T1-selective diffusion weighted fMRI at 1.5 T
Apparent diffusion coefficients (ADC) of protons contributing to the functional signal can be determined from diffusion weighted functional magnetic resonance imaging (MRI) studies. An earlier study indicated that ADCs calculated from the functional signal of an activated primary sensorimotor cortex are large, and consistent with a CSF or intravascular contribution to the functional signal. We have added inversion recovery pulses to isotropic diffusion weighted imaging to null CSF protons selectively within the imaging slice, or to null the outer volume blood flowing into the imaging slice. With the use of gradient recalled diffusion weighted echo-planar imaging at low gradient b factors, and without the use of inversion pulses, the ADCs×103 in mm2/s (±SD) from the functional signal were 6.81±1.19. These ADCs were significantly higher than resting primary sensorimotor cortex ADCs of 2.26±1.49, measured at the same b factors. When CSF nulling was applied, the functional signal ADCs remained high. Application of inflow nulling decreased the functional signal to such a small value, that ADCs estimated from these functional signals were not assessed. The results are consistent with an intravascular contribution to the functional signal and to its large ADC
