An in vitro evaluation of the effects of local magnetic-susceptibility-induced gradients on anisotropic water diffusion in nerve

It has been suggested that the anistropy of the water-diffusion coefficient measured in nerve and in white matter could arise from locally anisotropic background gradients induced by the static field, B-0. By utilizing 1) pulse sequences, which minimize the effects of background gradients, and 2) changes in sample orientation, which would maximize the change in the magnitude of these gradients if present, it is shown that in four excised nerves the background gradients do not play a measurable role in the anisotropy of the water-diffusion coefficient at a field strength of 2.35 T. The excised nerves evaluated were the olfactory, trigeminal, and optic nerves of the garfish and the sciatic nerve of the frog.