This study expands on the current literature by examining the quality of white matter fiber structure in relation to adolescent binge drinking in the context of marijuana use. We used diffusion tensor imaging (DTI) to evaluate microscopic white matter change in vivo by estimating the diffusion of water molecules in neural tissue. Brain regions that are rich in fiber tracts have greater restriction in the directionality of water molecule movement [51], so diffusion measurements visualize the white matter bundles and describe the microscopic architecture of white matter tissue [9,51]. DTI exams were performed on: (1) adolescents with no substance use history, (2) those with a history of binge drinking, and (3) those with a history of concomitant binge drinking and marijuana use. We compared between groups two common scalar diffusion measurements: fractional anisotropy (FA), which reflects the directionally-dependent movement of water molecules along fiber tracts, and mean diffusivity (MD), reflecting the degree of overall displacement of water molecules in localized tissue [51,75]. Based on literature examining combined effects of alcohol and cannabinoids on neural toxicity in the immature brain [40]
