Solid tumors are being treated using radiofrequency (RF) thermal ablation under interventional MRI 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. An open MR imaging system was used to guide an RF ablation electrode into rabbit thigh muscles, and acquire in vivo postablation MR volumes. After MR and histology images were registered with an 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 MR images. For 14 T2-weighted MR images, the absolute distance between boundaries was 0.96±0.34 mm. Similar correlations were obtained from experiments with rabbits sacrificed four days postablation. This is good evidence that during ablation treatments, MR images can accurately identify the necrotic region.