Aliasing is a potential problem in pulsed-wave Doppler because of:

Aliasing is a potential problem in pulsed-wave Doppler because of:

• A. The use of high pulse repetition frequencies
• B. The Doppler signal is sampled rather than recorded continuously
• C. Dynamic focusing
• D. The motion of the interface perpendicular to ultrasound wave propagation

Answer: (B)

Aliasing in pulsed-wave Doppler comes from how the signal is captured. The Doppler signal is sampled at discrete times defined by the pulse repetition frequency, not recorded as a continuous wave. Because of this sampling, the highest Doppler frequency that can be unambiguously measured is half the sampling rate (the Nyquist limit). If the actual Doppler shift from blood flow exceeds that limit, it folds back and appears as a lower frequency or even the opposite direction, creating aliasing in the spectrum. This is why the sampling nature is the root cause. Increasing the PRF or using velocity scales appropriately helps prevent aliasing, and switching to continuous-wave Doppler avoids this particular sampling limitation. Dynamic focusing or motion perpendicular to the beam do not cause aliasing themselves.

Aliasing in pulsed-wave Doppler comes from how the signal is captured. The Doppler signal is sampled at discrete times defined by the pulse repetition frequency, not recorded as a continuous wave. Because of this sampling, the highest Doppler frequency that can be unambiguously measured is half the sampling rate (the Nyquist limit). If the actual Doppler shift from blood flow exceeds that limit, it folds back and appears as a lower frequency or even the opposite direction, creating aliasing in the spectrum. This is why the sampling nature is the root cause. Increasing the PRF or using velocity scales appropriately helps prevent aliasing, and switching to continuous-wave Doppler avoids this particular sampling limitation. Dynamic focusing or motion perpendicular to the beam do not cause aliasing themselves.