Inertial cavitation enhancement using confocal ultrasound

Abstract

Inertial cavitation has been shown to be useful in many therapeutic applications; thus, controlling this phenomenon is of great therapeutic interest. However, the stochastic nature of cavitation often proves problematic for predicting its location and extent. Traditional solutions to this problem are the of use dedicated detection apparatuses, or to use injectable microbubbles (MBs), which act as nuclei for the initiation of cavitation. We hypothesize here that cavitation can be reliably controlled without the use of MBs using a confocal system, which produces a lobular focal zone due to acoustic interference. This interference pattern was studied both in simulation and hydrophone measurement. Cavitation extent was confirmed chemometrically with an assay for hydroxyl radical formation, and by passive cavitation detection with a hydrophone. A high speed camera was used to image the initiation of cavitation within the focal zone, the evolution of the bubble cloud, and the subsequent bubble rebound after pulse cessation. The experiments in this work confirm that cavitation is produced more reliably in the confocal setup as opposed to a single transducer, as well as illuminating the mechanisms for this enhancement. [Work supported by the European Union through the Eurostars program (project E!6173) and Caviskills SAS.]