Assessment of myocardial infarct size by means of T2-weighted 1H nuclear magnetic resonance imaging.

Proton (1H) nuclear magnetic resonance (NMR) imaging is thought to depict zones of recent myocardial infarction in contrast to noninfarcted myocardium. This is related to T2 increases in infarct zones that have been verified previously by relaxometry measurements in excised myocardial samples. Accordingly the present study was undertaken to evaluate a 1H NMR imaging method to optimize T2 contrast and measure infarct size in a high-field imaging system (1.5 T). To accomplish this, NMR images were acquired every other R wave with echo times of 30 and 100 msec. The first echo image was used for myocardial border definition and the second echo image, which highlighted the myocardial infarction, for infarct border definition. This T2-weighted approach yielded a significant correlation between infarct size by NMR and pathologic methods. However, NMR imaging tended to overestimate infarct size, and the NMR image depicted abnormal signal well beyond the extent of the pathology-determined infarct. There was a significant relationship between NMR-imaged infarct size and myocardial mass with microsphere-determined reduction in blood flow of 25% or more. These data suggest that T2-weighted NMR imaging depicts not only infarct but also some reversibly injured myocardium.