T-1-selective diffusion weighted fMRI at 1.5 T

Apparent diffusion coefficients (ADC) of protons contributing to the functi onal signal can be determined from diffusion weighted functional magnetic r esonance imaging (MRI) studies. An earlier study indicated that ADCs calcul ated 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 dif fusion weighted imaging to null CSF protons selectively within the imaging slice, or to null the outer volume blood flowing into the imaging slice. Wi th the use of gradient recalled diffusion weighted echo-planar imaging at l ow gradient b factors, and without the use of inversion pulses, the ADCs x 10(3) in mm(2)/s (+/- SD) from the functional signal were 6.81 +/- 1.19. Th ese ADCs were significantly higher than resting primary sensorimotor cortex ADCs of 2.26 +/- 1.49, measured at the same b factors. When CSF nulling wa s applied, the functional signal ADCs remained high. Application of inflow nulling decreased the functional signal to such a small value, that ADCs es timated from these functional signals were not assessed. The results are co nsistent with an intravascular contribution to the functional signal and to its large ADC. (C) 1998 John Wiley & Sons, Ltd.