Arjen Lindenholz

64 CHAPTER 3 near the vessel wall, which mimics either the vessel wall itself (making it appear thickened) or mimics a focal vessel wall lesion (when flow is focally decreased). These hyperintense artifacts can be present both before and after contrast administration but are in principle more visible after contrast injection ( Figure 6 ). Figure 6. (A and B) 3T precontrast T 1 –weighted vessel wall images (voxel size 0.5 x 0.5 x 1.0 mm 3 ) of a 38-year-old healthy male. (A) An isointense artifact is seen in the lumen of the right ICA (white arrow). (B) A repeated vessel wall sequence within the same scan session did not show the isointense artifact in the lumen (white arrow). (C and D) 3T transverse/oblique postcontrast T 1 -weighted vessel wall images of a 58-year-old healthy male. Hyperintense venous slow flow artifacts are seen in the extracranial veins (white arrow in C ). Hyperintensity caused by slow flow is present in the complete vein, but more prominent along the vessel walls. Slow flow-related hyperintensity can also be observed in the left sigmoid sinus (white arrow in D ). Slow-flow artifacts are most obvious in the slow-flowing blood in smaller and larger veins, for instance in veins within the Sylvian cistern that are in relatively close proximity to the branches of the MCA. When solely interpreting vessel wall images, slow flow in veins can be misinterpreted as arterial wall enhancement. This misinterpretation can be avoided by routinely cross-checking of the location of the intracranial arteries on TOF-MRA images, or by assessing the pattern of