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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