Three dimensional correlation of MR images to muscle tissue response for interventional MRI thermal ablation

Solid tumors and other pathologies are being treated using radio-frequency (RF) ablation under interventional magnetic resonance imaging (iMRI) guidance. In animal experiments, we are investigating the ability of MR to monitor ablation treatments by comparing MR images of thermal lesions to histologically assayed cellular damage. We developed a new methodology using three-dimensional registration for making spatial correlations. A low-field, open MRI system was used to guide an ablation probe into the thigh muscle of 5 rabbits and acquire MR volumes post ablation. After the in vivo MR and histology images were aligned with a registration accuracy of 1.32 +/- 0.39 mm (mean +/- SD), a boundary of necrosis identified in histology images was compared with manually segmented boundaries of the elliptical hyperintense region in MR images. For 14 MR images, we determined that the outer boundary of the hyperintense region in MR, closely corresponds to the region of cell death, with an absolute distance between boundaries of 0.96 +/- 0.34 mm (mean +/- SD). Since this distance may be less than our ability to measure such differences, boundaries may match perfectly. This is good evidence that MR lesion images can localize the region of cell death during RF ablation treatments.