Magnetic resonance measurement of velocity and flow: technique, validation, and cardiovascular applications

With a newly developed magnetic resonance (MR) technique for blood flow measurements, qualitative and quantitative information on both flow volume and flow velocity in the great vessels can be obtained. MR flow quantitation is performed with a gradient-echo MR sequence with high temporal resolution enabling measurements at frequent intervals throughout the cardiac cycle. MR flow quantitation uses the phase rather than the amplitude of the MR signal to reconstruct the images. These images, often referred to as MR velocity maps or velocity-encoded cine MR images, are two-dimensional displays of flow velocity. From these velocity maps, velocity and volume flow data can be obtained. Previous validation experiments have demonstrated the accuracy of MR velocity mapping, and this technique is now being applied successfully in several clinical fields. MR velocity mapping may be of considerable value when Doppler echocardiography results are unsatisfactory or equivocal, particularly because MR is suited for the analysis of volumetric flow and complex flow patterns. Among the vastly growing number of clinical cardiovascular applications that have been reported are the great arteries and veins, coronary vessels, valvular disease, and the abdominal and peripheral vessels. These items are reviewed, and some aspects of the technique that need improvement are discussed.