Optimization of a single-shot EPI sequence for diffusion imaging of the human spinal cord

Diffusion weighted imaging (DWI) and diffusion tensor imaging (DTI) are established techniques of magnetic resonance widely used for the characterization of the cerebral tissue. Despite the successful application in the brain, diffusion-weighted single-shot echo-planar-imaging (EPI) of the spinal cord is hindered by the need for highly-resolved spatial encoding in an area of strong magnetic field inhomogeneities, and the shortness of transverse relaxation time. The major aim of this study was the optimization of a reliable single-shot EPI sequence for DTI of the spinal cord at 1.5T. Ten healthy volunteers participated in the study (mean age=28.4±3.1). A single-shot EPI sequence with double spin-echo diffusion preparation and nominal in-plane resolution of 0.9×0.9mm ² was optimized with regard to cerebrospinal fluid artifacts, and contrast-to-noise ratio between gray matter (GM) and white matter (WM). The effective sequence resolution was evaluated on a phantom. A cardiac-pulse gated sequence with optimal matrix size (read × phase=64×32) and b-value (700s/mm ²) allowed for the acquisition of highly-resolved images of the spinal cord (effective in-plane resolution= 1.1mm). Preliminary results on two healthy volunteers showed that the butterfly-shaped GM is clearly recognizable in the reconstructed fractional anisotropy (FA) maps. Measured WM FA values were 0.698±0.076 and 0.756±0.046. No significant differences were found in the mean diffusivity computed in the WM as compared to the GM areas. Optimized spinal cord diffusion imaging provided promising preliminary results on healthy volunteers. The application of the proposed protocol in the assessment of neurological disorders may allow for improved characterization of healthy and impaired WM and GM.