title: Invited commentary.
authors.affiliation: Division of Cardiothoracic Surgery, University of Pittsburgh School of Medicine, 200 Lothrop St, UPMC-Presbyterian C-718, Pittsburgh, PA15213, USA. gleasontg@upmc.edu
authors.forename: Thomas G
authors.initials: TG
authors.lastname: Gleason
mesh_terms: D002560:Cerebrovascular Circulation / Q000502:physiology*; D002941:Circle of Willis / Q000000981:diagnostic imaging* / Q000502:physiology*; D003097:Collateral Circulation / Q000502:physiology; D006801:Humans; D020768:Middle Cerebral Artery / Q000000981:diagnostic imaging* / Q000502:physiology*; D010477:Perfusion / Q000379:methods; D012039:Regional Blood Flow; D017585:Ultrasonography, Doppler, Transcranial