时间反转方法用于高强度聚焦超声的焦点偏移补偿

Focus-shift compensation in high intensity focused ultrasound using the time reversal method

传统的高强度聚焦超声(HIFU)治疗中实际焦点和预设焦点容易出现偏移,为考察时间反转方法对HIFU治疗中焦点偏移的补偿效果,采用时域有限差分方法求解Westervelt方程,建立高强度聚焦声场数值模型。数值计算得到在人体软组织中进行HIFU治疗时,采用时间反转方法后焦点偏移距离最大仅为1.6 mm。脂肪层厚度及声源强度改变对时间反转聚焦精度影响不大,F数(焦点距离同换能器孔径的比值)降低时,焦点偏移减小。研究表明在人体软组织吸收系数和非线性系数范围内,时间反转方法可有效补偿焦点偏移,达到更好的聚焦效果。

The actual focal point can deviate from the desired point in the traditional treatment of high intensity focused ultrasound （HIFU）. In order to investigate the focus-shift compensation effect of HIFU by the time reversal method, we solved the Westervelt equation using the finite difference time domain method, and established a numerical model of HIFU field in layered tissues. Numerical simulation shows that the maximum deviation of the focus point is decreased to 1.6 mm after using the time reversal method. The thickness of fat layer and the source intensity have negligible effects on the time reversal focusing accuracy, while the deviation of the focus decreases when lowering the F number （the ratio of focal length and aperture）. The study indicates that when the nonlinearity and absorption parameters change in the range of that of human tissue, the time reversal method can compensate the focus-shift effectively and has a better focusing quality.