Figure 3.

Cerebrospinal fluid (CSF) labelling artefact. Axial arterial spin labelling (ASL) fluid-attenuated inversion recovery (FLAIR) sequence fused and unfused ASL image (a) and (c), respectively, showing the increased peri-medullary CSF bright red signal (shown by white arrowhead), which is also demonstrated in the sagittal reformatted FLAIR ASL fused image (white arrowhead in (b)).The axial ASL image (d) in a different patient showing the partial ring of fire artefact, seen as a high signal in the right cerebello-medullary and cerebello-pontine cistern (white arrowhead). Sagittal reformat showing the craniocaudal smearing (arrowheads in (e)). After relocating the labelling plane the artefact is eliminated (sagittal reformat (f)).