BLUE-BLOOD OR BLACK BLOOD - R(1) EFFECTS IN GRADIENT-ECHO ECHO-PLANARFUNCTIONAL NEUROIMAGING

Changes in the longitudinal relaxation rate (R(1)) may play a role in the MRI signal intensity increases that have been associated with phys iological brain activation, We used gradient-echo echo-planar MRI (GRE -EPI) to test whether physiological activations associated with hyperc apnia in dogs were dependent on the delay (TR) between successive imag es in a time-series, Our results show that, in addition to activation- induced changes in the R(2) (transverse relaxation including inhomoge neity effects), activation-induced changes in R(1) are significant und er certain pulsing conditions. In our paradigm, the R(1) contribution became significant at TR values of 1 s or less.