Aliasing and Nyquist Limit in Doppler Echo

Aliasing is a phenomenon in pulsed Doppler echocardiography in which when the velocity is beyond a particular limit known as the Nyquist limit, the direction of flow is depicted as opposite to that of the actual one. Nyquist limit is half the pulse repetition frequency of the ultrasound signal emitted by the Doppler transducer. Aliasing does not occur in continuous wave Doppler as the transmission of Doppler beam is continuous and not in pulses.