高强度聚焦超声经颅治疗温度场的数值仿真研究

Research on Numerical Simulation of Temperature Distribution during Transcranial Tumor Therapy with High Intensity Focused Ultrasound

数值仿真是预测高强度聚焦超声(HIFU)温度场分布的有效方法之一。本研究参照人体头颅结构建立HIFU经颅骨治疗模型,采用Westervelt声波传播方程的近似式和Pennes生物热传导方程数值仿真HIFU经颅骨治疗的温度场分布,利用时间反转法对焦域位置进行调控和颅骨温度较高处的热点消除,进而分析讨论输入声强、辐照时间、换能器与颅骨相对距离对颅内形成焦域的影响。研究结果表明,时间反转法可实现HIFU经颅治疗形成焦域位置的调控和颅骨温度较高处的热点消除,热点消除后焦点温升无明显降低;利用热点消除法可在距离颅骨20mm的颅内浅表组织中形成60℃以上的焦域,形成的焦域体积随输入声强以及辐照时间的增加而非线性增加,声强越大,达到相同大小的焦域体积所需要的辐照时间越短,且换能器与颅骨之间的距离对颅内形成焦域体积的大小有影响。

Numerical simulation is one of the most significant methods to predict the temperature distribution in high- intensity focused ultrasound （HIFU） therapy. In this study, the adopted numerical simulation was used based on a transcranial ultrasound therapy model taking a human skull as a reference. The approximation of the Westervelt for- mula and the Pennes bio-heat conduction equation were applied to the simulation of the transcranial temperature dis- tribution. According to the temperature distribution and the Time Reversal theory, the position of the treatable focal region was corrected and the hot spot existing in the skull was eliminated. Furthermore, the influence of the expo- sure time, input power and the distance between transducer and skull on the temperature distribution was analyzed. The results showed that the position of the focal region could be corrected and the hot spot was eliminated using the Time Reversal theory without affecting the focus. The focal region above 60 ~C could be formed at the superficial tis- sue located from the skull of 20 mm using the hot spot elimination method and the volume of the focal region increa- ses with the exposure time and the input power in a nonlinear form. When the same volume of the focal region was obtained, the more power was inputted, the less the exposure time was needed. Moreover, the volume of the focal region was influenced by the distance between the transducer and the skull.