An in vivo evaluation of the effects of local magnetic susceptibility-induced gradients on water diffusion measurements in human brain

The effect of possible susceptibility-induced gradients on measurements of water diffusion along the transverse and longitudinal axes of white matter fibers in the brain was investigated in vivo at 1.5 T, Measurements obtaine d with sequences sensitive and insensitive, respectively, to susceptibility -induced gradients indicated that these gradients do not contribute signifi cantly to diffusion anisotropy in brain white matter. Furthermore, diffusio n measurements were unaffected by the presence of known susceptibility-indu ced gradients at the interface between the petrous bone and brain parenchym a. These results agree with those obtained on in vitro samples and appear t o support the hypothesis that interactions between the diffusing water mole cules and the cellular environment constitute the principal mechanism for d iffusion anisotropy in brain white matter at 1.5 T. This, in turn, simplifi es the interpretation of diffusion time-dependent measurements in terms of membrane separation and permeability. (C) 1999 Academic Press.