Perfusion-Modulated MR Imaging—Guided Radiofrequency Ablation of the Kidney in a Porcine Model

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Abstract
OBJECTIVE. This study was performed to test the hypothesis that temporary renal ischemia will result in increased thermal lesion size during radiofrequency thermal ablation in the kidney. MATERIALS AND METHODS. Twelve kidneys were treated in six pigs that were placed 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 positioned proximal to the renal arteries via guidance with MR imaging. A 2-cm exposed-tip MR-compatible 17-gauge radiofrequency electrode was placed into one kidney under MR fluoroscopy using fast imaging with steady-state free precession (FISP) sequences. Thermal ablation was performed with the electrode tip temperature maintained at 90 ± 2°C for 10 min. This procedure was repeated in the contralateral kidney. The balloon was inflated during one ablation. Postablation images were obtained, the pigs were sacrificed, and 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 versus 8.0 ± 2.6 mm in the normally perfused kidney (p = 0.00002). No significant 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 of 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 procedure does not lead to major complications, and that it can be performed using MR imaging as the sole imaging modality.