The effect of erythrocyte aggregation and flow disturbance on ultrasonic Doppler power.

摘要

The research contained in this thesis was intended to better understand the relationships between Doppler power and hematological and hemodynamic functions in the hope to expand medical applications of ultrasonic Doppler power imaging. It consists of both experimental and theoretical (numerical) studies. The experimental study was focused on the characterization of the effect of flow conditions on backscattered ultrasonic Doppler signals, i.e., the influence of flow turbulence and flow shear on Doppler power. Since the aggregation of red blood cells is a dominant factor to the ultrasonic backscatter, experiments regarding the effect of red cell aggregation on Doppler power from different aspects were also performed. All these experiments were performed in different flow loops designed for creating well-controlled flow conditions using specialized flow measuring instruments, e.g., a hot film anemometer for measuring the flow properties such as flow speed and turbulence intensity in situ. A commercial array scanner was used to semi-quantitatively demonstrate the basic phenomenon first and, for further studies, a single element ultrasonic flowmeter was also used to quantify the Doppler signal backscattered from blood. The results were compared to recently developed theoretical model of ultrasonic backscattering from an ensemble of cells.;In numerical analysis, scattering properties of single red blood cell and blood cell aggregate were modeled by solving the discretized integral Helmholtz equations. The morphology dependence was examined at different frequencies including those higher than 30 MHZ at which experiments are extremely difficult to perform at the present time. This method can be applied to investigate the effects of different forms of incident waves and different shapes of scatterers.