A novel approach to identify the thermal mechanism in high- and low- frequency focused ultrasound thermal ablation process

The purpose of this study is to propose a novel approach to identify the thermal mechanism during the high- and low- frequency focused ultrasound thermal ablation process, and to verify that the occurrence of the ultrasound-induced macroscopically visible bubbles exert another key effect in thermal lesion formation during the focused ultrasound thermal ablation process. In our experiments, consecutive sonications with orthogonal intersections were applied to observe the thermal lesion interaction induced by 577- or 1155-kHz ultrasound. Results showed that the 1155-kHz heating was dominated by ultrasound energy absorption, with blocking of consecutive sonications being evident only rarely. However, in 577-kHz sonications, the thermal process was dominated by inertial cavitation and the corresponding ultrasound-induced macroscopic visible bubbles, which was verified form the later lesion been blocked by the former one and direct observation from light microscopy. This study demonstrates that the operating frequency for ultrasound thermal ablation should be selected based on the intended specific thermal mechanisms to be induced.