Imaging and characterization of acute myocardial infarction in vivo by gated nuclear magnetic resonance.

Imaging by nuclear magnetic resonance (NMR) techniques has been shown to provide high-contrast resolution between soft tissues and characterization of normal and pathologic tissues by differences in magnetic relaxation times. The current study was designed to determine whether electrocardiogram (ECG)-gated NMR imaging of the canine heart in vivo could distinguish normal from infarcted myocardium without the use of intravenous paramagnetic contrast agents. Seven dogs were studied by ECG-gated NMR imaging in vivo (spin-echo technique) with a 0.35 Tesla superconducting magnet at 2 to 7 days after ligation of the left anterior descending coronary artery. In six of the seven dogs, signal intensity was increased in the anterior wall compared with the remainder of the left ventricle; this region of high signal intensity corresponded to the area of myocardial infarction demonstrated at postmortem examination. The signal intensity of the infarcted region was 66 +/- 27% greater than that of normal myocardium (p less than .01). The T2 (spin-spin) relaxation time was 69 +/- 3% longer in the infarcted myocardium as compared with normal myocardium (p less than .01). The NMR images from the seventh dog had uniform signal intensity throughout the myocardium of the left ventricle. An infarct was not evident on postmortem examination in this dog. Thus gated NMR imaging in vivo by the spin-echo technique displays acute myocardial infarctions as regions of high signal intensity without the use of contrast media. The infarct is characterized by a prolonged T2 relaxation time.