Theoretical Study On The Reason That Affects The Distribution Of Tissue Heat Source And Temperature In The Process Of Thermotherapy By Ultrasound

According to the prediction of WHO, malignant tumor will be the first killer to human health in the 21th Century. As far as the actual condition is concerned, any single conventional cancer treatment available (resection, chemotherapy or radiotherapy)can hardly be a radical therapy to the patient with malignant tumor, especially those with middle or late stage ones on admission. Heat treatment for cancer can induce the death of cancer cells. High Intensity Focused Ultrasound, a more advanced technique developed rapidly in the later years, can bring beams of ultrasound to a tight focus within deep-seated tumor tissue and produce rapid and intense heating effect causing prompt tissues ablation, whereas the intervening tissues within the beam path and the surrounding normal tissues remain intact. As an effective and noninvasive local palliative therapy for tumors, High Intensity Focused Ultrasound begins to receive much attention in the cancer thermotherapy.However, as the research of the technique of High Intensity Focused Ultrasound more and more advanced, people found that the theory of how to improve the success and efficiency of ultrasonic thermotherapy is unripe. The problem include following aspects. For example, how to confirm the point and shape of treatment with ultrasound, how to make sure the ultrasonic indorse in the process of treatment, how to choose the best way of scanning and the distribution of ultrasonic focus, how to calculate the temperature distribution of treatment area, how to optimize the heat way and compare theoretical result with experimental result. Therefore, it is also need more investigations to perfect the theory of ultrasonic thermotherapy.In this paper, numerical simulation was used, the reason that affects the distribution of heat source and temperature in the process of heat treatment by ultrasound was partly found. The following work has been done:(1) The theory of ultrasonic thermotherapy has been illustrated. Based on High Intensity Focused Ultrasound, the mechanism that matter is affected in focus sound field has been discussed, and several focus sound field are also concluded;(2) Contrasted several bioheat conduction models, the Pennes model is the better one. Based on the Pennes model and Matlab tool, the same soft tissue in the process of treatment with focus ultrasound, its heat source distribution is decided by following factors: frequency, radius and aperture of sound source. It is that the heat source shape reduce is related with increasing frequency and aperture, decreasing radius of sound source.(3) The influence that parameter of sound and tissue for temperature distribution is analyzed. Based on Matlab tool, the Pennes bioheat conduction equation is solved. Following is conclusion:a. The influence that parameter of sound sourceThe more increase aperture, frequency and decrease radius of sound, the more reduce temperature rise in tissue; because of sound attenuation, the temperature rise at sound focus reduce following high frequency;b. The influence that parameter of tissueThe more increase of the attenuation coefficient and ruduction of the heat conduction coefficient, the more rise of the temperature in tissue quickly, because of high attenuation coefficient, the influence that attenuation coefficient change affects temperature rise at sound focus is small; when the heat conduction coefficient increase, temperature rise slowly, but can get to state temperature rapidly...