Microstructural Characteristics of Cervical Spinal Cord Using High Angular Resolution Diffusion Imaging (HARDI) and Tractography in Healthy Subjects

This study aimed to characterize spinal cord microstructure in healthy subjects using high angular resolution diffusion imaging (HARDI) and tractography.

Forty-nine healthy subjects (18–50 years, divided into 2 age groups) were included in a prospective study. HARDI of the cervical spinal cord were acquired using a 3T MRI scanner with: 64 directions, b‑value: 1000s/mm², reduced field-of-view (zonally magnified oblique multi-slice), and opposed phase-encoding directions. Distortions were corrected using the FSL software package. Fiber tracking was performed using a deterministic approach with DSI-Studio software. Tensor metrics—fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), radial diffusivity (RD)—and tractography statistics were then extracted, at each spine level, and after grey-white matter segmentation.

The microstructural organization of the spinal cord differed between upper and lower cervical spine levels: FA, and AD significantly decreased (p < 0.001); and RD significantly increased (p < 0.05) in lower levels, demonstrating changes in axonal density and myelinated fibers according to a cranio-caudal axis. FA, MD, AD, and RD values were significantly higher in spinal cord white matter (p < 0.0001), compared to grey matter. Age was not associated with a significant change in FA, while there is for MD, AD and RD (p < 0.05). Spinal cord tractography may provide information on the architectural organization of fibers and spinal tracts.

This study proposes a database in cervical spinal cord HARDI, allowing to study the microstructural organization of the spinal cord in healthy subjects, and providing a foundation for comparison with patients presenting spinal cord pathologies.