Development of Numerical Simulator for Extracorpreal Shock Wave Lithotripsy System Using Numerical Phantom

采用有限元方法，建立了体外冲击波碎石数值模拟系统。该模拟器由两部分组成：一是电磁感应换能器模拟器，二是非线性声传播模拟器。电磁感应换能器模拟器可以分析包括声辐射在内的瞬态响应。在空间上用轴对称有限元法建立了磁-力-声耦合系统的计算公式，然后在时间域上进行了求解。给出了具有较好聚焦能力的圆板散热器和浅球壳散热器的数值算例。然后对制作的小尺度模型进行了实验验证。通过比较，验证了本文数值模拟的有效性和能力。非线性声传播数值模拟器可以分析声音在人体等非均匀声介质中的传播。采用二维有限元法在计算机上对人体进行数值模拟，该模型被称为“数值幻影”。然后，对一些数值幻象进行了数值例子的演示，其中包括岩石病。通过分析可以得出以下结论：1)当结石体位于冲击波碎石机的焦点位置时，由于结石体对冲击波具有良好的散射和衍射作用，可以获得较高的破坏能力，并使结石体周围的组织免受高强度冲击波的伤害。2)当结石位于离焦处时，破坏能力下降，穿透结石的冲击波对病灶处的正常组织造成损伤。

A numercal simulator for extracorpreal shock wave lithotripsy is developed using the finite element method. The simulator consists of two part : one is the simulator for the electromagnetic induction transducer and another is for the nonlinear sound propagation. The simulator for the electromagnetic induction transducer can analyze the transient response including sound radiation. The formulation is made for coupled magneto-mechano-acoustic system using the axisymmetric finite element method in space, then the solution is made in time domain. Some numerical examples are demonstrated for a circular plate rediator and a shallow spherical shell radiator which has a better focusing capability. Experimental verification is then made for the fabricated models of small scale. The comparison proves the validity and the capability of the present numerical modeling.The numerical simulator for the nonlinear sound propagation can analyze the sound propagation in inhomogeneous acoustic media such as human body. The human body is numerically modeled on computer using two dimensional finite element method and the model is called 'numerical phantom'. Numerical examples are then demonstrated for some numerical phantoms including the lithiasis. The following could be deduced from the analysis : 1) When the lithiasis is located at the focal point of the shock wave lithotriptor, the high destruct capability can be achieved and the tissue surround the lithiasis is kept the safety from the high intense shock wave because the shock wave is well scattered and diffracted by the lithiasis. 2) When the lithiasis is located at out of focus, the destruct capability is degraded and the normal tissue at the focal position is injured by the shock wave which penetrates the lithiasis.