Ultrasonic Coagulation of Large Tissue Region by Generating Multiple Cavitation Clouds in Direction Perpendicular to Ultrasound Propagation

High-intensity focused ultrasound (HIFU) therapy is attracting attention as a minimally invasive therapeutic modality. However, it has a problem of a long treatment time. To improve the efficiency of the treatment, we developed a method of coagulating a large region at one time utilizing multiple clouds of cavitation. It is known that acoustic cavitation generated in the focal region of HIFU enhances tissue heating. In this study, cavitation clouds were generated at three positions in the direction perpendicular to ultrasound propagation using high-intensity ultrasound pulses. The tissue in the vicinity of the cavitation clouds was coagulated simultaneously with nonspherically focused ultrasound waves at a relatively low intensity. A high-speed camera was used to observe such behavior of cavitation clouds in a tissue-mimicking gel and to optimize the sequence, and the coagulation performance of the sequence was confirmed with an experiment using excised tissue. The result suggests that the HIFU treatment time is significantly shortened by employing the proposed method.