The Nyquist limit is determined by which factor?

The Nyquist limit is determined by which factor?

• A. Depth
• B. Sample volume length
• C. PRF
• D. Pulse duration

Answer: (C)

The Nyquist limit comes from how often the signal is sampled. In Doppler ultrasound, the sampling rate is the pulse repetition frequency (PRF), so the maximum Doppler shift that can be measured without aliasing is half of that, i.e., Nyquist limit = PRF/2. That makes PRF the determining factor. Depth can change PRF (deeper imaging lowers PRF because echoes take longer to return), so it can indirectly affect the Nyquist limit, but the fundamental determinant is PRF. The other factors listed don’t set the Nyquist limit themselves; they influence depth, timing, or resolution in other ways.

The Nyquist limit comes from how often the signal is sampled. In Doppler ultrasound, the sampling rate is the pulse repetition frequency (PRF), so the maximum Doppler shift that can be measured without aliasing is half of that, i.e., Nyquist limit = PRF/2. That makes PRF the determining factor. Depth can change PRF (deeper imaging lowers PRF because echoes take longer to return), so it can indirectly affect the Nyquist limit, but the fundamental determinant is PRF. The other factors listed don’t set the Nyquist limit themselves; they influence depth, timing, or resolution in other ways.