Doppler spectral characterization of flow disturbances in the carotid with the Doppler probe at right angles to the vessel axis.

This paper reports on a new method intended to detect early flow disturbances generated by small lesions, using conventional clinical instrumentation. In vitro experiments on models of stenotic vessels are presented which prove that ultrasound Doppler, with the beam directed at right angles to the vessel axis can detect vortices and other flow disturbances caused by wall irregularities. These disturbances characterized by small velocity components first toward and then away from the transducer correlate with the spectrum of vortices caused by small artificial lesions. We found these disturbances in flow to be too small to cause detectable broadening in the Doppler spectrum acquired in the traditional way (i.e. with the beam at an angle less than 90 degrees). The detected flow disturbances were found to depend on the surface roughness, the profile of the obstructive lesion and the narrowing of the vessel. Similar flow disturbances to those detected in vitro were demonstrated in vivo for this new beam orientation in regions of the carotid, such as the bulb and the beginning of the common carotid, where vortex-like flows are expected.