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Mean pCASL-CBF maps for the left-sided cases of the three most prevalent posterior circle of Willis variants. A reduction in pCASL-CBF signal can be seen on the posterior side contralateral to the fetal-type posterior cerebral artery. Fetal hyp. P1: fetal variant with hypoplastic ipsilateral P1 segment; Fetal no P1: fetal variant lacking the ipsilateral P1 segment.
