Abstract 17144: Assessment of Tissue Heating During Cardiac Radiofrequency Ablation Using Referenceless MRI Thermography
Introduction: Imaging tissue heating during RF ablation may permit more accurate placement and titration of ablation lesions. Standard proton resonance frequency shift MRI thermography, however, is limited by sensitivity to physiologic motion and scanner phase drift between acquisition of ablation and reference pre-heating images. The aim of this study is to assess the feasibility of referenceless MRI thermography which addresses this limitation by eliminating need for a separate pre-heating image but has not yet been applied to cardiac ablation.
Methods: An MRI compatible copper electrode catheter was inserted into the left ventricle in 6 dogs. Gradient recalled echo images were acquired while applying RF power in 3W increments until high impedance was reached. Gross pathology was obtained. The pre-heating image was estimated from the ablation image phase component (A) by unwrapping phase (B), masking the catheter tip region where heating was expected (C), and extrapolating phase from unmasked regions of the heart using a fourth order polynomial fit (D). Thermography images were then computed using standard methods (E). Thermography lesion extent was defined by tissue temperature above 50°C. Electrode artifact was defined by darkened myocardium adjacent to the catheter tip on the magnitude component of the ablation image.
Results: Transmural lesion extent by referenceless MR thermography was within 20% of that obtained by pathology (inset F) in the four cases where the electrode artifact transmurality was less than 25%. However, thermography and pathology lesion extent differed by over 60% in the two cases where electrode artifact transmurality was greater than 40%.
Conclusion: Referenceless MR thermography of cardiac RF ablation is possible and may permit more practical MR thermography monitoring of cardiac ablation. Reducing electrode artifact by using lower magnetic susceptibility materials appears required for more reliable temperature assessment.
- © 2011 by American Heart Association, Inc.