Method of spatiotemporally monitoring acoustic cavitation based on radio frequency signal entropy analysis

Abstract

The violent inertial cavitation effect generated during high intensity focused ultrasound (HIFU) treatment may damage healthy tissues around the target area. Therefore, it is urgent to develop new technical approaches that can quantitatively monitor the acoustic cavitation motions in biological tissues with high precision in space and time, so as to ensure clinical safety and effectiveness. Compared with the traditional commercial ultrasonic gray value signal, the ultrasonic radio frequency (RF) signal can well retain more detailed information about the acoustic scattering signal. As a statistical parameter not based on mathematical function model, the information entropy can characterize the spatiotemporal evolution state of disorder of scatters inside tissues resulting from acoustic cavitation. Therefore, this paper proposes a real-time monitoring system for spatiotemporal evolution of acoustic cavitation based on the entropy analysis of ultrasonic RF signals. First, the original RF signal of scattered echoes generated by HIFU-induced cavitation bubbles inside the gel phantom is obtained by using a modified B-ultrasound system, and the two-dimensional mean filtering method is used to suppress the HIFU-induced strong interferences overlapping with cavitation monitoring imaging signals. Then, the dynamic variation range of the RF signal is expanded through data standardization processing, and the entropy image is reconstructed based on the sliding window information entropy analysis to demonstrate the spatiotemporal evolution status of the HIFU-induced cavitation behanviors. The experimental results indicate that the acoustic cavitation imaging algorithm based on RF signal entropy analysis should be more sensitive and accurate than the B-model gray scale imaging method for determining the onset time and spatial position of cavitation activities, which is helpful in ensuring the safety and efficacy of HIFU clinical treatment. Thepresent work will provide a useful tool for the spatiotemporal monitoring of the acoustic cavitation generated in tissues during HIFU treatment, and lays a solid theoretical and experimental foundation to establish an effective quantity-effect evaluation system for the cavitation related biological effect.