Effect of inter-focal distance and interval time in focus scanning of high-intensity focused ultrasound on efficiency of reactive oxygen generation

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.