Figure 8.

Tract-based spatial statistics (TBSS) processing pipeline. (Left to right) DTI-derived fractional anisotropy (FA) images are co-registered to a template; they are then averaged, from which a “skeleton” containing all major tract centers common to all subjects is derived. Skeleton voxels with low FA-values (typically FA < 0.2) are excluded to ensure only white matter is present. Next, spatially normalized FA images are projected to the skeleton. In this step, the center of each tract is identified for each individual FA image, and projection vectors to their analogous location in the skeleton are computed and applied. Transformation fields (to template space) and projection vectors (to the skeleton) are then also applied to the additional DTI parametric maps (i.e., MD, λ₁, RD). Finally, non-parametric, permutation based, statistical testing of the null-hypothesis is performed.