The peak systolic velocity is measured in the artery above the stenosis, where there is no or minimal disease. 

Flow waveforms in healthy arteries exhibit pulsatile flow with reverse flow in late systole – triphasic or biphasic flowase and at the point of maximum velocity increase.

The most common threshold used to describe a haemodynamically significant stenosis is a 50% reduction in diameter. PSV ratios for this degree of stenosis have been reported from 1.8 to 2.5 in a range of studies for aorto-iliac and femoropopliteal disease, although a ratio of 2.0 is most commonly reported and used.