Fig. 1From: Settings and artefacts relevant for Doppler ultrasound in large vessel vasculitisThe insonation angle is the angle between the path of the Doppler pulses and the direction of flow in the vessel as indicated by the orientation of the Doppler box. When this angle is 90° (top), there will be no frequency shift because cos(90°) = 0. With angle correction in this carotid artery more of the flow becomes detectable (bottom)Back to article page