Finite element modeling of cooled-tip probe radiofrequency ablation processes in liver tissue.

Finite element model of radiofrequency ablation (RFA) with cooled-tip probe in liver has been developed by employing COMSOL Multiphysics software. It describes coupled electric, thermal and sodium chloride solution infiltration flow phenomena taking place during ablation processes. Features of hydraulic capacity, saturation of the tissue by infiltration, and dependency of electrical conductivity on the damage integral of the tissue have been supplied to the model. RFA experiments have validated the model. Physical parameters describing hydraulic capacity and hydraulic conductivity in the tissue, as well as, the relation of electrical conductivity against the value of damage integral have been determined.

Finite element modeling and experimental investigation of infiltration of sodium chloride solution into nonviable liver tissue.

UNLABELLED: The aim of this study was to establish a mathematical model of the infiltration of sodium chloride solution into cadaveric liver tissue. METHODS: The time law of the flow of the infiltrated fluid at every node of the finite element model was obtained in terms of Darcy's velocity, pressure, and volumetric saturation fraction. The model equations interpret the liver tissue as a porous medium taking into account the hydraulic conductivity, capacity, and absorption mechanisms. Capability of the cadaveric liver tissue to absorb the fluid is taken into account by means of the nonlinear relationship of hydraulic capacity and absorption coefficients against the volumetric saturation fraction. To explain certain inadequacies between the computational model and experiment, the idealized models of empty blood vessels in the vicinity of the injection probe have been used. The model has been implemented in computational environment COMSOL Multiphysics. Experimental procedures were performed to analyze fluid infiltration and to calculate volume of fluid, which might be injected into certain volume of nonviable liver tissue. RESULTS: The necessary physical constants of hydraulic conductivity, capacity, and absorption of liver tissue have been determined by comparing the simulation results against the experimental data. The congruence of the modeling results against the experiment may be regarded as satisfactory. CONCLUSION: The established model analyses distribution of injected solution taking into account the hydraulic conductivity, capacity, and absorption mechanisms of liver tissue. The obtained results are of importance developing complex models of electro-thermal heating coupled with heat advection by means of infiltrated sodium chloride solution.

Investigation of radiofrequency ablation process in liver tissue by finite element modeling and experiment.

BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

Finite element analysis of stresses in the maxillary and mandibular dental arches and TMJ articular discs during clenching into maximum intercuspation, anterior and unilateral posterior occlusion.

The objective of this study was to investigate distribution of stresses in the human TMJ discs, generated during clenching into various occlusal positions. The work presents a biomechanical finite element model of interaction of mandibular and maxillary dental arches and the TMJ discs of a particular person, based on real geometrical data obtained from spiral computed tomography two-dimensional images. 3D contour coordinates - point clouds were collected from these images and solid model was created. The system under investigation consisted of eight basic parts: two rigid structures representing the mandibular and maxillary dental arches, two mandibular condyles, two mandibular fossae of temporal bone, and solid models of two articular discs. The model of maxillary dental arch was fixed in space. The model of the mandibular dental arch was able to move in space synchronically with the mandibular condyles under action of applied forces, which were considered as prescribed and known at insertion points of masticatory muscles. The motion of the mandible was constrained by interdental contact interactions and contact interaction with articular discs, which were situated in between mandibular condyles and mandibular fossae of temporal bone. The model was implemented by using LS-DYNA finite element software. The obtained results presented a 3D view of stresses exhibited in the articular discs, as well as the real contact points of dental interactions at given masticatory geometry of a particular subject and the values of interaction forces. The expected practical value of the developed model is the facilitation of biomechanical evaluations of the influence of tolerances of teeth shapes and occlusal areas together with the supporting areas on the final stress distribution in the dental arches and articular discs.

A revised approach of human mastication function rehabilitation through monotypical mastication analysis.

OBJECTIVE: The aim of the simulation was to find the forcing laws, which provide the close-to reality mastication motions of the components of the system and to investigate the contact zones, interaction forces and their action points as they vary in time. The loss of one or few elements of the mastication system can be restored without significant violations of the overall function provided the general correlations among the mastication system elements, which were influenced during the evolutionary development, have been determined in advance. MATERIALS AND METHODS: We present an approach based on the computer simulation of mastication biomechanics on the basis of finite element (FE) models. They were generated by using the data acquired with both optical and CT scanning systems, which enabled to obtain highly accurate three-dimensional geometrical models of all hard parts of the mastication system of a real dead goat. The surfaces of dental arcs of upper and lower jaws mechanically interacting one against another have been used as the main parts of the model. RESULTS: Using FE models we discovered that mastication forces are correlated directly between dental arches and TMJ surfaces. Factors influencing geometry of dental arches results a destroy jaw function. CONCLUSION: In the course of this analysis the mastication system of a goat has been considered as a representative of the ruminant individual and enabled to demonstrate the mechanics of the mastication process with insights for evaluation of the similarities and differences against the human mastication.