Blue blood or black blood: R1 effects in gradient-echo echo-planar functional neuroimaging.
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.
Righini
A
A
Neuroimaging Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, USA.
Pierpaoli
C
C
Barnett
A S
AS
Waks
E
E
Alger
J R
JR
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