Velocity-encoded cine MR imaging in aortic coarctation: functional assessment of hemodynamic events.

Velocity-encoded cine magnetic resonance (MR) imaging is becoming the modality of choice for the clinical evaluation of aortic coarctation, a congenital narrowing of the thoracic aorta, in which a functional assessment of hemodynamic obstruction is as important as anatomic delineation. A flow-sensitive phase-contrast technique, velocity-encoded cine MR imaging is based on the principle that moving protons change phase in proportion to their velocity. Because it enables precise hemodynamic characterization, the technique is especially useful for evaluating the severity of aortic coarctation. By enabling a qualitative assessment of the presence and direction of collateral circulation, velocity-encoded cine MR imaging provides information about the presence and severity of obstruction. It also allows accurate quantitation of key hemodynamic parameters such as flow velocity, flow volume, and pressure gradients across the coarctation-functional information that is clinically useful for both preoperative planning and postinterventional monitoring. The results of recent experience indicate that velocity-encoded cine MR imaging also may be applicable for the detection of recurrent stenosis after stent placement or angioplasty.