Cerebral ArteriesCollateral CirculationMagnetic Resonance AngiographyNeuroendoscopyCarotid Artery, InternalCerebrovascular CirculationMoyamoya DiseaseCerebral AngiographyDoppler EffectAngiography, Digital SubtractionHistory, 17th CenturyIntracranial ArteriosclerosisUltrasonography, Doppler, TranscranialBasilar ArteryVertebral ArteryIntracranial AneurysmSphenoid BoneCarotid StenosisCarotid Artery, ExternalArachnoidEchoencephalographyCarotid-Cavernous Sinus FistulaMigraine with AuraCranial Fossa, PosteriorOphthalmic ArteryIntracranial Arteriovenous MalformationsSkull BaseCircle of WillisBlood Flow VelocityCerebral InfarctionPia MaterCerebrovascular DisordersDominance, CerebralBrain IschemiaBrainSubarachnoid HemorrhageUltrasonography, Doppler, ColorIschemic Attack, TransientArterial Occlusive DiseasesImaging, Three-DimensionalCarotid ArteriesCarotid Artery DiseasesCadaverImage Processing, Computer-AssistedEndarterectomy, CarotidTomography, X-Ray ComputedContrast MediaUltrasonographyStrokeRegional Blood FlowReference ValuesSensitivity and SpecificityProspective Studies