Mathematical modeling of impedance controlled radiofrequency tumor ablation and ex-vivo validation

Radiofrequency (RF) ablation uses RF current to heat and kill cancer applied via an electrode inserted under image-guidance, and is in clinical use for tumors in liver, lung kidney, and bone. Mathematical models are frequently used to determine tissue temperature during RF ablation, but most prior models do not include accurate implementation of power control algorithms as are used in clinical devices. We created a computer model employing the Finite Element Method, and implemented a clinically used impedance control algorithm. We assumed a rapid increase in tissue electrical conductivity upon vaporization to approximate tissue vapor formation and allow impedance control. We performed ex vivo tissue experiments where we measured the tissue temperature and impedance to validate the computer models. Impedance and temperature time course were comparable between model and experiments, and deviations are likely due to inaccurate data on temperature dependence of tissue properties. Ablation zone diameter was 33 mm in the computer model, and 29 ± 3 mm in the experiments. Our computer model may more accurately allow tissue temperature calculation via including power control algorithms as used in clinical devices.