In Doppler sonography, aliasing occurs when the maximum Doppler shift exceeds which limit?

In Doppler sonography, aliasing occurs when the maximum Doppler shift exceeds which limit?

• A. Doppler shift
• B. Velocity scale
• C. Sampling frequency
• D. Nyquist limit

Answer: (D)

Aliasing in Doppler sonography happens when the Doppler frequency shift is larger than what the sampling rate can unambiguously represent. The limit that governs this is the Nyquist limit, which equals half the sampling frequency (the pulse repetition frequency). When the Doppler shift exceeds this limit, the signal folds back and appears as a different velocity or flow direction. So the unaliasable boundary is the Nyquist limit.

Aliasing in Doppler sonography happens when the Doppler frequency shift is larger than what the sampling rate can unambiguously represent. The limit that governs this is the Nyquist limit, which equals half the sampling frequency (the pulse repetition frequency). When the Doppler shift exceeds this limit, the signal folds back and appears as a different velocity or flow direction. So the unaliasable boundary is the Nyquist limit.