title: Quantification of BOLD fMRI parameters to infer cerebrovascular reactivity of the middle cerebral artery.
abstract: OBJECTIVE
  To quantify the amplitude and temporal aspects of the blood oxygenation level-dependent (BOLD) response to an auditory stimulus during normocapnia and hypercapnia in healthy subjects in order to establish which BOLD parameters are best suited to infer the cerebrovascular reactivity (CVR) in the middle cerebral artery (MCA) territory.
  
  
  METHODS
  Twenty healthy volunteers (mean age: 23.6 ± 3.7 years, 11 women) were subjected to a functional paradigm composed of five epochs of auditory stimulus (3 sec) intercalated by six intervals of rest (21 sec). Two levels of hypercapnia were achieved by a combination of air and CO2 while the end-tidal CO2 (ETCO2 ) was continually measured. An autoregressive method was applied to analyze four parameters of the BOLD signal: onset-time, time-to-peak, full-width-at-half-maximum (FWHM), and amplitude.
  
  
  RESULTS
  BOLD onset time (P < 0.001) and full-width at half-maximum (FWHM) (P < 0.05) increased linearly, while BOLD amplitude decreased (P < 0.001) linearly with increasing levels of hypercapnia. Test-retest for reproducibility in five subjects revealed excellent concordance for onset time and amplitude.
  
  
  CONCLUSIONS
  The robust linear dependence of BOLD onset time, FWHM, and amplitude to hypercapnia suggest future application of this protocol in clinical studies aimed at evaluating CVR of the MCA territory.
authors.affiliation: Department of Neuroscience and Behavioural Sciences, FMRP, University of Sao Paulo, Ribeirao Preto, Brazil.
authors.forename: Kelley C
authors.initials: KC
authors.lastname: Mazzetto-Betti
authors.forename: Renata F
authors.initials: RF
authors.lastname: Leoni
authors.forename: Octavio M
authors.initials: OM
authors.lastname: Pontes-Neto
authors.forename: Marcio J
authors.initials: MJ
authors.lastname: Sturzbecher
authors.forename: Antonio C
authors.initials: AC
authors.lastname: Santos
authors.forename: Joao P
authors.initials: JP
authors.lastname: Leite
authors.forename: Afonso C
authors.initials: AC
authors.lastname: Silva
authors.forename: Draulio B
authors.initials: DB
authors.lastname: de Araujo
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity; D001931:Brain Mapping / Q000379:methods*; D002560:Cerebrovascular Circulation; D005260:Female; D006801:Humans; D006935:Hypercapnia / Q000503:physiopathology*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D020768:Middle Cerebral Artery / Q000503:physiopathology*; D010101:Oxygen Consumption; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity