Ex Vivo Diffusion Tensor Imaging of Spinal Cord Injury in Rats of Varying Degrees of Severity

Abstract

The aim of this study was to characterize magnetic resonance diffusion tensor imaging (DTI) in proximal regions of the spinal cord following a thoracic spinal cord injury (SCI). Sprague-Dawley rats (n = 40) were administered a control, mild, moderate, or severe contusion injury at the T8 vertebral level. Six direction diffusion weighted images (DWIs) were collected ex vivo along the length of the spinal cord, with an echo/repetition time of 31.6 ms/14 sec and b = 500 sec/mm 2 . Diffusion metrics were correlated to hindlimb motor function. Significant differences were found for whole cord region of interest (ROI) drawings for fractional anisotropy (FA), mean diffusivity (MD), longitudinal diffusion coefficient (LD), and radial diffusion coefficient (RD) at each of the cervical levels ( p < 0.01). Motor function correlated with MD in the cervical segments of the spinal cord (r 2 = 0.80). The diffusivity of water significantly decreased throughout ''uninjured'' portions of the spinal cord following a contusion injury ( p < 0.05). Diffusivity metrics were found to be altered following SCI in both white and gray matter regions. Injury severity was associated with diffusion changes over the entire length of the cord. This study demonstrates that DTI is sensitive to SCI in regions remote from injury, suggesting that the diffusion metrics may be used as a biomarker for severity of injury.

Severity of spinal cord injury influences diffusion tensor imaging of the brain

“…It is possible that Wallerian degeneration alters membrane structures of the brain and that relative changes in intracellular and extracellular water compartments associated with edema may contribute to changes in diffusion. 8 Our study demonstrated a decrease in the diffusion of water in regions of the brainstem associated with the corticospinal tract along with a corresponding increase in the fractional anisotropy. These observations are consistent with an extension of diffusivity changes from the spinal cord into the white matter tracts of the brainstem and brain.…”

“…19 Recently, we have found that there are systemic changes in DTI parameters that occur along the entire length of the spinal cord following an SCI, 20 and that DTI parameter changes correlate to severity of injury up to 10 weeks. 8 Ten weeks has also been used as a time point by other groups. 18,21 At 10 weeks, the initial acute and inflammatory responses have passed; however, inflammatory cells have been found at locations away from the injury site [22][23][24][25] into regions as far from the injury as the brain.…”

“…The 11 week time point was selected to coincide with a prior study examining DTI parameter changes throughout the spinal cord. 8 Animals were euthanized with an IP injection of sodium pentobarbital (100 mg/kg body weight) and perfused through the heart with 300 mL of saline buffer followed by 600 mL of 10% formalin. The brains were excised and postfixed in a 10% formalin solution until the day of scanning.…”

“…34 Degeneration of neural structures has also been associated with changes in diffusion throughout the spinal cord. 8 In previous studies, we have reported changes in diffusion within the cervical spinal cord that differ from diffusion in the thoracic injury zone. In the cervical spinal cord, after a T8 injury in rats, we consistently see a reduced MD.…”

“…In the cervical spinal cord, after a T8 injury in rats, we consistently see a reduced MD. 8 Changes remote from injury suggest an increase in cellularity, possibly due to glial proliferation or other pathological process that results in a decrease in MD. The relative localization to the internal capsule is consistent with an overall degradation of corticospinal tracts.…”