High-intensity focused ultrasound heating of large tissue region enhanced by cavitation bubbles at multiple focal spots

High-intensity focused ultrasound (HIFU) causes selective tissue necrosis through heating and is used for a noninvasive treatment of cancer therapy. However, it has a problem of a long treatment time for a large tumor. To improve the throughput of the treatment, the development of a highly efficient method is needed. It is known that cavitation bubbles enhance the heating effect of ultrasound during ultrasonic irradiation because the increase in the energy dissipation is caused by the volumetric oscillation of cavitation bubbles. In this study, cavitation bubbles were generated at multiple spots by changing focal position of high-intensity ultrasound. Immediately after generating the bubbles, the bubbles were exposed to a wide-focused ultrasound which covers all the cavitation sites for the cavitation-enhanced heating in a large region. The behavior of the cavitation bubbles at multiple spots in a tissue-mimicking gel was observed by high-speed photography, and the coagulation performance of the developed sequence was confirmed with an experiment using excised tissue. The results showed high efficacy of the proposed method for to coagulate a large tissue region.