FINITE ELEMENT MODELING OF HEPATIC RADIO FREQUENCY ABLATION by

Radio-Frequency (RF) ablation is a minimally invasive method for treatment of primary and metastatic hepatic tumors. A catheter is introduced transcutaneously into the tumor, and tissue is heated up by application of radio-frequency current. In this work, I present the application of the Finite Element Method (FEM) for creating models of hepatic RF ablation to evaluate and improve catheter design. In Chapter II I present an automated method for FEM modeling temperaturecontrolled RF ablation. In Chapter III I present a novel bipolar method, where current travels between two multiprong electrodes instead of between a single electrode and a dispersive electrode. I present FEM models, and in-vivo results for the bipolar method. Bipolar RF ablation creates about three times larger lesions compared to conventional RF ablation. In Chapter IV I present FEM analysis of three different methods that allow multiple usage of RF catheters simultaneously. Currently, commercial available generators only allow use of a single RF probe at a time. Use of multiple probes reduces treatment time and allows treatment of large tumors, or multiple metastases simultaneously. iv In Chapter V I present a prototype developed from a commercial RF system, which allows use of two RF probes at a time. RF power is rapidly switched between two probes. Effectively, both probes heat up simultaneously, and by varying the time interval for which power is applied to each probe, both probes can be kept at same temperature. I present exvivo results that prove feasibility of this method. In Chapter VI I present FEM models of the bipolar method, using 10-prong probes next to a blood vessel. Local tumor recurrence is associated with tumor cell survival next to blood vessel. Bipolar RF ablation allows creation of lesions closer to blood vessels, compared to conventional RF ablation. This may reduce local recurrence rates. In Chapter VII I present FEM models of a cool-tip probe next to a blood vessel. In Chapter VIII I evaluate four different methods that allow assessment of where heat is dissipated. In Chapter IX I show FEM models of ablation, carried out at audio frequencies. Tumor exhibits significantly different conductivity compared to normal liver tissue, most notably at lower frequencies. I evaluate if ablation at lower frequencies improves performance. Ablation at low frequencies preferentially targets tumor tissue, and preserves normal liver tissue. Higher temperatures are reached within cancer tissue than in liver tissue, compared to conventional RF ablation. This may help reduce local recurrence rates.