False statement about Aliasing:

Correct answer: b) Aliasing occurs when the velocity being interrogated is below the Nyquist limit
Aliasing occurs when the velocity being interrogated by Doppler echocardiography is above the Nyquist limit.

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