Magnetic Resonance Imaging for Area at Risk, Myocardial Infarction, and Myocardial Salvage

Almost all published preclinical studies of cardioprotective agents include a measurement of area at risk, infarct size, and thus allow determination of myocardial salvage as an indicator of therapeutic benefit. Until recently, single-photon emission tomography (SPECT) imaging with injection of sestamibi prior to intervention was the only clinical method suitable for making similar assessments in patients. Over the past 5 years, a large number of articles have documented that magnetic resonance imaging (MRI) can noninvasively determine area at risk, infarct size, and myocardial salvage. While T2-weighted imaging has been the method used most commonly, precontrast T1-weighted images and early gadolinium enhancement (EGE) images can also determine the size of the area at risk. All 3 of these MRI methods detect the area at risk based on myocardial edema resulting from ischemia. Late gadolinium enhancement (LGE) images provide a well-accepted reference standard for infarct size in all of those methods. Finally, LGE images can also provide a single modality measure of myocardial salvage based on the "wave front" of myocardial injury associated with the progressively more severe damage associated with acute myocardial infarction (MI). Essentially, the LGE images can provide an endocardial-based snap shot of infarct size and salvaged myocardium is estimated as the viable myocardium within the circumferential extent of the infarct. Thus, the purpose of this review is to provide an overview of how MRI can determine the area at risk, infarct size, and thus measure myocardial salvage.