Numerical simulation of the tissue ablation in high-intensity focused ultrasound therapy with array transducer

The development of high-intensity focused ultrasound (HIFU) therapy for deeply situated cancer has been desired. One problem is focal point displacement due to the inhomogeneity of the human body. The objectives are the realization of appropriate phase control of an array transducer and support for preoperative planning of HIFU therapy by the computational prediction of ablation regions. To these ends, in this study we have developed an HIFU simulator that employs a voxel phantom constructed from CT/MRI data of a living human body. To reproduce the pressure propagation through an inhomogeneous medium, the mass and momentum equations for a mixture with the equation of state of the medium are solved. The ablation of tissue is modeled as a phase transition by using the phase field model. Then, the heat equation with viscous dissipation as a heat source and the Allen-Cahn equation with a free energy model are solved to predict the development of the ablation region. The basic equations are discretized by the finite difference method. HIFU therapy with an array transducer for liver cancer is reproduced numerically. Although the results without phase control show displacement and diffusion of the focal point due to the inhomogeneity of the human body, a clear focal point is obtained by using the array transducer with an appropriate phase delay obtained from pre-computation. The HIFU simulator predicts that the ablation region will develop close to the target, owing to the phase control of the array transducer.