title: Cerebrovascular reactivity measured with arterial spin labeling and blood oxygen level dependent techniques.
abstract: OBJECTIVE
  To compare cerebrovascular reactivity (CVR) quantified with pseudo-continuous arterial spin labeling (pCASL) and blood oxygen level dependent (BOLD) fMRI techniques.
  
  
  METHODS
  Sixteen healthy volunteers (age: 37.8±14.3years; 6 women and 10 men; education attainment: 17±2.1years) were recruited and completed a 5% CO2 gas-mixture breathing paradigm at 3T field strength. ASL and BOLD images were acquired for CVR determination assuming that mild hypercapnia does not affect the cerebral metabolic rate of oxygen. Both CVR quantifications were derived as the ratio of the fractional cerebral blood flow (CBF) or BOLD signal change over the change in end-tidal CO2 pressure.
  
  
  RESULTS
  The absolute CBF, BOLD and CVR measures were consistent with literature values. CBF derived CVR was 5.11±0.87%/mmHg in gray matter (GM) and 4.64±0.37%/mmHg in parenchyma. BOLD CVR was 0.23±0.04%/mmHg and 0.22±0.04%/mmHg for GM and parenchyma respectively. The most significant correlations between BOLD and CBF-based CVRs were also in GM structures, with greater vascular response in occipital cortex than in frontal and parietal lobes (6.8%/mmHg versus 4.5%/mmHg, 50% greater). Parenchymal BOLD CVR correlated significantly with the fractional change in CBF in response to hypercapnia (r=0.61, P=0.01), suggesting the BOLD response to be significantly flow driven. GM CBF decreased with age in room air (-5.58mL/100g/min per decade for GM; r=-0.51, P=0.05), but there was no association of CBF with age during hypercapnia. A trend toward increased pCASL CVR with age was observed, scaling as 0.64%/mmHg per decade for GM.
  
  
  CONCLUSIONS
  Consistent with previously reported CVR values, our results suggest that BOLD and CBF CVR techniques are complementary to each other in evaluating neuronal and vascular underpinning of hemodynamic processes.
authors.affiliation: Department of Radiology, University of Pennsylvania, Philadelphia, PA 19104. Electronic address: zhouyong@mail.med.upenn.edu.
authors.forename: Yongxia
authors.initials: Y
authors.lastname: Zhou
authors.affiliation: Department of Radiology, University of Pennsylvania, Philadelphia, PA 19104.
authors.forename: Zachary B
authors.initials: ZB
authors.lastname: Rodgers
authors.affiliation: Department of Radiology, University of Texas South Medical Center, San Antonio, TX.
authors.forename: Anderson H
authors.initials: AH
authors.lastname: Kuo
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity / Q000502:physiology; D001921:Brain / Q000098:blood supply* / Q000502:physiology; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D013113:Spin Labels
chemical_list: D013113:Spin Labels
keywords: Arterial spin labeling; BOLD; Cerebral blood flow; Cerebrovascular reactivity; Hypercapnia-based fMRI calibration; Neurovascular coupling