In vitro Doppler detection of axisymmetric stenoses from transverse velocity measurements

Results are presented on Doppler flow measurements distal to models of arterial stenosis under steady and pulsatile flow conditions. The models simulate mild to moderate stenoses. Emphasis is placed on flow structure determination (vortex shedding or coherent eddies) which might be the distinguishing characteristic of a mild stenosis (less than or equal to 50%). A new approach is taken by making the measurements with the ultrasonic beam normal to the axial flow direction. The transverse velocity measurements avoid detecting the superposed axial flow component so that flow structure can be determined, and also provide clinical advantages of the ease of localization. A pulsed RF directional Doppler system is used together with high resolution temporal autoregressive spectral analysis. Vortex shedding and coherent structures are detected under steady and pulsatile flow conditions. The influence of the frequency parameter on the flow pattern is also studied.