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- Open Access
Intrinsic MRI visualizes RF lesions within minutes after MR-guided ablation
https://doi.org/10.1186/1532-429X-18-S1-P206
© Krahn et al. 2016
- Published: 27 January 2016
Keywords
- Structural Heart Disease
- Ablation Lesion
- Lesion Core
- Edematous Area
- Myocardial Hyperenhancement
Background
MR visualization of RF lesions is an application of growing interest with the potential for translation to clinical ablation procedures. In particular, intrinsic-contrast MRI avoids the dynamic contrast produced in typical Gd-based MRI, and may differentiate the reversible and irreversible thermal injury thought to be caused by RF ablation. This distinction is important for assessing the permanence of ablation to eradicate the substrate of ventricular tachycardia in structural heart disease. In this study we investigate the potential of intrinsic-contrast MRI to visualize the features of thermal injury and evolution of RF lesions that may occur immediately after ablation.
Methods
8 RF ablation lesions were created in vivo in 4 healthy pigs. Active real-time MR tracking [1] guided navigation of an MR-enabled catheter (Imricor Medical Systems) within the LV. During ablation, 30-40W was applied to the LV endocardium for 45-60s with catheter tip irrigation throughout. MR images were acquired repeatedly during the ensuing 1-2h, a time frame relevant to the length of clinical ablation procedures. The imaging protocol consisted primarily of T2-prepared b-SSFP for T2 mapping and IR-prepared b-SSFP. In T2 maps, long-T2 regions representative of inflamed, edematous tissue were delineated semi-automatically using a threshold of T2=55ms, approximately 3SD above remote as per established methods describing edema in T2-weighted images [2]. Further, we manually delineated the core of RF lesions based on myocardial hyperenhancement in IR-SSFP images as in [3]. In all analysis, one-tailed t-test was used and p < 0.05 considered significant.
Results
(a) T 2 maps depicting an RF lesion at 4 time points after ablation. Images were acquired using a 4-channel cardiac anterior array at 4 echo times: TE=3, 24, 88, & 184 ms and fitted using a 3-parameter model (resolution = 0.9 × 0.9 × 6 mm). (b) Area of edema with time after ablation for the same lesion. The edematous region grew in size by 110%, and this positive trend was significant with p < 0.05 for the fitted line.
(a) IR-SSFP images depicting an RF lesion (same lesion as shown in Figure 1) at 3 time points after ablation. Images were acquired using the following parameters: TE/TR=2/6 ms, resolution = 0.9 × 0.9 × 6 mm, and TI=730-775 ms (within the range of TI yielding optimal contrast [3]). (b) Area of the necrotic core with time after ablation for the same lesion. The slope of the fitted line was not significantly different from 0.
Conclusions
We successfully demonstrated the visualization of RF lesions using intrinsic-contrast MRI during a time frame spanning minutes to hours after ablation. The presence of edema is of particular interest as it is thought to temporarily alter myocardial excitability, confounding clinical tests used to confirm RF ablation procedural success. This valuable description of RF lesions could be integral in future ablation procedures performed concurrently with MRI feedback.
Authors’ Affiliations
Copyright
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
