There are reports that ultrasonically induced cavitation bubbles locally enhance tissue heating in high intensity focused ultrasound (HIFU) treatment. In this study, a high-intensity burst (named ''a triggering pulse'') above the cavitation threshold was used to trigger cavitation. Immediately after that, CW ultrasound (named ''heating waves''), at an intensity level and duration typical for conventional HIFU ablation was irradiated. Before the ablating sonication, it is necessary to determine the optimum intensity and duration of the triggering pulse. Immediately after a test triggering pulse, low-intensity CW ultrasound (named ''a sustaining pulse'') was irradiated for a short duration of time, and we detected the cavitation noises (subharmonics and higher harmonics) generated in the focus spot. The relationship between the 1/2 subharmonic signal amplitude and the coagulation volume after the ablating sonication was investigated. The result of this experiment suggests that we can optimize the triggering pulse by detecting the 1/2 subharmonic signal amplitude. #

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.

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High-intensity focused ultrasound (HIFU) is a type of therapeutic treatment in which ultrasound is focused to a target tissue such as cancer to be thermally coagulated. To enhance the safety and accuracy of HIFU treatment, a noninvasive method of monitoring the thermal lesion formation is important. A potential method for this purpose is ultrasound imaging. In this study, high-speed imaging by parallel beamforming was performed using ultrasound RF signals acquired during HIFU exposure, and the distribution of the cross-correlation coefficient between RF frames was calculated to estimate the tissue coagulation. Using high-speed imaging, HIFU can be irradiated quasi-continuously. The result shows that the decorrelation was observed at and around the focal spot of HIFU exposure. The decorrelation was induced by the change in RF signals owing to tissue coagulation, which was confirmed by the fact that the emergence and increase in the number of decorrelated pixels at and around the focal spot corresponded to the start and progress of tissue coagulation.

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