Numerical evaluation of ablation zone under different tip temperatures during radiofrequency ablation

The present study aimed at investigating the relationship between the shape and size of ablation zone and the ablation time during radiofrequency ablation (RFA) at different tip temperatures (80, 85, 90, and 95 °C). A two-dimensional simulation model of liver RFA using single-electrode was first built by finite element method (FEM). A closed-loop proportional-integral (PI) controller was employed in the FEM model. The heat transfer issues were solved based on Pennes biological equation. To improve simulation accuracy of the FEM models, temperature-dependent forms of the electrical conductivity and the thermal conductivity were adopted in the model. The ablation zone was assessed by 54 °C isothermal contour (IT54). The ablation zone sizes obtained from the numerical simulations and ex vivo experiments were compared to evaluate the validity of the numerical model. All the four tip temperatures (80, 85, 90, and 95 °C) were tested using 3 ex vivo porcine livers respectively. According to numerical simulation results, the characterization functions of the ablation volume and the ablative margin (AM) were derived. The proposed curve functions could precisely characterize the shape and size of ablation zone at different preset tip values, and the statistical results showed that the prediction curves had a good consistency with simulation curves. This paper proposed the prediction models of the ablation zone in the RFA process, which could be used to achieve accurate planning of RFA needle placements and optimize patient care during temperature-controlled RFA therapy.