| Magnetic resonance imaging (MRI) is a diagnostic imaging modality that offers exceptional anatomical detail in standard applications such as studies in the central nervous system. More recently, it has been instrumental in the development of image-guided thermal ablation as a practical "surgical" alternative to tumor resection, owing to its multi-capability in image guidance, temperature monitoring, and assessment. However, more effective methods to control and monitor heating effects, and more accurate means to assess damage post-ablation, must be firmly established before its widespread adoption in the clinic becomes a reality.; This thesis addresses the problems of (1) good control of heat delivery and (2) accurate assessment of tissue damage post-ablation. In the first part of the thesis, determination of tissue thermal properties at the site of interest is proposed for more accurate control of the power required to achieve a desired temperature. A non-invasive method based on MRI-monitoring of thermal decay following a short focused ultrasound (FUS) pulse is described for the separate determination of thermal conductivity and perfusion. In the second part of the thesis, a new application of contrast kinetics is considered for improved assessment through the discrimination of subtle FUS-induced tissue changes. The method was evaluated in rabbits in a series of acute, sub-acute, and chronic studies. The feasibility of more accurate determination of the boundary of necrosis and better differentiation of tissue changes not visible on conventional MRI, was demonstrated.; These results have provided solutions to a few key practicality issues of image-guided thermal ablation. Further development of the concepts and methods proposed in this thesis hopefully will facilitate the widespread adoption of thermal ablation in the clinical setting. |
