超声热疗时生物组织内热源与温度分布的理论研究

发布时间：2018-06-29 03:27

本文选题：超声热疗 + 生物热传导方程　；参考：《陕西师范大学》2007年硕士论文

【摘要】： 根据WHO预测：恶性肿瘤将成为21世纪危害人类健康的头号杀手。但就目前情况而言，对于一些肿瘤特别是中晚期肿瘤，任何一种常规治疗(手术切除、化学疗法或放射疗法)均不能单独成为一种根治肿瘤的手段。肿瘤温热治疗是通过超声加热肿瘤组织而促进肿瘤细胞的死亡。高强度聚焦超声技术则是近几年快速发展的先进热疗技术，它能将超声波聚焦于深部肿瘤组织，通过高热效应使肿瘤组织在短时间内凝固坏死，而对超声波所穿过的组织和靶区周围的正常组织没有损伤。高强度聚焦超声技术作为一种有效的和非侵入性的肿瘤治疗方法已开始引起肿瘤热疗领域的关注。然而，，随着对高强度聚焦超声技术研究的不断深入，发现在超声热疗的过程中，关于如何提高超声热疗的治愈成功率和治疗效率的相关理论还不成熟。这方面的问题涉及：治疗靶区解剖位置和几何形状的确定、治疗热剂量的确定、最佳声焦点分布或最佳扫描路线和扫描速度选取、治疗区域温度分布计算、热区计算结果与预定加热指标的比较和加热方法的优化。因此，要完善超声加热治疗的理论，还需做大量的研究、探索工作。本文通过数值模拟的方法，探讨了超声热疗时，影响生物软组织内热源与温度分布的因素。主要工作和相关结论如下所示： (1)阐述了超声热疗技术的基本原理，以高强度聚焦超声技术为例，详细介绍了聚焦超声对处于其声场中的物质的作用机理，并归纳总结了几种常见的医用聚焦声场； (2)对比了几种生物热传导模型，得出Pennes生物热传导模型是目前比较理想的模型。并以该模型为基础，运用Matlab数学工具，讨论了对于同一生物软组织，在被聚焦超声加热时，其内部的热源分布由下列参数决定：声源频率f、换能器曲率半径R及孔径半径a。数值模拟结果显示：聚焦声场中的生物组织内热源的分布区域随着超声频率的增高、换能器孔径半径的增加、换能器曲率半径的减小而不断变小。 (3)分析了声源参数和生物组织参数对组织温度分布的影响。运用Matlab的pdetool工具，求解了Pennes生物热传导方程，得到的结论是： a．声源参数对生物组织温升的影响换能器曲率半径越小、孔径半径越大、超声频率越高时，组织内温度上升越快、越多。几何焦距及换能器半径对升温快慢及大小的影响很突出；超声频率越高时，因为衰减作用，声焦点处的升温快慢及大小随频率变化较小。 b．生物组织特性参数对组织温升的影响衰减系数越大、热传导系数越小时，组织内温度上升越快。当衰减系数较大时，衰减系数的变化对声焦点处温升快慢和大小的影响相对较小；热传导系数较大时，温度上升较小，但达到稳态温度所需的加热时间也越短。
[Abstract]:According to WHO forecast: malignant tumor will become the first killer of human health in the 21 st century. However, as far as the present situation is concerned, no conventional therapy (surgical resection, chemotherapy or radiotherapy) can be used to cure the tumor alone for some tumors, especially in the middle and late stage. Tumor hyperthermia therapy promotes tumor cell death by ultrasound heating of tumor tissue. High intensity focused ultrasound (HIFU) is an advanced hyperthermia technique developed rapidly in recent years. It can focus ultrasound on deep tumor tissue and make tumor tissue coagulate and necrosis in a short time by high heat effect. There was no damage to the tissue through which the ultrasound went and the normal tissue around the target area. As an effective and non-invasive tumor therapy, high intensity focused ultrasound (HIFU) has attracted more and more attention in the field of hyperthermia. However, with the development of high intensity focused ultrasound (HIFU), it is found that in the process of ultrasonic hyperthermia, the theory on how to improve the cure success rate and therapeutic efficiency of ultrasonic hyperthermia is not mature. The problems related to the determination of the anatomical position and geometric shape of the therapeutic target, the determination of the therapeutic heat dose, the optimal acoustic focus distribution or the optimal scanning route and scanning speed, the calculation of the temperature distribution in the treatment area, The comparison between the calculated results of the hot zone and the predetermined heating index and the optimization of the heating method. Therefore, in order to perfect the theory of ultrasonic heating, a lot of research and exploration are needed. In this paper, the factors that influence the distribution of heat source and temperature in biological soft tissue during ultrasonic hyperthermia are discussed by numerical simulation. The main work and related conclusions are as follows: (1) the basic principle of ultrasonic hyperthermia is expounded. In this paper, the mechanism of focused ultrasound on substances in its sound field is introduced in detail, and several common medical focused sound fields are summarized. (2) several biological heat conduction models are compared. Pennes biological heat conduction model is an ideal model at present. On the basis of this model, the distribution of internal heat source is determined by the following parameters: the frequency of sound source f, the radius of curvature of transducer R and the radius of aperture a for the same biological soft tissue by using Matlab mathematical tools. The distribution of heat source is determined by the following parameters: the frequency of sound source f, the radius of curvature of transducer R and the radius of aperture a. The numerical simulation results show that the distribution of heat source in the biological tissue in the focused sound field increases with the increase of ultrasonic frequency, and the aperture radius of the transducer increases. The curvature radius of transducer becomes smaller and smaller. (3) the influence of sound source parameters and biological tissue parameters on tissue temperature distribution is analyzed. The Pennes biothermic conduction equation is solved by using the pdetool tool of Matlab. The results are as follows: a. The influence of sound source parameters on temperature rise of biological tissue. The smaller the curvature radius of transducer, the larger the aperture radius. The higher the frequency of ultrasound, the faster and more the temperature in the tissue rises. The effect of geometric focal length and transducer radius on the speed and size of temperature rise is very prominent; the higher the ultrasonic frequency, the more attenuation, The rate and magnitude of the temperature rise at the acoustic focus are smaller with the frequency. B. the larger the attenuation coefficient of the effect of biological tissue characteristic parameters on the temperature rise of the tissue, The smaller the heat conductivity is, the faster the temperature in the tissue rises. When the attenuation coefficient is larger, the change of attenuation coefficient has a relatively small effect on the temperature rise rate and magnitude at the acoustic focal point, and when the heat conduction coefficient is larger, the temperature rise is smaller, but the heating time required to reach the steady state temperature is also shorter.
【学位授予单位】：陕西师范大学
【学位级别】：硕士
【学位授予年份】：2007
【分类号】：R312

【引证文献】