MRI-guided lased thermal ablation: model and parameter estimates relating MR thermometry images to cell death

Solid tumors and other pathologies can be treated using laser thermal ablation under interventional magnetic resonance imaging (iMRI) guidance. We developed a model to predict cell death from MR thermometry measurements and applied it to in vivo rabbit brain data. We aligned post-ablation MR lesion images to gradient echo images, from which temperature is derived, using a mutual information registration method. We used the outer boundary of the hyperintense rim in the post-ablation MR lesion image as the boundary for cell death, as verified from histology. Model parameters were simultaneously estimated using an iterative optimization algorithm applied to every interesting voxel in over 185 images from multiple experiments having various temperature histories. The model gave a voxel sensitivity and specificity of 86.9% and 98.8%, respectively. Mislabeled voxels typically were within one voxel of the segmented necrotic boundary. This is good evidence that iMRI temperature maps can be used with our model to predict therapeutic regions in real-time.