Schutt David J, Haemmerich Dieter
Department of Pediatrics, Medical University of South Carolina, Charleston, South Carolina 29425, USA.
Med Phys. 2008 Aug;35(8):3462-70. doi: 10.1118/1.2948388.
Finite element method (FEM) models are commonly used to simulate radio frequency (RF) tumor ablation. Prior FEM models of RF ablation have either ignored the temperature dependent effect of microvascular perfusion, or implemented the effect using simplified algorithms to reduce computational complexity. In this FEM modeling study, the authors compared the effect of different microvascular perfusion algorithms on ablation zone dimensions with two commercial RF electrodes in hepatic tissue. They also examine the effect of tissue type and inter-patient variation of perfusion on ablation zone dimensions.
The authors created FEM models of an internally cooled and multi-tined expandable electrode. RF voltage was applied to both electrodes (for 12 or 15 min, respectively) such that the maximum temperature in the model was 105 degrees C. Temperature dependent microvascular perfusion was implemented using three previously reported methodologies: cessation above 60 degrees C, a standard first-order Arrhenius model with decreasing perfusion with increasing degree of vascular stasis, and an Arrhenius model that included the effects of increasing perfusion at the ablation zone boundary due to hyperemia. To examine the effects of interpatient variation, simulations were performed with base line and +/-1 standard deviation values of perfusion. The base line perfusion was also varied to simulate the difference between normal and cirrhotic liver tissue.
The ablation zone volumes with the cessation above 60 degrees C perfusion algorithm and with the more complex Arrhenius model were up to 70% and 25% smaller, respectively, compared to the standard Arrhenius model. Ablation zone volumes were up to 175% and approximately 100% different between the simulations where -1 and +1 standard deviation values of perfusion were used in normal and cirrhotic liver tissue, respectively.
The choice of microvascular perfusion algorithm has significant effects on final ablation zone dimensions in FEM models of RF ablation. The authors also found that both interpatient variation in base line tissue perfusion and the reduction in perfusion due to cirrhosis have considerable effect on ablation zone dimensions.
有限元法（FEM）模型常用于模拟射频（RF）肿瘤消融。先前的射频消融有限元模型要么忽略了微血管灌注的温度依赖性效应，要么采用简化算法来实现该效应以降低计算复杂度。在这项有限元建模研究中，作者比较了不同微血管灌注算法对肝组织中两种商用射频电极消融区尺寸的影响。他们还研究了组织类型和患者间灌注差异对消融区尺寸的影响。
作者创建了一个内部冷却且多针可扩张电极的有限元模型。对两个电极分别施加射频电压（分别为12或15分钟），使模型中的最高温度达到105摄氏度。使用三种先前报道的方法来实现温度依赖性微血管灌注：60摄氏度以上停止灌注、随着血管淤滞程度增加灌注减少的标准一阶阿伦尼乌斯模型，以及一个考虑到由于充血导致消融区边界灌注增加的阿伦尼乌斯模型。为了研究患者间差异的影响，使用灌注的基线值以及±1标准差进行模拟。还改变基线灌注以模拟正常和肝硬化肝组织之间的差异。
与标准阿伦尼乌斯模型相比，60摄氏度以上停止灌注算法和更复杂的阿伦尼乌斯模型的消融区体积分别小70%和25%。在正常和肝硬化肝组织中分别使用灌注的-1和+1标准差进行模拟时，消融区体积差异分别高达175%和约100%。
微血管灌注算法的选择对射频消融有限元模型中最终消融区尺寸有显著影响。作者还发现，患者间基线组织灌注差异以及肝硬化导致的灌注减少对消融区尺寸有相当大的影响。
