Diffusion-weighted MR imaging of the normal human spinal cord in vivo

BACKGROUND AND PURPOSE: Diffusion-weighted imaging is a robust technique fo r evaluation of a variety of neurologic diseases affecting the brain, and m ight also have applications In the spinal cord. The purpose of this study w as to determine the feasibility of obtaining in vivo diffusion-weighted ima ges of the human spinal cord, to calculate normal apparent diffusion coeffi cient (ADC) values, and to assess cord anisotropy. METHODS: Fifteen healthy volunteers were imaged using a multi-shot, navigat or-corrected, spin-echo, echo-planar pulse sequence. Axial images of the ce rvical spinal cord were obtained with diffusion gradients applied along thr ee orthogonal axes (6 b values each), and ADC values were calculated for wh ite and gray matter. RESULTS: With the diffusion gradients perpendicular to the orientation of t he white matter tracts, spinal cord white matter was hyperintense to centra l gray matter at all b values. This was also the case at low b values with the diffusion gradients parallel to the white matter tracts; however, at hi gher b values, the relative signal intensity of gray and white matter rever sed. With the diffusion gradients perpendicular to spinal cord, mean ADC va lues ranged from 0.40 to 0.57 x 10(-3) mm(2)/s for white and gray matter. W ith the diffusion gradients parallel to the white matter tracts, calculated ADC values were significantly higher. There was a statistically significan t difference between the ADCs of white versus gray matter with all three gr adient directions. Strong diffusional anisotropy was observed in spinal cor d white matter. CONCLUSION: Small field-of-view diffusion-weighted images of the human spin al cord can be acquired in vivo with reasonable scan times. Diffusion withi n spinal cord white matter is highly anisotropic.