title: Correcting for the echo-time effect after measuring the cerebral blood flow by arterial spin labeling.
abstract: OBJECTIVE
  To take into account the echo time (TE) influence on arterial spin labeling (ASL) signal when converting it in regional cerebral blood flow (rCBF). Gray matter ASL signal decrease with increasing TE as a consequence of the difference in the apparent transverse relaxation rates between labeled water in capillaries and nonlabeled water in the tissue (δR 2*). We aimed to measure ASL/rCBF changes in different parts of the brain and correct them.
  
  
  METHODS
  Fifteen participants underwent ASL measurements at TEs of 9.7-30 ms. Decreases in ASL values were localized by statistical parametric mapping. The corrections assessed were a subject-per-subject adjustment, an average δR 2* value adjustment, and a two-compartment model adjustment.
  
  
  RESULTS
  rCBF decreases associated with increasing TEs were found for gray matter and were corrected using an average δR 2* value of 20 s(-1) . Conversely, for white matter, rCBF values increased with increasing TEs (δR 2* = -23 s(-1)).
  
  
  CONCLUSIONS
  Our correction was as good as using a two-compartment model. However, it must be done separately for the gray and white matter rCBF values because the capillary R 2* values are, respectively, larger and smaller than those of surrounding tissues.
authors.affiliation: UdS, Université de Strasbourg, Strasbourg, France; INSERM U666-Physiopathologie et Psychopathologie Cognitive de la Schizophrénie, Strasbourg, France. jack.foucher@laposte.net
authors.forename: Jack R
authors.initials: JR
authors.lastname: Foucher
authors.forename: Daniel
authors.initials: D
authors.lastname: Roquet
authors.forename: Corinne
authors.initials: C
authors.lastname: Marrer
authors.forename: Bich-Thuy
authors.initials: BT
authors.lastname: Pham
authors.forename: Daniel
authors.initials: D
authors.lastname: Gounot
mesh_terms: D000328:Adult; D001776:Blood Circulation Time; D002533:Cerebral Angiography / Q000379:methods; D002536:Cerebral Arteries / Q000502:physiology; D002540:Cerebral Cortex / Q000098:blood supply; D002560:Cerebrovascular Circulation / Q000502:physiology*; D017352:Echo-Planar Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D018810:Magnetic Resonance Angiography / Q000379:methods*; D008297:Male; D008875:Middle Aged; D008955:Models, Cardiovascular; D009413:Nerve Fibers, Myelinated / Q000502:physiology; D012494:Sampling Studies; D012680:Sensitivity and Specificity; D013113:Spin Labels
chemical_list: D013113:Spin Labels