高强度聚焦超声治疗声场和温度场控制方法研究

发布时间：2018-12-19 20:22

【摘要】：高强度聚焦超声(HIFU)治疗目前已经被成功地用于多种肿瘤治疗之中。其原理是：运用超声换能器将声能汇聚到生物体肿瘤所在区域,通过各种效应,尤其是热效应,使该区域肿瘤细胞发生蛋白质变性,且尽可能不损伤周边正常组织,从而达到治疗目的。在临床应中,由于延时、超调、振荡、用时过长等原因,皮肤烧伤、钙化、治疗不彻底、神经损伤等问题时有出现,因此治疗目标区域的声强和温度控制非常重要。本文以生物热传导模型为基础,对不同换能器在生物组织中产生的声场和温度场进行了仿真,分析了各种参数对声聚焦的影响,并提出了温度控制方法。所做工作如下： 1.建立生物组织模型,研究了生物热传导问题、聚焦声场的计算方法和模糊控制有关理论。 2.研究了凹球面换能器在单层和多层生物媒质中产生的声场,分析了声源及组织参数对声场影响。结果表明：声速越大或频率越低,其最大声压值越大、焦距越短；初始声压越大或吸收系数越小,其最大声压值越大、焦距几乎不变；多层媒质中某层厚度的变化对焦域最大声压值有一定的影响。 3.运用伪逆算法研究了相控阵换能器在生物媒质中实现聚焦时的声场,分析了不同参数对声场特征的影响。结果表明：换能器阵元间距变大或者阵元宽度变小,焦点处声压会变小；换能器频率不同时,不能采用相同信号进行驱动；生物媒质参数相差较大时,其焦域面积也相差较大；某层的吸收系数或厚度发生变化时,其焦点声压会受到影响；通过改变阵元驱动信号,换能器能形成多个焦点,适用于治疗大肿瘤。 4.将模糊控制方法用于HIFU治疗时温度控制,研究了凹球面换能器加热单层媒质和多层媒质时温度控制效果,及相控阵换能器加热时单点和多点温度控制效果,并与传统PID控制进行了比较。结果表明模糊控制优于传统PID控制,避免了传统控制中出现的延时、超调、振荡、用时过长等问题。本文做了大量的仿真研究,分析得出了不同参数对声场的影响以及声场优化方法；在HIFU加热治疗中提出了模糊控制方法,能有效提高治疗的安全性和效率。所做工作对HIFU治疗应用有重要意义,其结果对治疗剂量选取有参考价值。
[Abstract]:High intensity focused ultrasound (HIFU) therapy has been successfully used in many kinds of tumor therapy. The principle is that ultrasonic transducers are used to gather sound energy into the area where the tumor is located, and through various effects, especially the thermal effect, the tumor cells in the region undergo protein denaturation without damaging the surrounding normal tissue as much as possible. So as to achieve the purpose of treatment. In clinical practice, due to the causes of delay, overshoot, oscillation, prolonged use, skin burn, calcification, incomplete treatment, nerve injury and so on, it is very important to control the sound intensity and temperature of the target area. Based on the biological heat conduction model, the sound field and temperature field produced by different transducers in biological tissues are simulated, the influence of various parameters on acoustic focusing is analyzed, and a temperature control method is proposed. The work done is as follows: 1. The biological tissue model is established, the biological heat conduction problem, the calculation method of focused sound field and the theory of fuzzy control are studied. 2. The sound field produced by concave spherical transducer in single-layer and multi-layer biological media is studied. The influence of sound source and structure parameters on sound field is analyzed. The results show that the larger the sound velocity or the lower the frequency, the greater the maximum sound pressure and the shorter the focal length, the larger the initial sound pressure or the smaller the absorption coefficient, the greater the maximum sound pressure and the focal length. The variation of the thickness of a certain layer in multilayer medium has a certain influence on the maximum sound pressure in focal region. 3. The sound field of phased array transducer focusing in biological medium is studied by using pseudo-inverse algorithm, and the influence of different parameters on sound field characteristics is analyzed. The results show that the distance between the array elements of the transducer becomes larger or the width of the array becomes smaller, the sound pressure at the focal point becomes smaller, the frequency of the transducer is different, the same signal can not be used to drive the transducer, and the focal area of the transducer varies greatly when the parameters of biological medium differ greatly. When the absorption coefficient or thickness of a certain layer changes, the focus sound pressure will be affected, and by changing the driving signal of the array element, the transducer can form multiple focal points, which is suitable for the treatment of large tumors. 4. The fuzzy control method is applied to the temperature control of HIFU treatment. The effect of temperature control on single layer and multi layer media heated by concave spherical transducer and single and multi point temperature control effect on phase array transducer heating is studied. And compared with the traditional PID control. The results show that the fuzzy control is superior to the traditional PID control, and avoids the problems of delay, overshoot, oscillation and long time in the traditional control. In this paper, the influence of different parameters on the sound field and the sound field optimization method are analyzed, and the fuzzy control method is put forward in the HIFU heating therapy, which can effectively improve the safety and efficiency of the treatment. The results are of great significance to the application of HIFU, and the results are of reference value to the selection of therapeutic dose.
【学位授予单位】：湖南师范大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TB553;R730.5

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