Experimental and theoretical quantification of focused ultrasonic cavitation intensity

Accurate characterization of ultrasonic cavitation is essential for safe and efficient ultrasound therapy. In this study, a synchronous acquisition system using a hydrophone and a high-speed camera was employed to observe the cavitation field generated by 994 kHz focused ultrasound within a power range of 20 W-400 W. Two quantitative indicators, the Broadband Integrated Pressure (BIP) and the image-gray-scale-based Cavitation State Variable (Q), were utilized to characterize the cavitation intensity. Theoretically, a computational method for cavitation intensity combining bubble cluster dynamics with an acoustic radiation model was proposed, establishing a quantitative analytical relationship between microscopic bubble dynamics and macroscopic cavitation intensity. The results indicate that the evolutionary trends of the experimentally measured BIP and Q with increasing driving power are highly consistent with the theoretical calculations, which demonstrated the effectiveness and complementary nature of the dual acoustic-optical evaluation system in quantifying cavitation intensity. This study clarifies the power-dependent mechanism of focused ultrasonic cavitation intensity, providing both a theoretical foundation and experimental support for precise cavitation control and dose optimization in clinical applications.