Quantitation of reperfused myocardial infarction by Gd-DOTA-enhanced magnetic resonance imaging. An experimental study.

Because there is evidence that myocardial infarct size is modified by coronary artery reperfusion, an ex vivo experimental model of myocardial infarction was developed to determine the influence of the timing of gadolinium-tetraazacyclododecane tetraacetic acid (Gd-DOTA)-enhanced magnetic resonance imaging (MRI) on the accuracy of infarct size quantitation. Eighteen dogs underwent a 2-hour coronary occlusion followed by 1 (n = 6), 6 (n = 6), or 48 (n = 6) hours of reperfusion. Gd-DOTA was injected 10 minutes before the dogs were killed. T1 (SE 250/26) and T2 (SE 1500/78) weighted images were performed on excised hearts. Gd-DOTA concentration was measured in myocardium by atomic emission spectrometry, and correlated with myocardial blood flow evaluated by radioactive microspheres. All dogs presented with myocardial infarction (mean size 20.4% +/- 3.1% of the left ventricle), and a corresponding area of increased signal intensity on T1-weighted MR images. In none of the three groups did the area of high signal intensity correlate with the ischemic area. By contrast, after 6 and 48 hours of reperfusion, the high signal intensity area (17.9% +/- 2.4%) closely matched the area of nonreversible jeopardized tissue (16.4% +/- 2.5%), as determined on tetrazolium-stained heart slices. Although a noreflow phenomenon was observed in the jeopardized tissue, Gd-DOTA concentration was higher in the subendocardial central ischemic zone than in normally perfused myocardium. Gd-DOTA imaging enhancement seems to be the consequence of a delayed clearance of the agent from the injured tissue. Gd-DOTA-enhanced MRI accurately quantitates the size of reperfused myocardial infarction on the ex vivo heart for more than 6 hours after the beginning of reperfusion. It remains to be determined whether the in vitro results obtained here can be applied to assess the myocardial infarct size in vivo.