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The COW consists of A-COW and P-COW sections. A-COW in red: bilateral A1 segments of ACA and ACoA. P-COW in blue: bilateral P1 segments of PCA and bilateral PCoAs. ACA, anterior cerebral artery; ACoA, anterior communicating artery; BA, basilar artery; COW, circle of Willis; A-COW, anterior COW; P-COW, posterior COW; MCA, middle cerebral artery; PCA, posterior cerebral artery; PCoA, posterior communicating artery; VA, vertebral artery.
