Ways To Eliminate Aliasing

Aliasing is a phenomenon that is seen on pulse wave doppler when the high flow velocities generate doppler shifts exceeding the Nyquist limit. There are a number of ways aliasing can be eliminated:

Using a low frequency transducer

As is discussed in previous questions, the doppler shift frequency (Fd) is directly related to the transducer frequency (F0). By doing so, the doppler shift reduces and could eliminate aliasing.

Reducing the depth

Changing the imaging to a shallower depth decreases the pulse repetition period (PRP). The PRP is inversely related to the pulse repetition frequency (PRF), which in turn is directly related to the Nyquist limit. In other words, the PRF is increased -> increased Nyquist limit -> reduced aliasing

Using continuous wave imaging

This is the better option when compared to pulse wave doppler at higher velocities. This is because there are 2 crystals involved in CW doppler, resulting in the absence of ‘listening time’.

Increase the angle of the probe

Remember the angle Ø? Increasing the angle of the probe can decrease the doppler shift, and eliminates aliasing.

Change colour and velocity scale

This may help.