Diffusion Tensor Imaging – A special type of diffusion weighted imaging (DWI) that is used to image white matter tracts (nerve axon tracts) within the central nervous system.  White matter tracts’ axons have physical properties that are anisotropic (directionally dependent) and this causes variation in the rate of water molecule migration in a magnetic field depending on direction.  DTI measures this variability to generate images or maps of white fiber tract orientation within the CNS.