Perfusion-modulated MR imaging-guided radiofrequency ablation of the kidney in a porcine model

Objective.This study was performed to test the hypothesis that temporary re nal ischemia will result in increased thermal lesion size during radiofrequ ency thermal ablation in the kidney. Materials and methods. Twelve kidneys were treated in six pigs that were pl aced under general anesthesia in the MR suite, using a 0.2-T open C-shaped MR imaging system. A 4-cm-long, 14-mm-diameter balloon catheter was placed into the aorta using a transfemoral approach, and the balloon was positione d proximal to the renal arteries via guidance with MR imaging. A 2-cm expos ed-tip MR-compatible 17-gauge radiofrequency electrode was placed into one kidney under MR fluoroscopy using fast imaging with steady-state free prece ssion (FISP) sequences. Thermal ablation was performed with the electrode t ip temperature maintained at 90 +/- 2 degreesC for 10 min. This procedure w as repeated in the contralateral kidney. The balloon was inflated during on e ablation. Postablation images were obtained, the pigs were sacrificed, an d both kidneys of each animal were harvested for pathologic correlation. Results. Technical success was achieved in all animals. The lesion measured 14.2 +/- 2.2 mm (mean +/- standard deviation) for the ischemic kidney vers us 8.0 +/- 2.6 mm in the normally perfused kidney (p = 0.00002). No signifi cant complications were noted. In all images, thermal lesions displayed low signal intensity with a sharp rim of high signal intensity best visualized using short tau inversion recovery (STIR) sequences with a mean accuracy o f 1.3 +/- 1.2 mm when compared with pathologic findings and a mean contrast -to-noise ratio of 4.9 +/- 2.5. Conclusion. We accept the hypothesis that temporary renal ischemia leads to a significantly increased radiofrequency ablation lesion size. We conclude that catheter-based balloon perfusion reduction is feasible, that the proc edure does nor lead to major complications, and that it can be performed us ing MR imaging as the sole imaging modality.