Karaki Wafaa, Lopez Carlos A, Borca-Tasciuc Diana-Andra, De Suvranu
Center for Modeling, Simulation and Imaging in Medicine, Rensselaer Polytechnic Institute, Troy, NY, USA.
Int J Heat Mass Transf. 2018 Dec;127(Pt A):961-974. doi: 10.1016/j.ijheatmasstransfer.2018.07.006. Epub 2018 Jul 14.
Radio-frequency (RF) heating of soft biological tissues during electrosurgical procedures is a fast process that involves phase change through evaporation and transport of intra- and extra-cellular water, and where variations in physical properties with temperature and water content play significant role. Accurately predicting and capturing these effects would improve the modeling of temperature change in the tissue allowing the development of improved instrument design and better understanding of tissue damage and necrosis. Previous models based on the Pennes' bioheat model neglect both evaporation and transport or consider evaporation through numerical correlations, however, do not account for changes in physical properties due to mass transport or phase change, nor capture the pressure increase due to evaporation within the tissue. While a porous media approach can capture the effects of evaporation, transport, pressure and changes in physical properties, the model assumes free diffusion of liquid and gas without a careful examination of assumptions on transport parameters in intact tissue resulting in significant under prediction of temperature. These different approaches have therefore been associated with errors in temperature prediction exceeding 20% when compared to experiments due to inaccuracies in capturing the effects of evaporation losses and transport. Here, we present a model of RF heating of hydrated soft tissue based on mixture theory where the multiphase nature of tissue is captured within a continuum thermomechanics framework, simultaneously considering the transport, deformation and phase change losses due to evaporation that occur during electrosurgical heating. The model predictions are validated against data obtained for ablation of porcine liver tissue at various power settings of the electrosurgical unit. The model is able to match the mean experimental temperature data with sharp gradients in the vicinity of the electrode during rapid low and high power ablation procedures with errors less than 7.9%. Additionally, the model is able to capture fast vaporization losses and the corresponding increase in pressure due to vapor buildup which have a significant effect on temperature prediction beyond 100 °C.
在电外科手术过程中，对柔软生物组织进行射频（RF）加热是一个快速过程，该过程涉及通过细胞内和细胞外水分的蒸发及传输实现的相变，且物理性质随温度和含水量的变化起着重要作用。准确预测和捕捉这些效应将改进组织温度变化的建模，从而有助于开发改进的器械设计，并更好地理解组织损伤和坏死情况。以往基于彭尼斯生物热模型的模型既忽略了蒸发和传输，又或者通过数值关联来考虑蒸发，但没有考虑由于质量传输或相变导致的物理性质变化，也没有捕捉到组织内由于蒸发引起的压力增加。虽然多孔介质方法可以捕捉蒸发、传输、压力和物理性质变化的影响，但该模型假定液体和气体自由扩散，而没有仔细研究完整组织中传输参数的假设，导致温度预测明显偏低。因此，与实验相比，这些不同的方法在温度预测上存在超过20%的误差，原因在于捕捉蒸发损失和传输效应时不够准确。在此，我们基于混合物理论提出了一种水合软组织的射频加热模型，该模型在连续介质热力学框架内捕捉组织的多相性质，同时考虑了电外科加热过程中由于蒸发而产生的传输、变形和相变损失。针对在电外科设备的各种功率设置下对猪肝组织进行消融所获得的数据，对模型预测进行了验证。在快速低功率和高功率消融过程中，该模型能够将平均实验温度数据与电极附近的陡峭梯度相匹配，误差小于7.9%。此外，该模型能够捕捉快速的汽化损失以及由于蒸汽积聚导致的相应压力增加，而这对超过100°C的温度预测有显著影响。
