Dept. of Instrum. Eng., Shanghai JiaoTong Univ., Shanghai 200030, People's Republic of China
In the ultrasonic hyperthermia for cancer therapy, for keeping the heating temperature in a certain range and avoiding problems from needle insertion, noninvasive monitoring of temperature is needed and has been developed. Using the bioheat transfer equation including thermal source, the temperature distribution at times has been calculated by the finite element method under certain boundary conditions. The influence of the focusing, tumor size, blood perfusion, and temperature of skin, etc., on the temperature field inside the human body, has been investigated. It is found that good control of the power emission can be made by measuring the skin surface temperature which has a definite relation with that at the focus under a certain group of parameters. It has also been found that the temperature at the equilibrium state due to the balance between sound power deposition and heat diffusion by blood perfusion can be calculated. This law can also be used to control the ultrasonic power emission for hyperthermia. The change of the temperature distribution corresponding to a change in the depth of focus has been investigated in detail. This can help to make the effective heating area enough to cover the whole cancer, so as to improve the efficacy of the therapy.