Development of efficient method of generating reactive oxygen species by expanding cavitation region using ultrasound focus scanning in the direction of ultrasound propagation

Sonodynamic therapy is a minimally invasive high-intensity focused ultrasound (HIFU) based therapy that combines a sonosensitizer and reactive oxygen species (ROS), which are produced by acoustic cavitation. In this paper, we experimentally examined the effectiveness of a proposed method of scanning the ultrasound focus in the direction of HIFU propagation for continuously generating cavitation clouds to expand the region of ROS generation and increase the amount of ROS. First, the continuous generation of cavitation bubbles was observed using a high-speed camera, and it was confirmed that bubbles could be generated even with a short-duration HIFU, which is difficult to generate bubbles by itself. Subsequently, we evaluated the area and amount of ROS generation by imaging sonochemiluminescence. Comparing the irradiation at 1 point with that at 7 points, the amount of ROS per acoustic energy increased by about 1.5 times, suggesting that it is an efficient method for ROS generation.