高强度聚焦超声非线性声场和组织损伤形成的扫描模式比较研究

发布时间：2018-03-09 04:01

  本文选题：高强度聚焦超声　切入点：非线性声场　出处：《南京大学》2012年博士论文　论文类型：学位论文

【摘要】：高强度聚焦超声(HIFU)技术将声能量聚焦至靶区,热消融肿瘤组织而不损伤周围正常组织。作为一种新兴的非侵入式治疗肿瘤方法,近年来,HIFU得到了人们极大的关注。本论文的工作主要有两方面的内容：(1)声透镜聚焦换能器的非线性声传播模型,(2)HIFU治疗中组织损伤形成的扫描方式比较。 声透镜式聚焦换能器是常用的声聚焦方式之一。文中提出了一种计算大张角强聚焦的声透镜式聚焦换能器的非线性声场分布模型。在此模型中,我们使用虚拟球壳式声源边界条件来代替声透镜边界条件,虚拟声源的几何焦距和孔径大小先由Snell折射定律确定,再结合Rayleigh积分线性声场结果微调；然后根据SBE模型,计算声源的非线性声场分布。按照此模型计算焦点声强为7.0kW/cm2时的非线性声场分布,并与Westervelt方程和KZK方程计算结果相比较；结果表明,此模型能准确的描述焦域附近的非线性声场分布；对于声场近场区域,此模型的计算结果与Rayleigh积分结果以及Westervelt方程结果差异较大。此外,该模型的数值计算时间约为使用有限差分法计算Westervelt方程所需时间的1/10 HIFU治疗较大体积的肿瘤时,换能器需要以一定的扫描模式运动,常用的运动方式有离散序列扫描和连续扫描两种。我们将理论建模和实验结合,比较了这两种扫描方式下的温度场和损伤分布。在半透明仿生凝胶中进行实验研究,声功率75W,频率1.12MHz,换能器以不同的扫描速度移动,观察损伤分布。理论模型中,利用KZK方程描述非线性声束传播,利用Pennes传热方程描述组织中的温度变化。理论和实验结果表明,离散序列扫描模式下,相邻点间隔增加时,峰值温度和损伤分布轮廓呈现出锯齿状；连续扫描模式下,峰值温度和损伤分布的边界比较光滑；提高扫描速度后,峰值温度明显降低。通过控制扫描速度可以控制峰值温度和损伤分布,这有助于进一步提高HIFU治疗效率。此外,和离散序列扫描模式相比,连续扫描可以在较低的峰值温度下,达到较高的损伤形成效率(单位时间内形成的损伤面积)。 此外,本论文的其他工作还有：建立了一个声场、温度场和微泡相互耦合的数值模型,以研究焦点温度达到沸点后,气化微泡对声场、温度场的影响。基于SBE模型,建立强聚焦声束在多层介质中传播的非线性模型。 本论文在高强度聚焦超声的非线性声场及组织损伤形成方面的理论及实验研究工作将进一步促进高强度聚焦超声在临床上的应用。
[Abstract]:High intensity focused ultrasound (HIFU) technology focuses acoustic energy on the target area, ablation tumor tissue without damaging the surrounding normal tissue. In recent years, great attention has been paid to HIFU. In this paper, there are two main contents: 1) comparing the scanning modes of tissue injury in the treatment of HIFU with the nonlinear acoustic propagation model of lens focusing transducer. The acoustic lens focusing transducer is one of the commonly used acoustic focusing methods. In this paper, a nonlinear sound field distribution model is proposed to calculate the acoustic lens focusing transducer with large angle of tension. The boundary condition of virtual spherical shell sound source is used to replace the boundary condition of acoustic lens. The geometric focal length and aperture of virtual sound source are determined by Snell's refraction law, and then the results of Rayleigh integral linear sound field are fine-tuned, and then according to the SBE model, The nonlinear sound field distribution of the sound source is calculated. The nonlinear sound field distribution is calculated when the focal sound intensity is 7.0 kW / cm ~ 2, and compared with the results of Westervelt equation and KZK equation, the results show that, The model can accurately describe the distribution of nonlinear sound field near focal region, and for the near field of sound field, the results of the model are quite different from the results of Rayleigh integral and Westervelt equation. The numerical calculation time of the model is about 1/10 of the time required to calculate the Westervelt equation by the finite difference method. When HIFU is used to treat large volume tumors, the transducer needs to move in a certain scanning mode. There are two common motion modes: discrete sequence scanning and continuous scanning. The temperature field and damage distribution of these two scanning modes were compared. The experimental study was carried out in a translucent bionic gel. The acoustic power was 75W, the frequency was 1.12MHz, the transducer moved at different scanning speeds, and the damage distribution was observed. The KZK equation is used to describe the nonlinear acoustic beam propagation and the Pennes heat transfer equation is used to describe the temperature change in the tissue. The theoretical and experimental results show that when the interval between adjacent points increases in the discrete sequence scanning mode, The contour of peak temperature and damage distribution is serrated. In continuous scanning mode, the boundary between peak temperature and damage distribution is smooth. The peak temperature and damage distribution can be controlled by controlling the scanning speed, which is helpful to further improve the therapeutic efficiency of HIFU. In addition, compared with discrete sequence scanning mode, continuous scanning can be used at lower peak temperature. To achieve higher damage formation efficiency (damage area per unit time). In addition, the other work of this paper is to establish a numerical model of the coupling of sound field, temperature field and microbubble to study the effect of vaporizing microbubble on sound field and temperature field after the focal temperature reaches boiling point. A nonlinear model for the propagation of a strong focused sound beam in a multilayer medium is established. The theoretical and experimental research on the nonlinear sound field and tissue damage of high intensity focused ultrasound (HIFU) will further promote the clinical application of HIFU.
【学位授予单位】：南京大学
【学位级别】：博士
【学位授予年份】：2012
【分类号】：R310

【共引文献】

中国博士学位论文全文数据库 前1条

1 刘全宏;超声激活血卟啉抗肿瘤的细胞学研究[D];陕西师范大学;2003年

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