The role of MR imaging in the evaluation of acquired diseases of the thoracic aorta.

Because MR imaging combines the major attributes of angiography, echocardiography, and CT, its role in the evaluation of the thoracic aorta is steadily increasing. When standard spin-echo techniques are used, flowing blood produces a signal void that allows excellent depiction of the anatomy and simultaneous evaluation of the lumen, vessel wall, and periaortic structures. On dynamic or cine MR, flowing blood generates a signal that allows visualization of the blood as it pulsates through the aorta. Turbulent blood generates a signal void, thereby allowing the detection and qualitative assessment of the pathophysiologic consequences of anatomic abnormalities. With phase-mapping techniques, blood velocity can be measured and used to calculate pressure gradients. Recent advances in the field of MR angiography will greatly enhance the overall role of MR in the evaluation of the thoracic vasculature by allowing detection and assessment of the branch vessels. Although the technique is still evolving, it has shown extraordinary potential as a tool for studying the thoracic aorta. The exact role of MR in patient care will depend on advances in transesophageal echocardiography. However, it is not unreasonable to think that someday MR imaging will be the primary technique for evaluation of the thoracic aorta.