The appearance of rapidly flowing blood on magnetic resonance images.

The appearance of rapidly flowing blood on imaging (MRI) was evaluated using flow phantoms and dye infusion experiments. Laminar flow can be maintained at high velocities in small-diameter vessels. Under such conditions, flow-related enhancement may be observed several slices into a multislice imaging volume. Decreasing cross-sectional area of the unsaturated protons in the midstream is noted on slices further removed from the entry surface. As the velocity increases, turbulence occurs. The increased random motion of the protons causes loss of intensity on the first-echo image, although rephasing with increased intensity can be noted on the second-echo image. The flow pattern of a simple intraluminal obstruction is demonstrated by MRI and dye infusion experiments. Rephasing is noted within the eddy downstream from the obstruction. Clinical examples of the phantom findings are shown and applications are discussed.