Late Gadolinium-Enhancement Cardiac Magnetic Resonance Identifies Postinfarction Myocardial Fibrosis and the Border Zone at the Near Cellular Level in Ex Vivo Rat Heart

Abstract

Background— Using a resolution 1000-fold higher than prior studies, we studied (1) the degree to which late gadolinium-enhancement (LGE) cardiac magnetic resonance tracks fibrosis from chronic myocardial infarction and (2) the relationship between intermediate signal intensity and partial volume averaging at distinct “smooth” infarct borders versus disorganized mixtures of fibrosis and viable cardiomyocytes. Methods and Results— Sprague-Dawley rats underwent myocardial infarction by coronary ligation. Two months later, rats were euthanized 10 minutes after administration of 0.3 mmol/kg intravenous gadolinium. LGE images ex vivo at 7 T with a 3D gradient echo sequence with 50×50×50 μm voxels were compared with histological sections (Masson trichrome). Planimetered histological and LGE regions of fibrosis correlated well ( y =1.01 x −0.01; R 2 =0.96; P <0.001). In addition, LGE images routinely detected clefts of viable cardiomyocytes 2 to 4 cells thick that separated bands of fibrous tissue. Although LGE clearly detected disorganized mixtures of fibrosis and viable cardiomyocytes characterized by intermediate signal intensity voxels, the percentage of apparent intermediate signal intensity myocardium increased significantly ( P <0.01) when image resolution was degraded to resemble clinical resolution consistent with significant partial volume averaging. Conclusions— These data provide important validation of LGE at nearly the cellular level for detection of fibrosis after myocardial infarction. Although LGE can detect heterogeneous patches of fibrosis and viable cardiomyocytes as patches of intermediate signal intensity, the percentage of intermediate signal intensity voxels is resolution dependent. Thus, at clinical resolutions, distinguishing the peri-infarct border zone from partial volume averaging with LGE is challenging.

Speckle Tracking Echocardiography Detects Uremic Cardiomyopathy Early and Predicts Cardiovascular Mortality in ESRD

“…49 Late gadolinium enhancement imaging via cardiac magnetic resonance imaging is the gold standard method for the noninvasive evaluation of cardiac fibrosis. 50 Fibrosis severity detected via late gadolinium enhancement correlates significantly with STE-assessed strain parameters in patients with hypertrophic cardiomyopathy and Fabry disease. 19,20,23 However, in patients with higher-stage CKD and those with ESRD, gadolinium is contraindicated because of the risk of nephrogenic systemic fibrosis.…”

Infarct Characterization and Quantification by Delayed Enhancement Cardiac Magnetic Resonance Imaging Is a Powerful Independent and Incremental Predictor of Mortality in Patients With Advanced Ischemic Cardiomyopathy

“…Schelbert et al 17 recently demonstrated the ability of highfield DHE-CMR to identify areas of fibrous tissue interspersed with viable myocardial cells in the periphery of infarct with image resolution of 50×51×51 μm. However, this study demonstrated that as image resolution decreased, more partial volume averaging occurred, resulting in overestimation of the PI area.…”

Role of Imaging in Ablation Therapy of Ventricular Arrhythmias

“…In ex-vivo MRI, spatial resolution is close to the myocyte level, with a spatial resolution of 50×50×50 µm. 6 Often, only focal delayed enhancement can be identified, and detection of diffuse fibrosis is currently still limited. Be- cause often the fibrotic process is not as extensive as post-infarction scarring, but instead limited to increased collagenous tissue deposited around individual viable cells, the signal intensity is closer to that of normal tissue.…”

“…Schelbert et al in their high-resolution ex-vivo animal study showed that areas of intermediate signal intensity corresponded to surviving muscle bundles within scar. 6 However, when they used retrospective degradation of the MR images to obtain a lower resolution comparable to that of clinical scans, areas of intermediate signal intensity were often due to volume averaging. Further animal experiments where postinfarction VTs were mapped demonstrated that with highresolution MRI, viable myofibers could be detected within the isthmus area of a post-infarction scar.…”