低温手术过程多维传热有限元分析

Finite Element Analysis of Multidimensional Heat Transfer during Cryosurgery

目的通过有限元分析,给出低温手术过程组织三维瞬态温度场;考察人体血液灌注和代谢产热对其影响,为优化设计冷刀提供参考。方法充分考虑组织物性和内热源的非线性,使用基于有限容积法的大型商业有限元软件Ansys求解描述低温手术过程组织传热问题的经典生物传热方程。结果考虑血液灌注和代谢产热后,组织局部降/复温速率降低、所经历的最低温度绝对数值减少;对应时刻,组织内局部温度梯度增加;相同手术方案下,组织内冻结区域减小,且冰球生长过程减慢。结论人体血液灌注和代谢产热对低温手术过程影响显著,体外实验由于无法模拟血液灌注和代谢产热效果而对冷刀的优化设计作用有限,必须进行在体实验以优化冷刀及其相应的低温手术方案。

Objective To study the effect of blood flow and metabolism on the transient thermal field of the target tissue, and to evaluate the efficiency of in vitro experiments for optimizing the design of cryoprobe. Method The enthalpy form of the classical bioheat equation was solved by using commercial software Ansys （version 7.0）. The tissue was treated as nonideal materials, freezing over a temperature range, and the thermophysical properties of which were temperature dependent. Result Due to the heating effect of the blood flow and metabolism, the local cooling rate of the target tissue was apparently decreased, and the thermal gradient changed more acutely, the propagation rate of the freezing front was slowed down and the maximal radius of the ice ball was also decreased. Conclusion The heat source term caused by blood flow and metabolism in the bioheat transfer equation has much influence on the transient thermal and thermal gradient fields of the target tissues. In vitro experiments can not be used to fully optimize the design of cryosurgery, corresponding in vivo experiments are needed.