Highly efficient cavitation-enhanced heating with dual-frequency ultrasound exposure in high-intensity focused ultrasound treatment

High-intensity focused ultrasound (HIFU) treatment is a noninvasive therapy for malignant as well as benign tumors. In this method, the ultrasound is generated outside the body and focused to the target tissue. Therefore, physical and mental stresses on the patient are minimal. A drawback of HIFU therapy is the long treatment time for a large tumor owing to a small therapeutic volume by a single exposure. Enhancing the heating effect of ultrasound by cavitation bubbles may solve this problem. They are generated by high-intensity ultrasound exposure and can convert the acoustic energy into heat at a high efficiency. In this study, we combined "dual-frequency ultrasound exposure" for the efficient generation and expansion of a cavitation bubble cloud, and "multiple-triggered HIFU" for the efficient enhancement of ultrasonic heating. The result suggests that the newly proposed combined method is more efficient than the conventional triggered HIFU method.