ON THE NATURE AND REDUCTION OF PLAQUE-MIMICKING FLOW ARTIFACTS IN BLACK BLOOD MRI OF THE CAROTID BIFURCATION

Cardiac-gated black blood MRI of the carotid artery bifurcation in nor mal human subjects shows signal within the lumen suggesting wall thick ening or atherosclerotic plaque. This signal was believed to be artifa ctual, arising from complex flow patterns present at the carotid bifur cation. Computer simulation of the hemodynamics and black blood multis lice image acquisition in a model of the carotid bifurcation showed th at these artifacts arise from spins recovering their signal within the slow, recirculating flow of the carotid bulb. The computed hemodynami cs also suggested that these artifacts could be minimized or eliminate d entirely by gating the acquisition of slices in the most artifact-pr one region of the carotid bulb within a 250-ms window after peak systo le. Application of these predictions to studies of normal volunteers s howed that, in most cases, these flow artifacts in black blood MRI can be eliminated simply by altering the phase of the cardiac cycle to wh ich the image acquisition is gated. The observation that the size and placement of the saturation slabs had little effect on these artifacts suggested that, in those cases in which recirculation persists throug hout the cardiac cycle, either inversion-recovery or presaturation wit hin the bulb itself would be required to suppress them.