聚焦超声在脱气水声场中的多泡分布与声致发光研究

为明确多泡空化在高强度聚焦超声（High intensity focused ultrasound，HIFU）治疗中焦前区、焦后区的副作用，进一步优化HIFU治疗，本文在不同声强下利用高速摄像系统与数字相机拍摄聚焦超声在脱气水声场中的多泡及多泡声致发光（Multi-bubble sonoluminescence，MBSL）的空间分布，通过被动空化检测（Passive cavitation detection，PCD）技术和光电倍增管（Photomultiplier tube，PMT）系统检测多泡空化特征及声场整体发光强度。研究表明：当声强较低时（如3 047 W/cm²），气泡以驻波场模式分布；随着声强的提高，焦点处出现向焦后方生长的气泡群，3~6 MHz宽带噪声增幅明显，同时MBSL最先出现在焦前区，并向换能器表面扩大，声场整体发光强度与声强成正比；当声强足够高时（如21 328 W/cm²），焦点处空化泡群剧烈坍缩的同时可见椭球形光斑，嘶嘶声不断，气泡的聚集大大降低了声场的相对发光强度。

Study on Multi-bubble Distribution and Sonoluminescence in Focused Ultrasound Field Mediated with Degassed Water

To clarify the side effect of multi-bubble cavitation at pre-focus and post-focus in high intensity focused ultrasound (HIFU) treatment and further optimize HIFU treatment, this paper records the spatial distribution of multi-bubble and multi-bubble sonoluminescence (MBSL) at different acoustic intensities in the focused ultrasound field mediated with degassed water using high-speed camera system and digital camera, respectively. Besides, the cavitation characteristics of multiple bubbles and the overall luminous intensity of sound field are separately detected by passive cavitation detection (PCD) technology and photomultiplier tube (PMT) system. It is found that when acoustic intensity is low (such as 3 047 W/cm²), bubbles distribute as a typical standing wave pattern. With the increase of acoustic intensity, a cluster of bubbles gathers at focus, then grows towards post-focus, and 3-6 MHz broadband emissions increase monotonically. Moreover, MBSL firstly occurrs pre-focus and is enlarged towards the surface of the transducer, and the overall luminous intensity of the sound field is proportional to acoustic intensity. When acoustic intensity is sufficient (such as 21 328 W/cm²), the cavitation bubbles at focus collapse tempestuously with a continuous hiss, and an elliptical bright spot appears at focus. The accumulation of bubbles sharply weaken the overall luminous intensity of the sound field.