The Research On Control Method Of Sound Field And Temperature Field For High Intensity Focused Ultrasound Therapy

High Intensity Focused Ultrasound (HIFU) therapy has been successfully used in treating a variety of tumors. The treating principle is that:the ultrasound transducer is used to focus acoustic energy into tumor area, which leads to tissue protein coagulation necrosis through a variety of effects, especially the thermal effect. At the same time, the surrounding normal tissue is safe. In clinical application, sometimes skin burns, calcification, inadequate treatment, nerve injury occurs because of time-delay, over-shoot, oscillation, longer treatment-time and other reasons during HIFU therapy. Therefore, the control of sound intensity and temperature in target area during treatment is extremely important.In this thesis, the simulation of sound field and temperature field induced by different transducer in biological tissue is based on the bio-heat conduction models. Influence of various parameters on sound field is analyzed, and a kind of thermal control method is proposed. All work done as follows:1. A biological tissue model is established. Bio-heat conduction problem, calculation method of focused acoustic field and related fuzzy control theory are investigated.2. Research on sound field in single biological media and multiple biological media induced by concave spherical transducer is done. Influence of sound sources and tissue parameters on sound field is analyzed. The results show that:larger sound speed or lower frequency leads to larger maximum sound pressure and shorter focal length. Larger initial sound pressure or smaller absorption coefficient leads to larger maximum sound pressure, but the focal length is almost unchanged. Thickness changed in certain layer of multiple biological media influences the maximum sound pressure in focal zone.3. Pseudo-inverse algorithm is used to calculate sound fields in biological media induced by plane phased array transducers. Influence of different parameters on sound field is analyzed. The results show that: larger array element space or smaller array element width lead to smaller maximum sound pressure. Different transducers can’t be drove by the same drive signal. Different media parameter may lead to different focal zone. Changes of absorption coefficient or thickness in certain layer on multiple biological media influence the sound pressure on focal zone. Multiple-focus is formed by changing transducer’s drive-signal, and it can be used in the treatment of large tumor.4. A fuzzy control method is used to control temperature in HTFU therapy. Temperature control in single-layer media and multi-layer media with concave spherical transducer is studied, and temperature control in single-focus and multiple-focus with plane phased array transducer is studied too. This method is compared with traditional PID controller. The result is that:fuzzy control is better than traditional PID control. It can avoid time-delay, overshoot, oscillation, longer treatment-time, which appeared in traditional method.A lot of simulation experiments are done in this thesis. Influence on sound fields is obtained by analyzing different parameters, and a way to optimize the sound field is found. A fuzzy control method is proposed in HIFU therapy, which can improve safety and efficiency. The work done here has significance to HIFU therapy application. The results have some reference value in selecting the therapeutic dose.