Ex Vivo Diffusion Tensor Imaging and Quantitative Tractography of the Rat Spinal Cord During Long-term Recovery From Moderate Spinal Contusion

Purpose: To characterize DTI metric changes throughout the length of the entire spinal cord from the acute through chronic stages of spinal cord injury (SCI). Materials and Methods: Ex vivo DTI was performed at 9.4 Tesla to examine changes in water diffusion throughout the entire spinal cord (7-cm) up to 25 weeks after injury in a rat model of contusive SCI. Animals were grouped according to recovery times after injury (2, 5, 15, 20, or 25 weeks), and various DTI metrics were evaluated including transverse and longitudinal apparent diffusion coefficient (tADC and lADC), mean diffusivity (MD), and fractional anisotropy (FA). Results: An overall decrease in lADC throughout the cord and decreases in MD remote from the lesion site were observed, along with an increase in tADC within fiber tracts throughout the recovery period. These trends were statistically significant at P < 0.05 and were found in both white and gray matter regions. tADC and IADC distributions in fiber bundles extracted using DTI tractography were well fit by an exponential model (R = 0.998) with time constants of 4.6 and 3.3 days, respectively. Conclusion: Results from the current study support the hypothesis that the spinal cord undergoes continual changes during recovery from SCI.