时间反转聚焦在组织中形成损伤的数值建模

为考察基于时间反转方法的高强度聚焦超声治疗在预设目标点处的组织损伤情况,使用三维有限差分算法求解Westervelt方程,建立非线性声波传播数值模型,采用97阵元相控阵结合虚拟源的时间反转方法进行超声聚焦,分析其形成的声场和热场,并考察目标点偏离轴线时的组织损伤形成规律。结果表明随着目标点偏轴距离的增大,声压旁瓣开始增多。旁瓣的温升较低,不足以形成组织损伤。时间反转方法可用于多点聚焦,在一定的范围内,形成多点目标损伤而不产生额外的周围组织损伤。同时多点聚焦可以形成一个较大的损伤区域,减少超声治疗时间。

Numerical study of tissue lesion created by time reversal focusing method*

Tissue lesion formation in high intensity focused ultrasound at preset target location using time reversal method are studied. Based on nonlinear Westervelt equation and bio-heat equation, a 3-D FDTD algorithm is realized to build a numerical model and to analyze the sound field and temperature field. In this model, virtual source time reversal method for 97 element phase array transducer is used to focus at off-axis position, and its lesion distribution is investigated. The results show that side lobes grow as the increasing of off-axis distance. The temperature at side lobes is not high enough to create lesion. Time reversal method can be used in multi targets pattern. By this method, lesions can be formed in certain off-axis distance without unwanted lesions, and a large volume of lesion can be created simultaneously to reduce the treatment time.