【作者】 刘鹏飞；

【导师】 段会龙；

【作者基本信息】 浙江大学 ， 生物医学工程， 2012， 博士

【摘要】 心房颤动是最常见的心律失常病症,其发病率随着年龄增加而升高,其严重并持久的并发症严重威胁着人类健康。目前,导管射频消融技术在房颤的治疗中得到了广泛的应用,其原理是利用射频电流的热效应使电极接触部位生物组织变性失活从而切断异常电兴奋的传导路径。射频消融治疗的损伤区域(又称为毁损灶)尺寸是评估消融效果最重要的指标,利用有限元仿真方法对房颤导管射频消融治疗进行仿真计算温度分布和损伤区域尺寸是当前研究的热点,其对手术规划和设备制造都有重要意义。本论文利用有限元建模方法对心脏房颤导管射频消融的损伤区域尺寸进行仿真研究,全面分析影响消融损伤结果的各种因素,然后从热力学方程角度进行探讨,首次引入双曲线(Hyperbolic)热传递方程进行仿真,紧接着针对心脏的几何结构,提出新的特异性建模方法,最后,将本文的仿真结果与已有的平台实验结果进行对比验证。本论文的研究工作,为实现实际临床可用的射频消融仿真平台提供了一套方法,并为进一步的研究提供了参考。本论文主要开展了以下研究工作：论文首先详细介绍了房颤的发生机制、临床危害以及治疗方案,并描述了导管射频消融治疗房颤的机理、设备及手术过程。此外,论文系统地回顾了国内外心脏射频消融仿真工作的历史及现状,并深入分析了当前研究的热点及存在的问题。基于威斯康星大学麦迪逊分校John G. Webster小组建立的射频消融模型,论文建立了圆柱形的有限元仿真模型,并利用Pennes热力学方程进行了仿真研究。在此基础上,论文选择适当的射频消融损伤区域测量标准,并系统地分析了影响消融结果的因素,如模型尺寸,消融时间、施加电压、对流系数、电极接触状态和组织材质属性等。目前绝大多数研究都是采用傅立叶热传递公式推导而来的Pennes方程,但傅立叶热传递公式是宏观连续意义上的现象学定律,没有考虑实际情况下热量传播速度的影响,对于快速加热过程并不完全适用。针对这一问题,论文全面探讨了心脏射频消融模型适用的热力学方程,并首次引入了从非傅立叶热传递公式出发推导得出的双曲线(Hyperbolic)方程,该方程能够有效地反映心脏消融过程中热量传播实际情况。在此基础上,论文对心脏射频消融模型分别用Pennes方程和Hyperbolic方程进行仿真对照。通过对比两种方程的仿真结果,发现在射频消融的某些时间段,两种方法得到的消融损伤区域的面积差异能够达到20%。理论和实验表明,应用Hyperbolic方法能够更好的模拟心脏射频消融中的热量传递过程。为了更真实准确地模拟心脏射频消融手术的实际情况,论文提出了一种基于心脏真实解剖结构的建模方案。该方案利用真实病人的CT心脏数据,通过设定不同的电极消融场景,建立特异性的消融模型。在此基础上,论文通过综合使用MATLAB和COMSOL进行相应的有限元仿真,并与基于常规模型的仿真进行比较分析。实验结果发现,由于心脏各处几何结构的差异以及导管与心脏表面接触方式的不同,仿真获得的损伤区域存在显著的不同。此外,仿真获得的损伤区域不再是各向同性的简单形状,这反映了真实心脏解剖结构的不规则性。论文提出的这种新的建模方法为建立真正临床可用的消融仿真平台奠定了基础。论文最后将本文的仿真结果与荷兰埃因霍温理工大学Sytske Foppen在2009年进行的平台实验结果进行了对比,结果表明两者之间具有很好的吻合度,从而验证了本文提出的建模方法和仿真方法的有效性和准确性,也表明了基于真实解剖解剖的建模有可能获得更为准确的仿真结果。更多还原

【Abstract】 Atrial Fibrillation (AF) is the most common cardiac arrhythmia and its prevalence in a statistical population increases with age. Its persistent significant symptoms are very dangerous to people health. Catheter radiofrequency ablation (RFA) is now widely applied in clinic as a therapy for AF. Electric current from RFA ablates small areas of abnormal tissue to cut the accessory pathway. The lesion size of RFA is the most important criteria to evaluate ablation result. Many studies have focused on finite element method (FEM) to calculate temperature distribution and determine lesion size during RF catheter surgery and it has great value in surgery plan and medical ablation instrument invention.In the dissertation, FEM study on lesion size is performed in cardiac RFA. and various influencing factors are evaluated, then heat transfer equations suitable for RFA procedure are investigated and hyperbolic heat equation is applied to the model for the first time, furthermore a novel method is proposed to create specified ablation model based on heart anatomy, finally the modeling method is validated with published platform experiment result. The research in the dissertation proposes a method to develop RFA simulation platform in clinic and provides a reference for further study.The main content of the dissertation is followings:AF disease is introduced including its cause, signs, symptoms and therapy guidelines, and then cardiac catheter RFA is presented such as physical mechanism, instruments and surgery procedure. At last, recent progress in related FEM research on lesion size estimation is reviewed systematically and hot research topics are discussed.A3D cylinder ablation model is created based on the research by the John G. Webster group in University of Wisconsin-Madison. Pennes heat transfer equation is adopted to perform FEM simulation and the lesion size determination criteria is studied. Furthermore, lesion size influencing factors are evaluated one by one, such as model radius, ablation duration, voltage, convective coefficients, electrode contact status and tissue physical properties, etc. Most of studies adopt Pennes heat equation which is derived from Fourier theory. Fourier theory is based on macroscopical phenomenon and it doesn’t consider heat wave propaganda speed, so it is not suitable for rapid heating procedure. In the dissertation, study is performed on the heat transfer equations suitable for RFA procedure and hyperbolic heat equation derived from Non-Fourier heat theory is applied and it takes the thermal wave behavior into account. In RFA model, FEM is adopted to study the model with corresponding Pennes heat equation and hyperbolic heat equation. Different convection coefficients and voltages are applied to simulate different conditions. The results show that the lesion size difference ratio can reach20%in some periods of ablation. The difference is significant and the methodological study shows that hyperbolic method is more suitable for RFA model.In order to simulate ablation for actual surgery procedure, a novel method is proposed to create specified ablation model suitable for heart anatomy. FEM analysis study is performed based on cardiac CT data. At first, one detailed cardiac ablation model is created with CT heart inner surface mesh, and various electrode contact status can be specified by user selection. Then COMSOL scripts were called by MATLAB to perform FEM analysis. The temperature profile and ablation lesion size are estimated after simulation. It shows that ablation results vary obviously with electrode insertion angles and penetration depths. Besides, the lesion region shape is not isotropy due to complex and atactic heart chamber anatomy. The method lays the foundation of the RFA simulation platform in clinic.Finally, a comparison is carried out between the model in the dissertation with the published platform experiment result by Sytske Foppen in Eindhoven University of Technology,2009. It shows that simulation result is consistent with that of the experiment. It validates the modelling method and indicates that the specified model based on heart anatomy will make results more precise.更多还原