| Liver cancer is a malignant cancer of high morbidity and fatality rate. In recent years, thermal ablation has been widely used in treatment of liver tumors because of its low cost, satisfying efficacy and minimal invasiveness. Treatment planning specific to the liver tumor is a key issue in thermal ablation.This thesis aims at developing a planning system of thermal ablation for liver tumors and improving the accuracy of temperature simulation. The SAR(Specific Absorption Rate) distribution in microwave ablation(MWA) was calculated based on experimental data, and three conditions were proposed to increase the accuracy of SAR calculation. We also proposed a new voltage calibration method in simulation of temperature-controlled radiofrequency ablation(RFA), and investigated the feasibility of Hyperbolic Bioheat Equation(HBE) in RFA simulation with longer durations and higher power. Finally, a planning system of thermal ablation for liver tumors was developed to assist clinicians in determining optimized thermal dosage. The main research contents of this thesis are as follows.1. Calculation of three-dimensional SAR distribution for water-cooled MWA. A total of 75 experiments were conducted. We verified the simulation results by experimental temperature measurements on 22 specific points. First, we quantitatively calculated the influence of temperature error by adding zero mean Gaussian noise to the experimental data. Second, the most effective experimental time points were studied and selected for SAR fitting. Finally, we improved the fitting accuracy by putting forward a weighted least-squares fitting method for SAR calculation.By conducting calculation and comparing the simulation results, we found that the simulation results were normal when the experimental temperature error was less than 3.5? and when we selected the time of 0-60 s?0-70 s,…, 0-110 s to fit the SAR equation. We also found the weighted least-squares fitting method was more stable and effective than the traditional method.2. Study on the key technology of temperature simulation for temperature-controlled RFA. A total of 40 RFA experiments were conducted in liver-mimicking phantom. Four mathematical models with multi-polar electrode were developed by Finite Element Method(FEM) in COMSOL software: HBE with/without temperature-varied voltage calibration, and Pennes bioheat equation(PBE) with/without voltage temperature-varied calibration. The temperature-varied voltage calibration used in simulation was calculated from experimental power output. We verified the effectiveness of different bio-heat equations and different voltage setting methods in simulations by experimental temperature measurements on nine points of the tissue phantom.The result of comparison between experiments and simulations showed that the proposed temperature-varied voltage calibration could improve the accuracy of temperature field simulation for temperature-controlled RFA. Besides, for temperature-controlled RFA simulation with the temperature-varied voltage calibration, the HBE method was 0.55? more accurate than the PBE method.3. Development of a planning system of thermal ablation for liver tumors. Using the Microsoft Visual C++ software, we built the three-dimensional visualization model of tumors, and constructed the finite element simulation model of the temperature field to obtain the best thermal treatment planning scheme.The main idea of this thesis is to focus on the temperature simulations of water-cooled MWA and temperature-controlled RFA. A planning system of thermal ablation has been developed based on the high accuracy and efficiency temperature simulation to assist clinicians in treatment planning. |
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