Color Doppler Aliasing - Video Lesson

Hey, everybody. Welcome to today's lesson on Doppler ultrasound. This lesson focuses on color Doppler, in particular, color Doppler aliasing. Aliasing occurs when the Doppler shift exceeds the Nyquist limit, leading to inaccurate color representation of flow velocities. Remember, the Nyquist limit can be thought of as the speed limit. It is the highest Doppler velocity that can be measured without aliasing. If the Doppler shift goes over the speed limit, aliasing occurs. The Nyquist limit is equal to the pulse repetition frequency, the PRF, divided by two. So if the PRF is eight Hertz, the Nyquist limit is four Hertz. Aliasing in color Doppler manifests as an abrupt color reversal on the color Doppler map. In other words, aliasing appears as a sudden and unnatural color change within a blood vessel. Instead of a smooth transition between colors that represent increasing or decreasing velocity, you see an abrupt flip between opposite colors on the color map.