Comparison of Enthalpy Method and Water Fraction Method to Mathematically Model Water Vaporization During RF Ablation

[EN] During high-temperature energy-based therapies such as radiofrequency ablation (RFA) the target tissue temperatures around 100ºC, which causes tissue dehydration by water vaporization. In order to be as realistic possible, RFA theoretical models should include the formulation of these phenomena. There are currently two fixed methods of modeling the electrical and thermal effects produced by water vaporization: the enthalpy method and water fraction method. Our objective was to compare both methods, especially to assess the thermal and electrical in terms of electrical impedance progress during heating, distributions of temperature, and temperature at some specific locations. The results showed the performance of both methods to be qualitatively analogous, similar impedance progress, temperature distributions and temperature progress. They were hence equally able to the thermal and electrical performance in a pulsed protocol, i.e. during the period without applying RF power. The difference between the methods was the time at which impedance started to rise. All these findings suggest that two methods offer equivalent results in RFA modeling. However, since the enthalpy method has one less problem to solved (dynamic volume fraction of liquid water in the tissue) it is less complex, has a lower computational cost and seems to be more suitable for modeling RFA with dry or internally cooled electrodes, i.e. those in which there is interstitial saline infusion. However, the water fraction method would be more appropriate in the case of RFA with irrigated electrodes.