Characterization of acute and subacute radiofrequency ablation lesions with nonenhanced magnetic resonance imaging

BACKGROUND Magnetic resonance imaging (MRI) has the potential to visualize radiofrequency (RF) ablations, which have become the preferred strategy for treatment of many arrhythmias. However, MRI patterns after RF ablation have not been well investigated. OBJECTIVE The purpose of this study was to define the characteristic appearance and the effect of time and energy on noncontrast-enhanced MRI of RF ablation. METHODS Using a power-controlled, cooled-tip ablation system, RF ablation Lesions (5-50 W for 45 seconds) were created on the right ventricular epicardium in 10 mongrel dogs. T1- and T2-weighted MR images were obtained during 12-hour follow-up and compared with gross anatomy and histopathology. RESULTS Lesions were successfully visualized with T2- and T1-weighted images 30 minutes to 12 hours after RF ablation. T2 images were more consistent and displayed a characteristic elliptical, high-signal core (contrast-to-noise-ratio [CNR] = 18.9 +/- 18.4) with a surrounding 0.5-mm tow-intensity rim that on histopathology corresponded to the central tissue necrosis and the transition zone, respectively. T1 images showed a less remarked increase in signal intensity (CNR = 9.6 +/- 7.4) without a surrounding rim. Lesion size and appearance were well defined and unchanged during the 12-hour follow-up (analysis of variance). CNR was independent of applied RF energy and allowed accurate assessment of RF ablation at all time points (r = 0.87 and r = 0.83 for T2 and T1 images, respectively). Transmural Lesions, interlesional gaps, and intralesional pathology could be reliably predicted in >90%. CONCLUSION Noncontrast-enhanced MRI allows accurate assessment of RF ablation and its intratesional pathology during 12-hour follow-up. This finding confirms a possible rote of MRI in guiding and evaluating RF application during electrophysiologic ablation procedures.