【作者】 吴立顺；

【导师】 菅喜岐；

【作者基本信息】 天津医科大学 ， 生物医学工程， 2008， 硕士

【摘要】 目的:高强度聚焦超声(High Intensity Focused Ultrasound,HIFU)肿瘤治疗技术是超声换能器发出的超声波,在超声聚焦装置的作用下形成高强度超声能量的焦点区域,使肿瘤组织吸收焦点区域高强度超声能量,在短时间内温度升到60℃以上(60℃以上的焦点区域称为可治疗焦域)而发生凝固性坏死的治疗技术。该技术因具有有效、微创伤、能量深入深部组织等优点,成为众多研究者关注和研究的热点并应用于临床肿瘤治疗中。现有的HIFU肿瘤治疗系统对于焦点区域温度的监控以及治疗效果的实时检测问题都没有得到很好的解决,使HIFU肿瘤治疗系统的可靠性和安全性不能保障,临床治疗中常出现皮肤烧伤、神经损伤、靶区肿瘤组织残留等并发症,极大地限制了HIFU肿瘤治疗系统的应用。本论文通过数值仿真高强度聚焦超声传播过程中温度场的变化,研究不同换能器阵元激励函数、不同治疗剂量以及生物组织血流灌注对焦点区域温度场、焦点区域位置、形状和大小等的影响,为高强度聚焦超声肿瘤治疗临床治疗可靠性提高,治疗计划制定提供技术参数和技术方法。方法:本研究基于森田长吉等人提出的高强度超声波非线性传播时域有限差分仿真法之上,结合Pennes热传导方程提出了人体组织内温度分布的时域有限差分仿真方法;并以人体乳房为例建立三维数值仿真模型,进行数值仿真人体乳房组织内高强度聚焦超声非线性传播过程中组织的温度分布。结果:仿真结果表明高强度聚焦超声肿瘤治疗过程中,经过单次照射后,随着超声波的聚焦传播,焦点区域组织温度不断上升,最后维持一定的温度值不变化;皮肤组织温升比皮下脂肪组织和水体温升高;聚焦形成的实际焦距与设备的几何焦距有一定的差异。在换能器工作频率、平均输入声强和连续照射时间相同而阵元激励函数不同条件下,水、皮肤和表浅脂肪组织中形成温度分布基本相同,而在焦点区域明显不同;换能器工作频率、平均输入声强及连续照射时间等不同治疗剂量的选择均会导致皮肤及焦点区域各处温度场的变化;生物组织的血流灌注对HIFU焦区温度的温升和形成焦点区域的大小、位置亦有较大的影响。结论:本论文以乳房为例建立三维数值仿真模型,并利用FDTD仿真方法研究高强度聚焦超声温度场变化以及不同阵元激励函数、不同治疗剂量以及生物组织血流灌注对高强度聚焦超声焦点区域温度场的影响。结论如下:(1)对于压电陶瓷阵元,整合层的加入与否,一般不会改变60℃以上可治疗区域的大小。但是加入整合层后,焦点区域中心温度低于未加整合层时的焦点区域中心温度。皮肤处温度基本相同。(2)在相同输入声强和照射时间条件下,随着频率的增高,焦距变小,60℃以上可治疗区体积变小,焦区最高温度升高的同时皮肤处的温度也升高,40℃～45℃的区域相应增大。(3)当频率和照射时间一定时,随着输入声强的增加,可治疗焦区的体积增大,40℃～60℃的区域也增大,皮肤处的温度明显升高;同时皮肤处40℃～45℃的区域由声轴向两边扩展,面积增大。但焦距保持不变。(4)在相同频率和输入声强的条件下,随着照射时间的增加,可治疗焦点区域的体积增大,40℃～45℃的区域也明显增大,焦区中心温度升高。皮肤处的温度略有升高。焦距随照射时间的增加几乎不改变。(5)在治疗剂量相同条件下,有血流灌注的活体内形成的可治疗区域体积略小于无血流灌注的离体组织内的焦域体积。但活体组织内中心温度高于离体组织,形成焦距也略小于离体组织。更多还原

【Abstract】 Objective:High Intensity Focused Ultrasound(HIFU)tumor therapy is a promising technique that uses high intensity ultrasound to destroy tissues in a confined region which will avoid traditional invasive methods.It features the application of HIFU, high local temperatures of above 60℃and short treating time of a few seconds.It has been widely used due to its effective,micro-impassivity and deep into human tissues’ advantages.Application of this technique may spare patients from ionizing radiation, chemical reactions and poison-minus effect.But it is difficult for existing HIFU tumor therapy system to monitor the focal region temperature in real-time accurately and objectively and predict the shape and size of the focal region.So complications such as skin burn,damage of overlying tissues and residual of target tumor may occur.In order to avoid these clinical complications,it is very necessary to investigate the focal region temperature in human tissues and predict different factors that effect on HIFU temperature field.Methods:In this work,FDTD method which was proposed by Nagayoshi Morita to simulate pressure,velocity of nonlinear propagation high intensity ultrasound, together with Pennes bio-heat transfer equation are applied to simulate temperature field in a 3-D cylinder coordinate which is established referring to human brests, temperature distribution of different propagation time is simulated.Result:The simulation results display that the temperature of focal region is in human tissues increase when heating time becomes longer.Then,it keeps invariab in a short time.The focal length produced by HIFU propagation is different with HIFU geometric focal length.The temperature distribution are the same in skin and slight fat with different excitation function,but different in focal area.Different choice of ultrsound dosage will lead to the changes of temperature field.Blood perfusion has an important influence on HIFU temperature field.Conclusion:This work simulate temperature field in HIFU.3-D cylinder coordinate is established referring to human brests and FDTD method is used to calculate temperature field numerically.The conclusion are as follow:(1)add integrated layer or not will take little influence on the distribution of HIFU temperature field.But without the integrated layer,the central temperature of focal region will be higher.(2)With the same ultrasound power densities and exposure time,When the frequency becomes higher,the skin temperature on the center becomes higher than slight fat,the area of focal region decreases,the focal length shortens,and a slightly increased skin temperature on the center is observed.(3)As the frequency and exposure time are the same,when ultrasound power densities becomes higher,the area of focal region increases but the focal length does not change very much.The temperature of skin increased dramatically due to higher ultrasound power densities.(4)With the same frequency and ultrasound power densities,when exposure time becomes higher,the area of focal region increases but the focal length does not change very much.The temperature of skin increased.(5)When the Ultrasound dosage are same,the area of focal region and focal lenth will decrease but central temperature will be higher with blood perfusion.更多还原