A method used to allow measurement of high velocities with pulsed Doppler while reducing aliasing.

A method used to allow measurement of high velocities with pulsed Doppler while reducing aliasing.

• A. Beat frequency
• B. Power Doppler
• C. Spectral Doppler
• D. High-PRF Doppler

Answer: (D)

Aliasing in pulsed Doppler happens when the Doppler shift exceeds half the pulse repetition frequency, the Nyquist limit. When flow speeds are very high, the measured frequency wraps around and can appear as a lower velocity or reverse direction. Increasing the pulse repetition frequency raises that Nyquist limit, letting you measure larger Doppler shifts before aliasing occurs. High-PRF Doppler uses a higher PRF to extend the measurable velocity range and reduce aliasing, which is exactly how you can assess fast flow without it wrapping. The trade-off is that raising PRF can narrow the depth range due to range ambiguity, but for evaluating high-velocity flow, this approach is the most effective. Beat frequency relates to mixing signals and isn’t the method to control aliasing in pulsed Doppler; Power Doppler shows flow strength but not velocity and doesn’t address aliasing; spectral Doppler shows velocities but will alias if PRF isn’t high enough.

Aliasing in pulsed Doppler happens when the Doppler shift exceeds half the pulse repetition frequency, the Nyquist limit. When flow speeds are very high, the measured frequency wraps around and can appear as a lower velocity or reverse direction. Increasing the pulse repetition frequency raises that Nyquist limit, letting you measure larger Doppler shifts before aliasing occurs. High-PRF Doppler uses a higher PRF to extend the measurable velocity range and reduce aliasing, which is exactly how you can assess fast flow without it wrapping. The trade-off is that raising PRF can narrow the depth range due to range ambiguity, but for evaluating high-velocity flow, this approach is the most effective. Beat frequency relates to mixing signals and isn’t the method to control aliasing in pulsed Doppler; Power Doppler shows flow strength but not velocity and doesn’t address aliasing; spectral Doppler shows velocities but will alias if PRF isn’t high enough.