Aliasing occurs when the Doppler signal frequency exceeds which fraction of PRF?

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Multiple Choice

Aliasing occurs when the Doppler signal frequency exceeds which fraction of PRF?

Explanation:
Aliasing in pulsed Doppler arises because the signal is sampled once every pulse repetition frequency. The highest Doppler frequency that can be measured without ambiguity is one-half of the PRF (the Nyquist limit). When the Doppler frequency shift exceeds PRF divided by 2, it folds back into the observable range and appears as a lower, misleading frequency or as a wrap-around on the spectrum. That’s why the correct threshold is one-half of PRF. Context helps: the PRF is tied to depth (PRF = c / (2 depth) in ultrasound), so deeper measurements lower the PRF and raise the chance of aliasing. To reduce aliasing, you can increase PRF (by imaging at shallower depths or using a higher PRF setting, if available), increase the display scale to accommodate higher velocities, or use continuous-wave Doppler or other techniques that avoid range sampling.

Aliasing in pulsed Doppler arises because the signal is sampled once every pulse repetition frequency. The highest Doppler frequency that can be measured without ambiguity is one-half of the PRF (the Nyquist limit). When the Doppler frequency shift exceeds PRF divided by 2, it folds back into the observable range and appears as a lower, misleading frequency or as a wrap-around on the spectrum. That’s why the correct threshold is one-half of PRF.

Context helps: the PRF is tied to depth (PRF = c / (2 depth) in ultrasound), so deeper measurements lower the PRF and raise the chance of aliasing. To reduce aliasing, you can increase PRF (by imaging at shallower depths or using a higher PRF setting, if available), increase the display scale to accommodate higher velocities, or use continuous-wave Doppler or other techniques that avoid range sampling.

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