Artifacts from pulsatile flow in MR imaging.

Previous investigators have examined the effect of blood flow on the apparent blood vessel signal intensity. These studies reported flow brightening and darkening effects within vessels. In this paper we have investigated another type of flow artifact, which originates from the pulsatile nature of blood flow. These flow artifacts have characteristic bright and dark "ghosting" patterns which appear close to small vessels, usually arteries, which are bright in slow flow. Similar to the amplitude-of-motion artifacts caused by patient motion (e.g., breathing and cardiac motion) the ghosting artifacts due to pulsatile flow are best characterized as frequency modulated spectral sidebands. The pulsatile artifacts can have both dark and bright structures and usually appear close to the "moving" vessel that generates the artifact. In this paper we present a study of the chief features of these pulsatile flow artifacts, and we develop a theoretical description of their origins in terms of "accidental" velocity-encodings that occur strongly in most magnetic resonance imaging sequences.