Three dimensional comparison of interventional MR radiofrequency ablation images with tissue response

Solid tumors are being treated using radio-frequency (RF) ablation under interventional magnetic resonance imaging (MRI) guidance. We are investigating the ability of MR to monitor ablation treatments by comparing MR images of thermal lesions to histologically assayed tissue damage. We developed a methodology using a three dimensional computer registration. An open MRI system was used to guide an electrode into five rabbit thighs and acquire MR volumes post ablation. After MR and histology images were registered with an accuracy of 1.32 ± 0.39 mm (mean ± SD), a boundary of necrosis identified in histology was compared 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 (mean ± SD). Since the small discrepancy between boundaries is comparable to our registration accuracy, the boundaries probably match exactly. Similar correlations to histology were obtained with a deformable model segmentation method. This is good evidence that during treatments, MR images can localize the necrotic region.