Abstract 20497: Late Gadolinium Enhanced MRI Microscopy at Near Cellular Resolution Accurately Delineates Infarct Size in Acute MI and Detects Intermediate Enhancement in Regions with Histologic Evidence of Edema
Introduction: If T2 weighted MRI detects peri-infarct edema around acute myocardial infarction (AMI), then this region should also enhance with gadolinium contrast agents. However, prior studies have lacked the independent histological Methods and near cellular MR resolution needed to detect small areas of late gadolinium enhancement (LGE) in the ischemic but viable border zone.
Hypotheses: 1) AMI size by LGE+MVO (microvascular obstruction) will correlate with regions of myoglobin-negative myocardium. 2) Regions of myocardial edema in the border zone around the infarct will show mild or intermediate enhancement on LGE and evidence of increased extracellular space by Fluorescein Maleimide (FM) labeling - a novel agent that covalently labels the extracellular space.
Method: Twelve Sprague Dawley rats underwent 30 min coronary occlusion and 24 hours of reperfusion: 6 rats to develop histological methods and 6 for LGE correlations. FM and Gd-DTPA were injected in vivo 20 and 10 minutes prior to sacrifice, respectively. LGE images of the heart were acquired ex vivo at 7 Tesla with a 3D gradient echo sequence (voxel = 55×55×55 microns). Infarct size was measured by planimetry on frozen sections stained for myoglobin by immunohistochemistry (IHC) and on corresponding MR images.
Results: Infarct size agreed between LGE and Myoglobin IHC, y=1.04x+0.009, R2 =0.97, p<0.001 (Figure - red planimetered region). FM also outlined the infarct by binding within dead cells. LGE and FM showed patches of intermediate signal intensity in areas deemed viable by myoglobin in 44% of slices (Figure - Arrow).
Conclusion: While MRI showed typical patterns of LGE/MVO for AMI, there were regions of mild-intermediate LGE in viable regions in the border zone (regions stained viable by Myoglobin). FM provided independent histological evidence of increased extracellular space in these regions of mild-intermediate LGE. These regions likely correspond to edema.
- © 2010 by American Heart Association, Inc.