FIG. 2.
Maps of averaged diffusion metrics of the 42 subjects in the MNI standard space. Diffusion tensor imaging (DTI) metrics include fractional anisotropy (FA), axial diffusivity (AD), radial diffusivity (RD), and mean diffusivity (MD). Neurite orientation dispersion and density imaging (NODDI) metrics include axonal density (Vic) and orientation dispersion (OD). The q-space imaging metric is the zero displacement probability (P0) describing the tissue restriction. The gray scale is 0 to 3*10–6 mm2/s for the diffusivities and is 0 to 1 for FA, Vic, OD, and P0. High intensity in the FA and OD maps indicates high tissue coherence and low dispersion and vice versa. AD and RD have high white matter contrast only in compact fiber tracts with known single-fiber bundles, such as the corpus callosum and the internal capsule. The P0 map shows higher intensity in more restricted areas (i.e., white matter), as expected. White matter also has a higher intensity than gray matter in the Vic map, indicating higher axonal density. MNI, Montreal Neurological Institute.