Volume 18 Supplement 1

19th Annual SCMR Scientific Sessions

Open Access

T2*-weighted MRI technique for visualization of RF ablation lesions

  • Eugene Kholmovski1, 2,
  • Ravi Ranjan2,
  • Nathan Angel2 and
  • Nassir F Marrouche2
Journal of Cardiovascular Magnetic Resonance201618(Suppl 1):O128

https://doi.org/10.1186/1532-429X-18-S1-O128

Published: 27 January 2016

Background

LGE-MRI is widely used to assess cardiac RF ablation lesions. However, LGE-MRI requires contrast injection and the appearance, dimensions and visibility of lesions in LGE-MRI noticeably change with time after ablation and time after contrast injection. Recently proposed non-contrast T1-weighted (T1w) technique is only applicable to visualize acute (< 3 days) RF lesions. The main goal of this study was to develop and validate a non-contrast MRI technique for assessment of sub-acute (> 3 days) RF ablations.

Methods

Non-contrast T2*-weighted (T2*w) MRI technique for RF lesion visualization has been implemented. This technique exploits the difference in T2* relaxation between normal and ablated myocardium. Reduction in T2* relaxation time of ablated myocardial tissues is caused by the transformation of hemoglobin into hemosiderin from ruptured and obstructed blood vessels as a result of RF ablation. To validate this technique, RF ablations were performed in 6 canines using ThermoCool catheter (Biosense Webster) at 30 Watts for 30 seconds. Imaging studies were performed on a 3T scanner (Verio, Siemens HealthCare) at 0, 1, 4, and 8 weeks post-ablation. Study protocol included T1w, T2*w, and LGE scans with a resolution of 1.25 × 1.25 × 2.5 mm and T1, T2 and T2* mapping.

Results

Dependence of T2* relaxation time of ablated and normal myocardium on time after ablation is shown in Fig. 1. T2* of normal myocardium was similar for all post-ablation studies (p = N.S.). For acute (0 week) studies, T2* relaxation time of ablated regions (42.0 ± 8.8 ms) was significantly higher (p < 0.001) than T2* for normal myocardium (27.4 ± 3.7 ms). This observation may be explained by the presence of severe edema at the ablated regions. T2* time of RF ablations significantly reduced with time after ablation (p < 0.05) and it was significantly lower than T2* of normal myocardium at 1, 4, and 8 weeks after ablation (p < 0.001).
Figure 1

T2* relaxation time of ablated and normal myocardium vs. time after ablation. Blue bars - normal myocardium, red bars - RF ablation lesions.

Representative T1w, T2*w, and LGE images are shown in Fig. 2, top panel. All RF lesions (n = 28) were detectable on non-contrast T1w images acquired acutely. Lesion visibility in non-contrast T1w MRI was considerably reduced 1 week post-ablation. Visibility of lesions in T2*w images improves with time after ablation. Lesions have hypointense boundaries in T2*w images acquired 1 and 4 weeks post-ablation. Whole lesions are hypointense in T2*w images acquired 8 weeks post-ablation.
Figure 2

Top Panel - Representative images of RF ablation lesion. (a-b) non-contrast T1w acquired (a) acutely and (b) 1 week post-ablation; (c-e) non-contrast T2*w acquired (c) 1, (d) 4, and (e) 8 weeks post-ablation; (f) LGE acquired 8 weeks post-ablation. Bottom Panel - Volume of RF ablation lesions from LGE-MRI vs. volume of the lesions from T2*w. LGE and T2*w were acquired 8 weeks post-ablation.

Strong correlation (R2 = 0.908) between lesions volumes estimated from LGE and T2*w images acquired 8 weeks post-ablation was found (Fig. 2, bottom panel). Lesion volume from T2*w scans was about 27% smaller than lesion volume from LGE scans.

Conclusions

T2* relaxation time of cardiac RF ablation lesions significantly reduces with time after ablation. Non-contrast T2*w technique can be used to visualize sub-acute RF ablations as early as a week post-ablation. Visibility of the lesions in T2*w image considerably improves with time after ablation as T2* relaxation time of the lesions becomes shorter.

Authors’ Affiliations

(1)
UCAIR, Department of Radiology, University of Utah
(2)
CARMA Center, University of Utah

Copyright

© Kholmovski et al. 2016

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.

Advertisement