Diagram shows a normal arterial spectrum obtained with Doppler US, the parameters that define it, and the general terms used to describe it. PSV = peak systolic velocity, EDV = end-diastolic velocity.
The spectral window is the clear black zone between the spectral line and the baseline. Widening of the spectral line and filling of the spectral window is called spectral broadening. Spectral broadening is normally seen in the presence of high flow velocity, at the branching of a vessel, or in small-diameter vessels.






http://radiographics.rsna.org/content/28/3/691.full