What is Aliasing in Doppler Echo?

What is Aliasing in Doppler Echo?

Aliasing occurs when the velocity being interrogated by Doppler echocardiography is above the Nyquist limit.

Continuous wave Doppler recording showing aortic regurgitation jet above the baseline with a cut off at the upper end and a wrap around seen below the baseline. Here aliasing is seen because the velocity limit of the Doppler has been set just above 200 cm/second while AR jet velocity is higher than that.

The tracing can be depicted upwards to its full extend by adjusting the velocity limit or by adjusting the baseline downwards. If the velocity range is lowered much below 200 cm/second, AR jet will appear above and below the base line in a similar fashion as is seen above the baseline now. This is because a second wrap around occurs at the lower end below the baseline. It is in that situation that identifying the actual direction of the jet becomes difficult.

Dense jet seen below the baseline is the forward aortic flow. The peak forward gradient is measured as 20 mm Hg, which does not indicate significant associated aortic stenosis.