In most instances, imaging studies are performed with contrast enhancement (iodine-based for CT, gadolinium-based for MRI), which is injected through a small intravenous access in an arm vein. CT scans are used primarily to evaluate vascular structures, such as the coronary arteries or the aorta and its branch vessels. The primary strength of MRI is tissue characterization and its ability to evaluate the heart muscle for function, perfusion and viability. MRI is also helpful in valvular and congenital heart disease.
Typically, a CT scan, which uses x-ray technology, takes 10-20 seconds to perform. The patient will spend about 20 minutes in the CT scanner suite. Complete cardiovascular MRI studies typically require about 40 minutes. Common reasons for performing CT studies are known or suspected narrowing or blockage of coronary arteries, renal arteries, or mesenteric arteries, and diseases of the aorta (dissection, aneurysm). In some patients CT scans may be a good alternative to cardiac catheterization for non-invasive evaluation of the heart vessels patency. Typical reasons for performing MR studies include known or suspected congenital cardiovascular anomalies, cardiac valve abnormalities, or evaluation of coronary artery disease by assessing cardiac function, perfusion and the amount of viable heart tissue prior to bypass surgery. MR can also be used to diagnose diseases of the aorta and its branch vessels as well as the vasculature of the upper and lower extremity for known or suspected peripheral vascular disease.