Name two common strategies to mitigate Doppler aliasing in PW Doppler.

• A. Increase PRF (adjust depth/sector), or lower the baseline and/or use alternative modes like CW Doppler
• B. Decrease PRF and increase baseline
• C. Increase gain and reduce sector width
• D. Use color Doppler only

Answer: (A)

Doppler aliasing happens when the velocity being measured exceeds the Nyquist limit, which is half the pulse repetition frequency (PRF). To reduce or avoid aliasing in pulsed-wave Doppler, two common strategies work well: raise the PRF and move away from aliasing by using a mode that doesn’t have a range-specific sampling.

Raising the PRF increases the Nyquist limit, so faster flows won’t wrap around as easily. You can achieve this by choosing a shallower depth, narrowing the sector, or selecting a higher PRF setting. If depth or sector constraints allow, this is one of the most effective fixes.

Lowering the baseline or shifting the display can help situationally by reordering where the aliased wrap appears on the velocity display, sometimes making it easier to interpret within the region of interest. It’s a display adjustment rather than a true change to the unambiguous velocity range, so it’s a useful quick trick but not as robust as increasing PRF.

Switching to continuous-wave Doppler eliminates aliasing because it samples along all ranges continuously (no range-gated sampling), though you sacrifice range resolution and localization.

Options that don’t affect the Nyquist limit—like increasing gain or changing sector width without altering PRF—don’t prevent aliasing. Using color Doppler alone doesn’t remove the fundamental range-velocity limitation of PW Doppler.