Fig. 4
From: Settings and artefacts relevant for Doppler ultrasound in large vessel vasculitis
Adjustment of pulse repetition frequency (PRF) results in simultaneous adjustment of wall filters. Left: With a low PRF the wall filters do not remove noise from the moving vessel wall as in this carotid artery (PRF 0.5 KHz). Right: When a higher PRF is selected the wall filters will eliminate the noise from the moving vessel wall and only flow inside the vessel and the correct direction of flow will be shown (PRF 3.5 KHz)