title: Blue blood or black blood: R1 effects in gradient-echo echo-planar functional neuroimaging.
abstract: Changes in the longitudinal relaxation rate (R1) may play a role in the MRI signal intensity increases that have been associated with physiological brain activation. We used gradient-echo echo-planar MRI (GRE-EPI) to test whether physiological activations associated with hypercapnia in dogs were dependent on the delay (TR) between successive images in a time-series. Our results show that, in addition to activation-induced changes in the R2 (transverse relaxation including inhomogeneity effects), activation-induced changes in R1 are significant under certain pulsing conditions. In our paradigm, the R1 contribution became significant at TR values of 1 s or less.
authors.affiliation: Neuroimaging Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, USA.
authors.forename: A
authors.initials: A
authors.lastname: Righini
authors.forename: C
authors.initials: C
authors.lastname: Pierpaoli
authors.forename: A S
authors.initials: AS
authors.lastname: Barnett
authors.forename: E
authors.initials: E
authors.lastname: Waks
authors.forename: J R
authors.initials: JR
authors.lastname: Alger
mesh_terms: D000818:Animals; D001769:Blood; D001921:Brain / Q000503:physiopathology*; D002560:Cerebrovascular Circulation; D004285:Dogs; D017352:Echo-Planar Imaging; D006935:Hypercapnia / Q000000981:diagnostic imaging / Q000503:physiopathology; D011877:Radionuclide Imaging