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Representative arterial spin-labeling images for each criterion: extremely
decreased perfusion in the whole brain (asterisk, A); patent external carotid
circulation and the hollow skull sign (arrows, B), and bright vessel signal
intensity around the entry of the carotid artery to the skull (arrows, C). The
darker signal intensity in the bilateral parieto-occipital lobes seems to be due
to the long transit time exceeding that of the postlabeling decay. Scale units:
mL × 100 g−1 × min−1.


CBF maps (scale unit of mL · 100 g−1 · min−1) using ASL of the patient in brain
death (upper row) reveal a severe perfusion defect in the whole brain. Mean
value and standard deviation of CBF measured in the all pixels composing the
gray matter were 7.9 and 3.4 mL · 100 g−1 · min−1. Comparison with normal
intracranial blood flow on ASL images acquired from a 27-year-old medical
school student (bottom row) enhances severely impaired cerebral perfusion in
the patient. CBF indicates cerebral blood flow; ASL, arterial spin labeling.


Representative MR imaging and arterial spin-labeling images in a 50-year-old
man with brain death. Sagittal T1WI (A) shows tonsillar impaction in the
foramen magnum. Axial T2WI (B) reveals gyral swelling with decreased
ventricle size, and DWI (C) shows diffuse hyperintensity involving the whole
brain. Contrast-enhanced MRA (D) shows an abrupt cutoff in the bilateral ICAs
around the entries of carotid arteries to the skull (arrowheads, D) and the
absence of intracranial arterial flow. The ASL images (E–H) satisfy all ASL
criteria supporting brain death: extremely decreased perfusion in the whole
brain (asterisk, F), bright signal intensity in the ICA around the entry of the
carotid artery into the skull suggesting flow stagnation (arrows, G), and patent
external carotid circulation and the hollow skull sign (arrowheads, E). Scale
units: mL × 100 g−1 × min−1.