MR imaging-guided radio-frequency thermal ablation of the lumbar vertebrae in porcine models

PURPOSE: To test the hypotheses that (a) magnetic resonance (MR) imaging-guided radio-frequency (RF) thermal ablation of the vertebrae is feasible in porcine models, (b) procedure safety depends on the location of ablation within the vertebra, and (c) MR imaging allows accurate monitoring of induced thermal lesion size and shape. MATERIALS AND METHODS: Ten percutaneous MR imaging-guided RF thermal ablations were randomized over various lumbar vertebral levels and locations in seven pigs. Animals were followed up for 2, 7, or 14 days before sacrifice. Thermal lesion size and shape as measured on MR images obtained immediately after ablation and at follow-up were compared with gross pathologic findings. Mean absolute differences between lesion diameters at pathologic examination and MR imaging were evaluated by using a paired t test, as were differences between lesion-to-vertebra contrast-to-noise ratios obtained for each sequence. Clinical and imaging data were correlated with histologic findings. RESULTS: Successful RF electrode placement in the targeted part of the vertebra was achieved in all procedures, Ablations performed away from neural elements were safe to perform. Pedicular ablations resulted in radiculopathy, whereas ablations performed directly over the posterior cortex resulted in paraplegia. Lesion sizes measured on T2-weighted images were closest to those measured at gross pathologic examination (mean absolute difference, 0.72 m ± 0.83 [SD]), followed by those measured on contrast material-enhanced T1-weighted (1.27 mm ± 0.83) and short inversion time inversion-recovery (STIR) (1.5 mm ± 1.84) images. Size measurements obtained on T2-weighted images were significantly closer to gross pathologic measurements than were those obtained on contrast-enhanced T1-weighted images (P = .013) but were not different from those obtained on STIR (P = .27) images. The contrast-to-noise ratio was significantly higher for contrast-enhanced T1-weighted images than for T2-weighted (P < .001) or STIR (P < .001) images. CONCLUSION: MR imaging-guided RF thermal ablation of the vertebrae is feasible in porcine models, but the safety of the procedure depends on the location of ablation within the vertebra. MR imaging allows accurate monitoring of thermal lesion size and shape.