Measurement of myocardial infarct size at early and late time intervals using MR imaging: an experimental study in dogs.

The current study assessed the capability of ECG-gated MR imaging to quantitate both the percentage of the left ventricle involved by acute myocardial infarction and the mass of acute myocardial infarction at 3 and 21 days after coronary occlusion in dogs. Infarct mass was measured from gated transverse MR images using computer-generated calculated-T2 images. T2 images provided accentuation of the boundary between infarcted and normal myocardium as well as objective, reproducible calculation of image voxels representing infarcted myocardium. Postmortem and in vivo MR infarct mass and percentage correlated closely at 3 days (r = .98, SEE = 0.73 g; r = .97, SEE = 1.2%), and 21 days (r = .94, SEE = 1.54 g; r = .95, SEE = 1.61%). Left ventricular mass, infarct mass, and percentage of infarct were measured on end-diastolic MR images. Infarct mass at 3 and 21 days was not significantly different, with a mean deviation of 0.63 g. There was close intra- and interobserver reproducibility (r = .99 and r = .90, respectively) for measurement of infarct mass. The quantitative technique employed for determining the mass of acute myocardial infarctions, based on the different T2 relaxation times of infarcted and normal myocardium, provides for objective analysis and reproducibility. With this technique, MR provides an accurate method for assessing the mass of acute infarcts and the percentage of the left ventricle involved by the infarct both early and late after coronary occlusion.