Abstract 14877: Native T1-based Cardiovascular Magnetic Resonance for Characterizing Chronic Myocardial Infarctions: Proof-of-Concept Study in Canines

Abstract

Introduction: Gadolinium infusion required for Late Gadolinium Enhancement (LGE) Cardiovascular Magnetic Resonance (CMR) imaging is contraindicated in nearly 20% of myocardial infarction (MI) patients due to chronic end-stage kidney disease. Hypothesis: Using a canine model of MI, we investigated whether native T1 mapping at 3T could be an alternative to LGE CMR for characterizing chronic MIs (CMIs). Methods: Canines (n=29) were subjected to ischemia-reperfusion injury. Native T1 maps, native T2 maps and LGE images were acquired at 7 days (acute, AMI) and 4 months (CMI) post-MI at 1.5T and 3T. Infarct location, size and transmurality, measured using Mean + 5 Standard Deviations criterion, were compared between T1 maps and LGE images. Native T2 maps were used to examine the resolution of edema between AMI and CMI. Following the CMR studies, animals were euthanized and ex-vivo histology was performed. Results: T1 maps and LGE images were not different for measuring infarct size (p=0.61) and transmurality (p=0.81) in CMI at 3T. In AMI at 3T, T1 maps overestimated both infarct size (p=0.007) and transmurality (p=0.007) relative to LGE images. At 1.5T, T1 maps underestimated both infarct size and transmurality relative to LGE images in both AMI and CMI (p<0.001 for all cases). Relative to the remote territories, T1 of the infarcted myocardium was elevated in AMI (3T: p<0.001; 1.5T: p<0.001) and CMI (3T: p<0.001; 1.5T: p=0.037). T2 of the infarcted myocardium was elevated in AMI (p<0.001 at both 3T and 1.5T), but not in CMI (3T: p=0.19, 1.5T: p=0.55) indicating that myocardial edema resolved by 4 months post-MI. Masson’s trichrome staining showed extensive replacement fibrosis within CMIs. Sensitivity and specificity of T1 maps to detect CMI were 95% and 97% respectively at 3T, and 58% and 78% respectively at 1.5T. Conclusions: Native T1 mapping at 3T can characterize CMIs with high diagnostic accuracy. T1 elongations in CMI appear to arise predominantly from replacement fibrosis.