In the sonodynamic treatment, reactive oxygen species (ROS) are generated to damage cancer cells. The efficient generation of ROS, therefore, is significant for the treatment. The trigger high-intensity focused ultrasound (HIFU) sequence, consisting of an extremely high intensity short trigger pulse followed by a medium-intensity and long sustaining burst, was tested for this purpose, with and without scanning the focus, in this study. The distribution of generated cavitation bubbles was observed using a high-speed camera and the amount of generated ROS was quantitatively determined by the KI method. As a result, the trigger HIFU sequence generated several times more ROS than the trigger pulse alone, and the sequence with scanning the focus generated more than twice the amount of ROS than that without scanning the focus when the intermission time between the trigger pulse and the sustaining burst was considered. These suggest that the trigger HIFU sequence with scanning the focus is efficient for generating ROS.

Sonodynamic treatment is a non-invasive cancer treatment using ultrasound through the generation of reactive oxygen species (ROS) by acoustic cavitation. High-intensity focused ultrasound (HIFU) can generate cavitation bubbles using highly negative pressure in its focal region. When cavitation bubbles are forced to collapse, they generate ROS, which can attack cancer cells, typically assisted by a sonodynamically active antitumor agent. For sonodynamic treatment, both localization and efficiency of generating ROS are important. To improve them, the region of ROS generation was quantitatively estimated in this study using a polyacrylamide gel containing luminol as the target exposed to “Trigger HIFU”, consisting of a highly intense short “trigger pulse” to generate a cavitation cloud followed by a moderate-intensity long “sustaining burst” to keep the cavitation bubbles oscillating. It was found to be important for efficient ROS generation that the focal region of the trigger pulse should be immediately exposed to the sustaining burst.

Sonodynamic treatment (SDT) is a non-invasive cancer treatment using ultrasound, reactive oxygen species (ROS) generated by acoustic cavitation bubbles, and sonodynamically active antitumor agents. When cavitation bubbles collapse, they generate ROS, which can attack cancer cells by their cytotoxicity. For SDT, both localization and efficiency of generating ROS are important. In this study, high-intensity focused ultrasound (HIFU) was employed for localization and "Trigger HIFU" sequence was further employed for generating cavitation and ROS efficiently even under the progressive wave condition. A polyacrylamide gel containing luminol was employed to visualize the region of ROS generation by utilizing sonochemiluminescence of luminol. Focus scanning methods were thereby tested to further improve the ROS generation efficiency. In focus scanning irradiation, the time interval considering the bubble lifetime and the inter-focal distance considering the sidelobes were found to be important for efficient generation of ROS.

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