title: Optimized simultaneous ASL and BOLD functional imaging of the whole brain.
abstract: OBJECTIVE
  To compare a double-excitation combined arterial-spin labeling/blood-oxygenation level dependent (ASL/BOLD) functional imaging method to a double-echo method. ASL provides a useful complement to standard BOLD functional imaging, to map effects of cerebral hemodynamics. Whole-brain imaging is necessary to properly characterize large functional networks. A challenge of whole-brain ASL/BOLD is that images for ASL functional contrast must be acquired before significant longitudinal relaxation of the inverted spins occurs; however, a longer echo time (TE) is required for optimal BOLD functional contrast, lengthening the acquisition time. Thus, existing combined ASL/BOLD studies have only partial-brain coverage.
  
  
  METHODS
  The proposed method allows acquisition of images for ASL contrast within a short period after the ASL labeling pulse and postinversion delay, then subsequent acquisition of images with longer TE for BOLD contrast. The technique is demonstrated using a narrative comprehension task in 35 normal children, and the double-excitation method is empirically compared with the double-echo method in 7 normal adults.
  
  
  RESULTS
  Compared with a double-echo sequence, simulations show the double-excitation method improves ASL contrast-to-noise ratio (CNR) (∼50%) in later-acquired slices with minimal (<1%) reduction in BOLD CNR in earlier-acquired slices if reduced excitation flip angles for the ASL acquisitions are used. Empirical results from adult data are in agreement with the simulations. Group analyses from the narrative comprehension task also show greater intersubject sensitivity in BOLD versus ASL.
  
  
  CONCLUSIONS
  Our method simultaneously optimizes ASL and BOLD acquisitions for CNR while economizing acquisition time.
authors.affiliation: Cincinnati Children's Hospital Medical Center, Pediatric Neuroimaging Research Consortium, Cincinnati, Ohio, USA; Children's Hospital of Pittsburgh of UPMC, Dept. of Radiology, Pittsburgh, Pennsylvania, USA.
authors.forename: Vincent J
authors.initials: VJ
authors.lastname: Schmithorst
authors.forename: Luis
authors.initials: L
authors.lastname: Hernandez-Garcia
authors.forename: Jennifer
authors.initials: J
authors.lastname: Vannest
authors.forename: Akila
authors.initials: A
authors.lastname: Rajagopal
authors.forename: Greg
authors.initials: G
authors.lastname: Lee
authors.forename: Scott K
authors.initials: SK
authors.lastname: Holland
mesh_terms: D000293:Adolescent; D000465:Algorithms; D001783:Blood Flow Velocity / Q000502:physiology; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping / Q000379:methods; D002560:Cerebrovascular Circulation / Q000502:physiology*; D002648:Child; D002675:Child, Preschool; D032882:Comprehension / Q000502:physiology*; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D007807:Language Tests; D018810:Magnetic Resonance Angiography / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D064847:Multimodal Imaging / Q000379:methods; D010092:Oximetry / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013113:Spin Labels
chemical_list: D013113:Spin Labels
keywords: BOLD functional imaging; arterial spin labeling; pediatric neuroimaging