Diffusion tensor imaging eigenvalues: Preliminary evidence for altered myelin in cocaine dependence

Reduced fractional anisotropy (FA) in Diffusion Tensor Imaging (DTI) has been reported in cocaine dependent subjects compared to non-drug using controls. There are several pathological mechanisms that could be responsible for these findings, since FA can be reduced through damage to axonal tracts and by neuronal loss. One way of obtaining more information about pathology underlying changes in FA on DTI is diffusion tensor eigenvalues, representing diffusion along the fiber tract (λ1) or perpendicular to the fiber tract (λT). Thirteen cocaine dependent subjects and 18 healthy controls underwent full brain DTI. Eigenvalues λ1 and λT of the corpus callosum were compared between cocaine users and controls. For λT there was a significant interaction of group × region of corpus callosum. Exploratory analysis of the subregions showed higher λT in the genu of the anterior corpus callosum of cocaine dependent subjects compared to control subjects. For λ1 there was no significant interaction of group × region of corpus callosum. Based on prior studies suggesting that alteration or damage to myelin increases diffusion perpendicular to the direction of fiber tracts (λT) with minimal effect on λ1 these findings are consistent with altered myelin in the corpus callosum in cocaine dependent subjects.