Numerical simulation of the microwave rewarming process of cryopreserved organs

The rewarming process of cryopreserved organs using microwave technology is analyzed by numerical simulation. The FDTD finite-difference time-domain) method is applied to calculate the electromagnetic field in a real microwave rewarming system, composed by a cylindrical resonant cavity, an antenna source, and a frozen rabbit-kidney phantom with temperature-dependent properties. The efficiency of the FDTD codes is improved by nonuniform grid techniques and parallel algorithms. Meanwhile, an apparent specific-heat method is introduced in the temperature-field calculation. Coupling the solutions of the two fields is realized by a formerly developed algorithm. The numerical results show that in the rewarming process of the rabbit kidney phantom, the warming rate can reach 300°-500°C/min, which may prevent devitrification, but the maximum temperature difference in the sample (18 mm in radius) can reach 15°C at the end, which may cause severe thermal stress.