Investigation of thermal field in energy-based biomedical applications

Energy-based biomedical applications have achieved wide success in the past fifty years by using new technologies, such as RF, microwave, laser, and ultrasound. However, the full potential of energy-based treatment in clinical applications has not been realized due to the lack of almost real-time and accurate prediction of temperature. To meet this need, in vivo knowledge of the tissue properties feeding into an experimentally verified numerical model simulating the underlying physical phenomena in the treatment is required. In this thesis, an integrated numerical and experimental study was carried out to develop more advanced tools aimed at solving several specific problems in two typical energy based biomedical applications, hyperthermia and RF ablation.; First, an integrated numerical simulation procedure, which includes the electromagnetic and thermal simulation, was developed to accurately predict the temperature distribution of a canine tumor undergoing hyperthermia treatment. The numerical parametric study showed that the geometric shape of the tumor has a more significant effect on the temperature field compared with perfusion and other parameters. This numerical tool was used to design a novel double spiral applicator with the advantage of flexible energy delivery and the applicator performance was experimentally validated. In order to significantly reduce the computation time for temperature prediction, our in-house developed artificial neural network software was deployed to simulate the temperature field during hyperthermia treatment and its prediction accuracy was validated.; After the numerical tools were successfully developed, micro sensors were developed for tissue characterization. First, a micromachined electrical probe was developed for real-time local measurement of electrical conductivity of tissues. The probe was also used to investigate the electrical conductivity change induced by temperature elevation. The results showed that the electrical conductivity doubles from room temperature to 90°C. Following this, a novel thermal conductivity probe for local measurement of thermal properties of tissue was fabricated by micromachining. The theoretical and numerical analysis demonstrated that the calculated thermal conductivity is simply the average of the thermal conductivity of the tissue and the substrate. The probe was used to investigate the change of thermal conductivity of pig liver before and after RF ablation treatment and the relationship between effective thermal conductivity and RF ablation area. The results showed that pig liver after ablation has a slightly higher thermal conductivity than before, and the outcome area of RF ablation can be predicted from the measurement values of effective thermal conductivity.