title: Noninvasive MRI measurement of the absolute cerebral blood volume-cerebral blood flow relationship during visual stimulation in healthy humans.
abstract: OBJECTIVE
  The relationship between cerebral blood volume (CBV) and cerebral blood flow (CBF) underlies blood oxygenation level-dependent functional MRI signal. This study investigates the potential for improved characterization of the CBV-CBF relationship in humans, and examines sex effects as well as spatial variations in the CBV-CBF relationship.
  
  
  METHODS
  Healthy subjects were imaged noninvasively at rest and during visual stimulation, constituting the first MRI measurement of the absolute CBV-CBF relationship in humans with complete coverage of the functional areas of interest.
  
  
  RESULTS
  CBV and CBF estimates were consistent with the literature, and their relationship varied both spatially and with sex. In a region of interest with stimulus-induced activation in CBV and CBF at a significance level of the P < 0.05, a power function fit resulted in CBV = 2.1 CBF(0.32) across all subjects, CBV = 0.8 CBF(0.51) in females and CBV = 4.4 CBF(0.15) in males. Exponents decreased in both sexes as ROIs were expanded to include less significantly activated regions.
  
  
  CONCLUSIONS
  Consideration for potential sex-related differences, as well as regional variations under a range of physiological states, may reconcile some of the variation across literature and advance our understanding of the underlying cerebrovascular physiology.
authors.affiliation: Department of Biomedical Engineering, Yale University, School of Medicine, Magnetic Resonance Research Center, New Haven, Connecticut, USA.
authors.forename: Pelin Aksit
authors.initials: PA
authors.lastname: Ciris
authors.forename: Maolin
authors.initials: M
authors.lastname: Qiu
authors.forename: R Todd
authors.initials: RT
authors.lastname: Constable
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity / Q000502:physiology*; D001810:Blood Volume / Q000502:physiology*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D010775:Photic Stimulation
keywords: Grubb's relationship; blood oxygenation level-dependent; brain activation; cerebral blood flow; cerebral blood volume; functional MRI; visual stimulation