Cardiovascular disease is a leading cause of morbidity and mortality worldwide. Many novel imaging methods have been developed to study atherosclerosis in patients suffering from coronary artery disease (CAD). Imaging techniques that will allow identifying progressive cardiac disease and prediction of future clinical risk are becoming of more and more importance.

In addition to echocardiography, cardiac magnetic resonance imaging (MRI) might be used for the noninvasive assessment of LV volumes and LVEF in a heart failure setting. One of the main advantages of cardiac MRI over other imaging modalities is its ability to assess changes in tissue. For example by using contrast-enhanced pulse sequences cardiac MRI can be used to assess myocardial viability. This technique has displayed high diagnostic accuracy for acute inflammatory or ischemic injury.

Nowadays, late gadolinium enhancement (LGE) imaging has become the primary diagnostic tool for assessment of myocardial viability in patients suffering from CAD. With LGE, hypo- or akinetic but still viable myocardium can be identified as dysfunctional myocardium without scar or significant remaining viable tissue (<50% transmurality of scarring). In clinical practice this additional information will help to decide whether or not the patient will recover after revascularization.

The mechanism of LGE in acute and chronic infarction is the increase in the extracellular space caused by necrosis (loss of cell membrane integrity) with the former and the larger extracellular space of scar compared to myocardium with the latter. Magnetic resonance contrast agent that diffused to the interstitial space will be resorbed into the capillary bed and undergo renal excretion. However, when the tissue is damaged, for example, due to infarction, diffuse fibrosis or even inflammation, the resorption rate of contrast agent will be diminished. At 10-20 min after contrast injection, washout will be complete in normal myocardium in contrast to infarcted or edematous tissue. This phenomenon is the basis of “late gadolinium enhancement” imaging.

Various studies have shown the relation between myocardial viability and the size of the area displaying late gadolinium enhancement. In MR images, the presence of contrast agent can be detected as a bright area on images acquired with T1-weighted MR images. Moreover, a strong correlation between the transmural extent of LGE and regional function recovery has been demonstrated in several studies, revealing LGE imaging as a powerful predictor of myocardial damage after myocardial infarction. While the distribution of LGE is invariably subendocardial for ischemic disease (either acute or chronic myocardial infarction), the pattern of enhancement has a variable transmural distribution in non-ischemic myocardial disease. In ischemic heart disease LGE conforms to the distribution of one or more coronary arteries.

Microvascular obstruction (MO) or the “no-reflow” phenomenon is an established complication of coronary reperfusion therapy. It is increasingly recognized as a poor prognostic indicator and can serve as an imaging marker of subsequent adverse LV remodeling. Although MO can be assessed using various imaging modalities, evaluation by cardiac MRI is particularly useful in enhancing its detection, diagnosis, and quantification, as well as following its subsequent effects on infarct evolution and healing. MO assessment has become a routine component of the MR evaluation of acute myocardial infarction and will increasingly play a role in therapeutic decision pathways.

MO is characterized by a number of ultrastructural and functional changes at the microvascular level. Understanding these histopathophysiologic changes can inform the approach by MRI to detecting MO, to understand the results and their subsequent clinical implications. It can also help potentially improve how MO is assessed by CMR which has implications with regard to the understanding of infarct evolution as well as the evaluation of the efficacy and mechanism of reperfusion treatment.

MO has been found to be predictive of clinical outcome, independently of or when adjusted for other indices such as infarct size and LV ejection fraction (EF).Many of these outcome studies showed a severe relationship between presence of MO and adverse LV remodeling with reduced global systolic function and larger LV volumes at follow-up exams, suggesting a possible mechanism for the poor prognosis.