Numerical study on three-region thawing problem during cryosurgical re-warming

Knowledge of the temperature transients of biological bodies during cryosurgical re-warming is critical for the survival of healthy tissues. To better understand the mechanisms thus involved, a one-dimensional numerical algorithm based on finite difference method was applied to simultaneously solve the thawing processes occurring in three regions with one thawing, another blood-perfused and the third frozen one sandwiched between them. Two typical surface heatings with heating plate or convective warm water and a spatial heating using microwave were particularly adopted to investigate the advancement of the two phase-change interfaces and the transient temperature field over the tissue. Differences among these results were compared and their implementation for the cryosurgical re-warming were discussed. Parametric studies were performed to explore influences of the blood perfusion, the microwave heating power, the surface heat convection coefficient, and the surface heating temperature to the thermal history of the biological bodies. Taking account of several typical blood re-flow patterns most probably occurred in the originally frozen and then thawed tissues after the two phase change interfaces meet together, four heat transfer equations were proposed to characterize the re-warming behavior of the biological body. Effect of the non-ideal solution property of the living tissues to the transient temperature field during cryo-surgical re-warming was also tested through introducing a simple however intuitive way.