The Research Of Regularities Of Distribution Of The HIFU Field In Tissues Based On Finite Element Method

High Intensity Focused Ultrasound treatment is newly no-invasive and no-traumatic treatment method. The advantages of this method are as follow: firstly, it possesses the characteristics of high intensity, high reliability and fewer side effects. Secondly, it has high precision.. Thirdly, it can enter the body deeply without injury to normal organization. Thus, this method has caused people to pay more attention on it. When using HIFU to treatment,doctors must set the focal region on the ill region firstly. Hence, doctors should know the distribution of the sound field. The parameters in the tissues and water are different, so the distribution of sound field is different too. It has showed that the sound field will change by many experiments, when changing the acoustic parameters, including the distance between the tissue and transducers, the frame and the density of tissue and the velocity in the tissue.Because of these, it is necessary to control the distribution of the sound field of tissues for safe treatment. It can guide the clinical practice and improve the design of HIFU transducers.But all methods can not detect the sound field directly, and there are many difficulties in theory and exercising.. So it is a relatively direct method to know the sound field by modeling.There are many methods to simulate the distribution of sound field in tissues. The Numerical Method has exceeded the commonly Aanalytic Method along with the development of computer. Especially, the Finite Element Method(FEM) become more popular because of the advantage of analysing the complicated matter and boundary condition.So, compute the sound field in the tissue by FEM and find the rule of distribution when changing the parameters of the tissue, which are the emphasis of the paper. The innovations of the paper include:(1)Build the acoustic model by analyzing the process of HIFU treatment, and use the boundary condition to replace the vibration of the transducer. And, order the vibration to trend orientation to simplify the structure of the transducer. (2) Use the damping absorption to substitute the sound reflection on the interface between the fluid and the tissue.(3) Use the acoustic images from optical measurement to evaluate the reliability of the Finite Element to compute the sound field.(4) Model the distribution of Ultrasound field in the tissue, and at the point of the parameters of tissues, research the variational regularities, especially about the focus and foci.(5) Model the sound field in the tissue which are two layers, and found the variational regularities.The paper includes six parts. First, present the development of HFIU, the significance of the study and the researchful condition. Second, introduce some typical focused transducers, and build the physical model. Third, introduce the theory of Finite Element. Analyze the remedial process by HIFU, then build the acoustic and Finite Element model. Fourth, present the methods of computing sound field simply. Model the distribution of sound field in water by Rayleigh's integral, and measure the distribution of sound field by experiment. Fifth, model the sound field by FEM and found the rule in tissues. Sixth, summarize and expect the work.