Abstract
The character of ablation processes with high-frequency electrical current is similar in most biological tissues; however, quantitative characteristics are very different. Consequently, mathematical models of the process have a lot of specific aspects. In this study, we developed mathematical model of radiofrequency ablation in liver tissues with experimental validation of model in ex vivo porcine liver. The finite element nonlinear computational model for the simulation of the radiofrequency ablation processes and taking into account coupled electrical and thermal phenomena has been developed. The radiofrequency electric current processes are dominated by the active electric conductivity. The heat generation in biological tissues is determined by the electric current density. Simultaneously, the conductivity of the tissue is nonlinearly dependent upon the temperature of the tissue. The model has been implemented in COMSOL Multiphysics computational environment. Tests on physical characteristics of the thermal effect in ex vivo liver tissue have been performed and results compared. Two oval-shaped zones of total and relative tissue destruction were highlighted. The principal distribution of the thermal effect is congruous with the theoretical model; however, the discrepancy of temperatures in experimental and theoretical models increases distally from active perfusion electrode. Distribution of the thermal effect is congruous in the theoretical and experimental model; however, discrepancies of temperatures imply certain inadequacies of the mathematical models. Differences of computed and actual temperatures should be regarded predicting tissue ablation in clinical setting.
Highlights
Several kinds of tissue ablation by means of highfrequency electrical currents are employed in biomedical practice
Numerical results Investigation of the steady electro-thermal RF ablation process Here we investigate a balanced heat exchange process, which could be obtained if the electric current flows through tissues for a very long time
Such values are obtained after about 20 min of Radiofrequency ablation (RFA), when the measured temperature values do not change in time any more
Summary
Several kinds of tissue ablation by means of highfrequency electrical currents are employed in biomedical practice. Radiofrequency ablation (RFA) is a new local thermal ablative technique for the treatment of unresectable hepatic tumors including hepatocellular carcinoma (2). The basic physical processes taking place during RFA are electrical current flowing in the tissue and causing volumetric heat generation, as well as heat exchange in thermally conductive tissues. The analysis can be reasonably simplified by assuming the quasi-static model of Investigation of radiofrequency ablation process by finite element modeling and experiment 311 electrical conductance. This implies the consideration of alternating voltage and electrical current in terms of their effective values obtained by solving the equations of direct current in conductive media. The lesion of the tissue as a consequence of heating can be evaluated by using the Arrhenius formula (7)
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