Conditions for quantitative evaluation of injured spinal cord by in vivo diffusion tensor imaging and tractography: Preclinical longitudinal study in common marmosets

Convent ional magnet ic resonance imaging (MRI) can detect hemorrhage, edema, syrinx, and spinal cord atrophy, but not axonal disrupt ion after spinal cord injury (SCI). We previously demonstrated that diffusion tensor t ractography (DTT) could depict axonal disrupt ion after hemisect ion SCI in common marmosets. In the present study, to determine the relat ionship between DTT results and funct ional recovery after contusive SCI, we performed longitudinal DTT, behavioral, and histological analyses before and after contusive SCI in common marmosets. By comparing the tract fiber est imate depicted by DTT with neuronal fibers labeled with RT97 and SMI-31, ant i-neurofilament ant ibodies, we determined the opt imal fract ional anisotropy (FA) threshold for fiber t racking to be 0.40. The rat io of the number of t ract fiber est imate at the lesion site to the number before SCI, determined by DTT, was significant ly correlated with the funct ional recovery after SCI. Moreover, comparison of the longitudinal preand post-SCI FA and axial diffusivity (λ( )) values revealed that they decreased after injury at the sites caudal to the lesion epicenter in the cort icospinal t ract and rostral to the lesion epicenter in the dorsal column. The FA values, then, showed part ial recovery in the dorsal column. FA-value-oriented color DTT was used to represent axonal sparing or regenerat ion of the different t racts. These findings indicated that DTT analysis might be a versat ile noninvasive tool for evaluat ing the axonal disrupt ion after SCI.