Which Doppler mode does not exhibit aliasing?

Which Doppler mode does not exhibit aliasing?

• A. Pulsed-wave
• B. Color Doppler
• C. Continuous-wave
• D. Power Doppler

Answer: (C)

Aliasing happens when the Doppler frequency is sampled at a finite rate, the pulse repetition frequency, so high velocities can wrap around and appear as lower ones. In pulsed-wave and color Doppler, velocity information is tied to this PRF sampling, so when the true flow velocity exceeds half the PRF (the Nyquist limit), aliasing appears on the display. Continuous-wave Doppler, on the other hand, transmits and receives continuously and does not rely on a discrete PRF for sampling velocity. Because there’s no range-gated sampling to wrap around, high velocities can be measured without aliasing. Power Doppler isn’t about velocity at all—it measures signal strength rather than Doppler frequency—so aliasing tied to velocity isn’t a factor there, though other artifacts can occur. Therefore, continuous-wave Doppler is the mode that does not exhibit aliasing.

Aliasing happens when the Doppler frequency is sampled at a finite rate, the pulse repetition frequency, so high velocities can wrap around and appear as lower ones. In pulsed-wave and color Doppler, velocity information is tied to this PRF sampling, so when the true flow velocity exceeds half the PRF (the Nyquist limit), aliasing appears on the display. Continuous-wave Doppler, on the other hand, transmits and receives continuously and does not rely on a discrete PRF for sampling velocity. Because there’s no range-gated sampling to wrap around, high velocities can be measured without aliasing. Power Doppler isn’t about velocity at all—it measures signal strength rather than Doppler frequency—so aliasing tied to velocity isn’t a factor there, though other artifacts can occur. Therefore, continuous-wave Doppler is the mode that does not exhibit aliasing.