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 in vivo 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.

中文翻译：

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水合软生物组织体内电外科加热的连续热机械模型

电外科手术期间软生物组织的射频 (RF) 加热是一个快速过程，涉及通过蒸发和细胞内外水的运输而发生的相变，并且物理特性随温度和含水量的变化起着重要作用。准确预测和捕获这些影响将改进组织中温度变化的建模，从而允许开发改进的仪器设计并更好地了解组织损伤和坏死。基于 Pennes 生物热模型的先前模型忽略蒸发和传输，或通过数值相关性考虑蒸发，但是，没有考虑由于质量传输或相变引起的物理特性变化，也没有捕获由于组织内蒸发引起的压力增加. 虽然多孔介质方法可以捕获蒸发、传输、压力和物理特性变化的影响，但该模型假设液体和气体自由扩散，而没有仔细检查完整组织中传输参数的假设，从而导致温度预测显着不足。因此，与实验相比，由于捕捉蒸发损失和传输的影响不准确，这些不同的方法与温度预测的误差超过 20%。在这里，我们提出了一个基于混合理论的水合软组织的射频加热模型，其中组织的多相性质在连续热力学框架内被捕获，同时考虑传输，由于在电外科加热过程中发生的蒸发而导致的变形和相变损失。根据在电外科装置的各种功率设置下对猪肝组织进行体内消融获得的数据，对模型预测进行了验证。该模型能够在快速低功率和高功率消融过程中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，该模型能够捕获快速蒸发损失和由于蒸汽积聚而导致的相应压力增加，这对 100 °C 以上的温度预测具有显着影响。该模型能够在快速低功率和高功率消融过程中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，该模型能够捕获快速蒸发损失和由于蒸汽积聚而导致的相应压力增加，这对 100 °C 以上的温度预测具有显着影响。该模型能够在快速低功率和高功率消融过程中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，该模型能够捕获快速蒸发损失和由于蒸汽积聚而导致的相应压力增加，这对 100 °C 以上的温度预测具有显着影响。