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

Abstract

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 +/- 8.4) with a surrounding 0.5-mm low-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 intralesional pathology during 12-hour follow-up. This finding confirms a possible role of MRI in guiding and evaluating RF application during electrophysiologic ablation procedures.

Figure 1

Time-course of RF lesions. Shown are 30W, 40W and 50W epicardial ablation lesions after 30min, 1h, 3h, 6h, and 12h of follow-up using T2-weighted MR imaging and the corresponding pathological specimen (EP-epicardium, EN-endocardium, RV-right ventricular wall).

Figure 2

Time-course of RF lesions. Shown are 30W, 40W and 50W epicardial ablation lesions at 30min, 1h, 3h, 6h, and 12h of follow-up using T1-weighted MR imaging and the corresponding pathological specimen (EP-epicardium, EN-endocardium, RV-right ventricular wall).

Figure 3

Correlation of RF lesion size. Comparison of the ablation size in the pathological specimen and the corresponding MRI using T2-weighted and T1- weighted imaging protocols.

Figure 4

Influence of time and applied RF energy on Contrast-to-Noise Ratio (CNR) of RF Lesions. Twelve hours of follow-up of CNR on RF lesions created with an increasing amount of RF energy using T2-weighted (fast spin-echo or FSE) and T1-weighted (spoiled gradient recall acquisition or SPGR) MR imaging protocols.

Figure 5

Size of RF ablations during 12h follow-up. Lesion size of individual RF energy group over 12h follow-up as determined by T2-weighted and T1-weighted MR images.

Figure 6

Heterogeneity of RF lesion. Increasing heterogeneity of RF ablations (measured as the standard deviation of the signal intensities over the lesion area) with increasing amount of applied RF energy assessed with T2-weighted and T1-weighted MR images.

Figure 7

Intralesional Pathology. Necrotic cavities within high-energy RF ablation lesions and corresponding pathological specimen. Typical appearance of intralesional necrotic cavities as (a) areas of increased signal intensity in T2-weighted MRI, and (b) areas of decreased signal intensities in T1-weighted MR images, (c) corresponding gross pathology, and (d) histology (Masson’s Trichrome stain).