Fast in vivo high-resolution diffusion MRI of the human cervical spinal cord microstructure

Diffusion Magnetic Resonance Imaging (dMRI) is a widely-utilized method for assessment of microstructural properties in the central nervous system i.e., the brain and spinal cord (SC). In the SC, almost all previous human studies utilized Diffusion Tensor Imaging (DTI), which cannot accurately model areas where white matter (WM) pathways cross or diverge. While High Angular Diffusion Resolution Imaging (HARDI) can overcome some of these limitations, longer acquisition times critically limit its applicability to clinical human studies. In addition, previous human HARDI studies have used limited spatial resolution, with typically a few slices and voxel size ~1 × 1 × 5 mm³ being acquired in tens of minutes. Thus, we have optimized a novel fast HARDI protocol that allows collecting dMRI data at high angular and spatial resolutions in clinically-feasible time. Our data was acquired, using a 3T Siemens Prisma scanner, in less than 9 min. It has a total of 75 diffusion-weighted volumes and high spatial resolution of 0.67 × 0.67 × 3 mm³ (after interpolation in Fourier space) covering the cervical segments C4–C6. Our preliminary results demonstrate applicability of our technique in healthy individuals with good correspondence between low fractional anisotropy (FA) gray matter areas from the dMRI scans, and the same regions delineated on T2-weighted MR images with spatial resolution of 0.35 × 0.35 × 2.5 mm³. Our data also allows the detection of crossing fibers that were previously shown in vivo only in animal studies.