Viability
Assessment of myocardial viability following a myocardial infarction is perhaps the most frequent indication for requesting a Cardiac MR. Viability studies are based on delayed enhancement imaging. Approximately 10 minutes following contrast administration, areas of infarcted myocardium are noted to “hyperenhance” relative to the normal myocardium. This hyperenhancement represents the accumulation of gadolinium in the extracellular space, due to the loss of membrane integrity in the infarcted tissue.
Cardiac MR viability studies allow for detailed assessment of a myocardial infarction. It allows an accurate description of the location and size of the infarct, including the vascular distribution of the coronary artery territories involved. More importantly, Cardiac MR can also assess the transmural extent of the infarct – a significant factor in considering a patient for a revascularization procedure.
Viability images are compared with cine functional studies to evaluate for wall motion abnormalities. Studies can also demonstrate complications associated with infarcts, including intracardiac thrombus or left ventricular aneurysms.
Post-processing using ARGUS software allows for calculation of left ventricular ejection fraction following myocardial infarction.