Analysis of ultrasonic Doppler velocity data obtained in models of stenosed carotid bifurcations with irregular lesion surface.

In this study properties are concerned of ultrasonic Doppler spectra recorded distal to an irregularity localised in the internal carotid artery of a true-to-scale elastic model of a severely stenosed carotid bifurcation. Four models differing in irregularity were obtained by melting graded holes in the original wax cast, about 5-7 mm distal to the bifurcation. Velocity data were collected using an HP Sonos 2500 ultrasonograph working in pulsed Doppler mode. The observed effect of the irregularity with respect to the smooth wall model consisted in: (1) presence of a reduced flow zone 15 mm distal to the severe irregularity situated at the outer wall of the model in the ICA branch; (2) presence of a recirculation zone 15 mm distal to the severe irregularity situated at the inner wall of this model; (3) negative values of the measure of symmetry of the Doppler spectrum and (4) decreased values of relative width of Doppler spectra obtained 25 mm distal to the bifurcation in models with severe irregularity. The alterations of flow distribution and Doppler spectra depend on the geometry of the model under investigation and this study provides an indication as to what phenomena can happen in a model of stenosed carotid bifurcation with irregular lesion surface and how these phenomena may affect the ultrasonic Doppler spectra. Such information could be used in the evaluation of the risk of cerebral embolism.