Evaluation of myocardial ischemia and infarction by nuclear magnetic resonance techniques

Proton NMR imaging of myocardial ischemia without infarction requires the use of paramagnetic contrast agents. Even during the first few hours of infarction, imaging without contrast enhancement reveals only slight natural image contrast. Myocardial infarction, however, is much more readily detected during the first few days and weeks post coronary occlusion; this is due to a marked elevation in T2 during this time period. Chronic infarction, several months after the acute event, does not demonstrate altered signal intensity, but can be detected by visualizing myocardial wall thinning and aneurysm formation. Information regarding high energy phosphate metabolism can be acquired in vivo in ischemic animal preparations; preliminary data has demonstrated that it is possible to acquire similar information noninvasively in man. Development of this technique will eventually permit the study of pharmacological and mechanical interventions aimed at preserving myocardium in the ischemic heart. Exogenous labelling of myocardial tissue with carbon-13 permits the study of the effects of substrates on cellular metabolism. Ultimately, the technique of chemical shift imaging will provide a method of spatially resolving valuable metabolic information in the form of an NMR image. Eventually, with the gradual development of NMR technology, imaging and spectroscopy will become truly important clinical tools in the investigation of ischemic heart disease in man.