What color Doppler artifact occurs when you cannot raise the PRF beyond twice the Doppler frequency shift?

What color Doppler artifact occurs when you cannot raise the PRF beyond twice the Doppler frequency shift?

• A. Range ambiguity
• B. Aliasing
• C. Overestimation of flow velocity
• D. Overestimation of Doppler frequency shift

Answer: (B)

Color Doppler sampling is limited by the Nyquist limit, which is half the pulse repetition frequency (PRF). When the Doppler frequency shift you’re trying to measure is larger than this limit, the displayed color wraps around and appears on the opposite end of the scale or changes direction incorrectly—that’s aliasing. If you can’t raise the PRF beyond twice the Doppler shift, you can’t increase the Nyquist limit enough to cover the true shift, so aliasing inevitably shows up. This artifact is different from range-related issues (which come from sampling depth) and from mere overestimation tendencies, which aren’t the characteristic wraparound seen with aliasing.

Color Doppler sampling is limited by the Nyquist limit, which is half the pulse repetition frequency (PRF). When the Doppler frequency shift you’re trying to measure is larger than this limit, the displayed color wraps around and appears on the opposite end of the scale or changes direction incorrectly—that’s aliasing. If you can’t raise the PRF beyond twice the Doppler shift, you can’t increase the Nyquist limit enough to cover the true shift, so aliasing inevitably shows up. This artifact is different from range-related issues (which come from sampling depth) and from mere overestimation tendencies, which aren’t the characteristic wraparound seen with aliasing.