRF (the Nyquist limit). Since the Doppler shift fD is proportional to velocity, the maximum unaliased velocity grows with PRF. In formula terms, fD = 2 f0 v cosθ / c, so keeping |fD| ≤ PRF/2 gives v_max ≈ (c PRF)/(4 f0 cosθ). So increasing PRF directly expands the velocity range you can measure without aliasing. Keep in mind that raising PRF can reduce the maximum depth you can sample unambiguously, due to range ambiguity, but it doesn’t change the basic fact that aliasing is tied to the PRF. Depth, gain, and display frame rate do not set this unambiguous velocity limit.

Aliasing in pulsed Doppler is all about how often you sample the Doppler signal. The sampling rate is the pulse repetition frequency (PRF). Because you sample at discrete times, the highest Doppler frequency you can unambiguously measure is half of the PRF (the Nyquist limit). Since the Doppler shift fD is proportional to velocity, the maximum unaliased velocity grows with PRF. In formula terms, fD = 2 f0 v cosθ / c, so keeping |fD| ≤ PRF/2 gives v_max ≈ (c PRF)/(4 f0 cosθ). So increasing PRF directly expands the velocity range you can measure without aliasing. Keep in mind that raising PRF can reduce the maximum depth you can sample unambiguously, due to range ambiguity, but it doesn’t change the basic fact that aliasing is tied to the PRF. Depth, gain, and display frame rate do not set this unambiguous velocity limit.