FIG 2. Region of interest placement for selection of individual portions of the fornix.

The fornix was selected in 3 distinct portions, because this enhances the selection accuracy. For each portion, tract-selection regions were manually drawn on either FA or principal diffusivity color maps. To be selected, the tracts had to go through the middle tract-selection region (B, F, and J, green boxes) and through either one of the extreme regions (A or C; E or G; I or K, for the crus, body, and columns, respectively). The FA maps presented are derived from CSF-suppressed DTI. The same procedure was repeated for the standard DTI datasets by using identical tract selection regions. The resulting FLAIR DTI-derived tracts of a healthy subject are presented in 3D views overlaid on anatomic 3D-MPRAGE axial and sagittal sections (D, H, and L). Subsequent analyses of all segments were performed only between the 2 extreme tract selection regions. A, anterior; P, posterior; ac, anterior commissure; fc, fusion of the crura; sCCi, inferior border of the splenium of the corpus callosum. Panel E is 0.5 cm posterior to the vertical AC line. Panel K is parallel to the inferior border of the body of the fornix.