Which parameter controls the Nyquist limit in Doppler ultrasound?

Which parameter controls the Nyquist limit in Doppler ultrasound?

• A. Doppler angle
• B. Pulse repetition frequency
• C. Depth
• D. Sample volume length

Answer: (B)

The Nyquist limit in Doppler ultrasound is set by how often you sample the signal, which is the pulse repetition frequency (PRF). In Doppler, the Doppler shift must be less than half of the PRF (PRF/2) to be measured unambiguously. If the shift exceeds that, aliasing occurs. So increasing PRF raises the Nyquist limit and allows higher velocities to be measured without aliasing, though it can limit maximum imaging depth due to range ambiguity. The Doppler angle affects how velocity translates to a frequency shift, but it doesn’t change the Nyquist limit itself. Depth and sample volume length influence depth range and resolution, not the sampling limit that governs aliasing.

The Nyquist limit in Doppler ultrasound is set by how often you sample the signal, which is the pulse repetition frequency (PRF). In Doppler, the Doppler shift must be less than half of the PRF (PRF/2) to be measured unambiguously. If the shift exceeds that, aliasing occurs. So increasing PRF raises the Nyquist limit and allows higher velocities to be measured without aliasing, though it can limit maximum imaging depth due to range ambiguity. The Doppler angle affects how velocity translates to a frequency shift, but it doesn’t change the Nyquist limit itself. Depth and sample volume length influence depth range and resolution, not the sampling limit that governs aliasing.