Histological correlation of diffusion tensor imaging metrics in experimental spinal cord injury

Abstract

Diffusion tensor imaging (DTI) has the potential to provide important information about the integrity of white matter tracts in injured spinal cord tissue. It is thought that DTI‐based transverse diffusivity (λ_t) reflects the state of myelin, whereas longitudinal diffusivity (λ_l) reflects axonal integrity. However, this has not been established in spinal cord injury (SCI). Therefore, we performed quantitative histologic analysis on 4‐ and 8‐week post‐SCI rodent spinal cords that had received a moderately severe injury at the T7 level and correlated the histology with λ_t and λ_l measured in vivo. Using antibodies specific to myelin and axonal process (i.e., neurofilament), the percent area of expression was determined in the dorsal, ventral, and lateral white matter from both rostral and caudal regions away from the epicenter of the injury site. The results suggest a positive correlation between λ_t and demyelination in many but not all regions. However, these studies failed to establish a correlation between λ_l and axonal damage. These results suggest that caution must be exercised in interpreting the DTI metrics in terms of tissue pathology in SCI.