MRI-guided radiofrequency thermal ablation: 3D correlation of MR lesion images with tissue viability for immediate post-ablation treatment assessment

Solid tumors can be treated using radiofrequency (RF) thermal ablation under interventional magnetic resonance (MR) image guidance. We are investigating the ability of MR to accurately predict the region of cell death by comparing MR thermal lesion images to tissue damage as seen histologically. We developed a methodology using a three-dimensional computer registration for making spatial correlations. An open MR imaging system was used to guide an ablation electrode into rabbit thigh muscles and acquire in vivo post-ablation MR volumes. After MR and histology images were aligned with a registration accuracy of 1.32±0.39 mm (mean±SD), we compared a boundary of necrosis identified in histology with the outer boundary of the hyperintense rim in gadolinium contrast-enhanced (CE) Tl-weighted MR images. For 14 histology images from five lesions, the mean absolute distance between boundaries was 0.94±0.44 mm. Since the small discrepancy is comparable to our ability to measure such errors, these boundaries may match exactly. Similar correlations to histology were obtained from experiments with rabbits sacrificed four days post-ablation. This is good evidence that during RF ablation treatments, MR images can accurately localize the zone of necrosis at the lesion margin.