Numerical Simulation Of Temperature Field In High Intensity Focused Ultrasound Therapy

Numerical Simulation of Temperature Field inHigh-intensity Focused Ultrasound TherapyHigh Intensity Focused Ultrasound is a new therapeutic technique for treatingparenchymatous tumor non-invasively. It has been used in treatment forparenchymatous tumor such as prostate cancer, liver cancer, malignant osteosarcoma,breast cancer and so on. Because of its micro-impassivity, less metastasis of cancercells, less sufferings of patients and fast recovery. But in clinical therapy,complications such as skin burn, nerve injury, residual of target tumor and so on mayoccur. In order to avoid these clinical complications, it is very necessary to monitorthe focal region temperature in real-time accurately and objectively and predict theshape and size of the focal region.Now, thermocouple probe has been usually used to measure temperature inclinic, but it's difficult for practical biosystem. CT, MR temperature measurementshaven't widely been used in clinic because of high price. Numerical simulationmethod can be used to predict practical focal region within human tissue bynumerical calculation. In recent years, HIFU nonlinear simulation has attracted moreattention of researchers. For example, KZK (Khokhlov-Zabolotskaya-Kuznetsov)proposed nonlinear acoustic theory during 1969-1971, many researchers adopteddifference time domain, frequency domain FDTD method, and analytical methods tosimulate nonlinear propagation of high-intensity ultrasound. But it's still far awayfrom direct application on simulation of nonlinear acoustic propagation in human softtissue with different acoustic properties and irregular characters. Nagayoshi Moritaproposed finite-difference time-domain (FDTD) nonlinear propagation of ultrasoundsimulation method, and studied the high intensity ultrasonic nonlinear propagation inwater referring to Reichenberger experiment in water and got exactly the samesimulation result with experimental wave shape.FDTD method which was proposed by Nagayoshi Morita to simulate pressure,velocity of nonlinear propagation high intensity ultrasound, together with Pennes bio-heat transfer equation is applied in this work to simulate temperature field inHIFU. 3-D cylinder coordinate is established referring to Hitachi prostate ultrasonictherapeutic system and FDTD method is used to resolve temperature fieldnumerically. Influence of space step distance, time step distance on precision ofpressure, energy and temperature. Then pressure, energy, temperature distribution,shape and size of 65℃above focal region as well as practical focus are simulated.Simulation results display that the focal region is in elliptical shape with length farlonger than diameter; the focal length produced by HIFU propagation in water is lessthan HIFU geometric focal length.This work simulates pressure, energy, temperature distribution, shape and size offocal region as well as practical focus and provides theory and method for clinicaltherapy. The results of this work are simulated in water; it's far away from humantissue. Simulation of human tissue is in the process of research.