Bifrequency excitation for extracorporeal ultrasound thrombolysis

Abstract

A bifrequency excitation consisting of two neighboring frequency components can reduce intensities needed to achieve strong inertial cavitation activities. We present in-vitro experimental results aiming at testing such a bifrequency excitation for extracorporeal ultrasound thrombolysis. In a first set of experiments, human blood clots were inserted in small tubes filled with saline and placed at the focus of a piezoelectric transducer. The efficiencies of mono- (550 kHZ) and bifrequency (535 and 565 kHz) excitations were compared for (spta) intensities ranging from 50 to 160 W/cm2, and a passive recording of the cavitation activity was performed during treatment. A modified setup enabled to measure the size distribution of the debris resulting from thrombolysis experiments realized under flow. A comparison of the spatial temperature distribution for each type of excitation was performed in another set of experiments using MR temperature imaging. Under the conditions of the experiments, 80% of thrombolysis was achieved with a monofrequency intensity of 150 W/cm2, while 80 W/cm2 were sufficient with a bifrequency excitation. Mean debris size was reduced by the use of a bifrequency excitation, and MR temperature imaging showed that, for a given intensity, the spatial temperature distributions are the same for both types of excitation.