A technique for monitoring and controlling cavitation activity during high intensity focused ultrasound application

Abstract

It has been reported that cavitation can lead to enhanced heating in the focal region of a HIFU source. In order to exploit this heating for in vivo use, it is essential that the cavitation only occur in the focal region. Thus, the onset and evolution of inertial cavitation activity must be monitored and controlled during HIFU therapy. One candidate sensor is a confocally-aligned passive cavitation detector; however this would add complexity to a clinical HIFU applicator. Instead we propose that the HIFU source itself can serve as a monitoring device. The combination of broadband acoustic emissions (inertial cavitation) and backscatter (stable cavities) emanating from the HIFU focus manifests itself as fluctuations of the otherwise constant driving voltage amplitude, providing a convenient means for sensing cavitation activity. We will present results of experiments assessing the feasibility of using the variance in the amplitude of the HIFU drive voltage as a feedback control signal. Success is determined by the shape of the lesion created using supplemental control compared to the shape obtained otherwise. Two independent control parameters were used: the amplitude and the duty cycle of the HIFU. [Work supported by the Department of the Army award DAMD17-02-2-0014.]