聚焦超声作用下空化活动演变及其监测方法

The evolution and monitoring method of cavitation activity under focused ultrasound

高强度聚焦超声是实现肿瘤热消融的有效治疗方式。对超声治疗过程中的空化活动进行实时监测,对于保障治疗的安全性和有效性具有重要意义。该研究搭建了聚焦超声作用下仿生物组织体模和离体牛肝组织的被动空化检测和驱动功率监测系统,并使用显微镜记录了体模在超声作用过程中气泡和损伤的发展过程,分析了气泡发展过程与空化信号变化的相关性。实验表明:体模在电功率150 W的超声辐照过程中,沸腾气泡产生前未见宽带噪声幅值增加;6 s时体模内产生沸腾气泡,气泡破裂后产生大量空化核并形成空化泡群,宽带噪声幅值开始增长,此后泡群逐渐向换能器方向发展;在泡群停止向换能器端发展后,靠近换能器端的微小气泡逐渐融合产生沸腾气泡,惯性空化强度在沸腾气泡屏蔽下逐渐下降;沸腾泡产生和破灭时,驱动功率和回波信号中的谐波幅值同步出现大幅波动;在离体牛肝组织中,随声强的增加沸腾空化发生时刻逐渐提前。实验结果证明了沸腾气泡的产生及破裂,会促进惯性空化的发生。因此在不同强度的聚焦超声辐照下,可以通过调节辐照时间避免剧烈空化活动发生。

High intensity focused ultrasound is widely used in clinical non-invasive treatment of tumors.Real-time monitoring of cavitation activities during ultrasound treatment is of great significance to ensure the safety and effectiveness of treatment.In this study,a passive cavitation detection and driving power monitoring system for bionic tissue phantom and isolated bovine liver tissue under focused ultrasound was established.The development process of bubbles and damage in the phantom during ultrasound was monitored by microscope,and the correlation between bubble developing processes and cavitation characteristic signal changes was analyzed.The experiment shows that there is no increase in the amplitude of broadband noise before the boiling bubbles are generated during the ultrasonic irradiation of the phantom under 150 W electric power.Boiling bubbles are generated in the phantom at 6 s,after its rupture,a large number of cavitation nuclei are generated and cavitation bubble groups are formed,the broadband noise amplitude begins to increase,and then the bubble group gradually develops towards the transducer.When the bubble group stops developing to the transducer,the tiny bubbles near the transducer gradually merge to generate boiling bubbles,and the inertial cavitation intensity gradually decreases under the shielding of boiling bubbles.The generation and breaking of boiling bubbles will lead to large fluctuations in driving power and amplitudes of harmonics in the backscattering signal synchronously.In isolated bovine liver tissue,the occurrence time of boiling cavitation gradually advanced with the increase of sound intensity.The experimental results show that the generation and rupture of boiling bubbles will promote the occurrence of inertial cavitation.Therefore,under the irradiation of focused ultrasound with different intensities,severe cavitation activity can be avoided by adjusting the irradiation time.