Computers in Biology and Medicine 38 (2008) 694 – 708 www.intl.elsevierhealth.com/journals/cobm Finite element modeling of cooled-tip probe radiofrequency ablation processes in liver tissue  Rimantas Barauskas a , Antanas Gulbinas b , Tomas Vanagas c , Giedrius Barauskas c , ∗ a Department of System Analysis, Kaunas University of Technology, Kaunas, Lithuania b Institute for Biomedical Research, Kaunas University of Medicine, Kaunas, Lithuania c Department of Surgery, Kaunas University of Medicine, Eiveniu str. 2, LT-50009 Kaunas, Lithuania Received 13 November 2006; accepted 18 March 2008 Abstract 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.  2008 Elsevier Ltd. All rights reserved. Keywords: Radiofrequency ablation; Computational modeling; Hydraulic conductivity; Experimental research 1. Introduction The substantial proportion of patients with primary or metastatic malignancies confined to the liver are not candidates for resection because of tumor size, location, multifocal char- acter or inadequate functional hepatic reserve [1]. Radiofre- quency ablation (RFA), a local thermal ablative technique for the treatment of unresectable hepatic tumors including hepatocellular carcinoma, proved to be tumoricidal [2]. RFA takes place at frequencies 460–550 kHz. Electrical volt- age is being applied to the ablation zone by means of an elec- trically active probe. The flow of electrical current transfers the energy to the tissue, and the temperature there reaches 100 ◦ C during time interval of 10–15 min [3,4]. The basic physical pro- cesses taking place during RFA are the electrical current flow- ing in the tissue and causing volumetric heat generation, as well as, the heat exchange due to thermal conductance of tissues.  The study was sponsored by the Lithuanian Science and Studies Foun- dation. ∗ Corresponding author. Tel.: +370 686 525 96; fax: +370 37 326 824. E-mail addresses: rimantas.barauskas@ktu.lt (R. Barauskas), gulbanta@gmail.com (A. Gulbinas), giedrius.barauskas@gmail.com (G. Barauskas). 0010-4825/$ - see front matter  2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.compbiomed.2008.03.007 The electrical conductivity is dependent on the temperature of the tissue, therefore a coupled electro-thermal problem can be formulated [6]. RFA processes performed by using cooled-tip ablation probes are physically more complex because of the flow of sodium chloride (NaCl) solution injected through the active part of the ablation probe in order to prevent tissue car- bonization, which may impede or even block the heat transfer into the tissue. The infiltration flow of the injected solution makes a signif- icant influence on the overall heat transfer process of RFA due to marked amount of heat energy transferred into the tissue by advection, which is the transport of heat by means of moving fluid. The heat power transferred by the fluid flow at each point of the tissue depends on the velocity of the fluid, therefore it has to be calculated by solving the hydraulic conductiv- ity partial differential equations and further employed in the advection–diffusion equation, which describes the combined process of heat transfer. As a final result, the advection makes the heated zone wider spread and simultaneously the peak tem- perature in the nearest vicinity of the electrode is lower than in the case of purely conductive heat exchange. The heating of the tissue by high frequency electrical current together with the heat conductivity and advection mechanisms complete the