FIG. 4.

A slice of a 6 h cell-treated animal longitudinally showing the sensitivity of fractional anisotropy (FA) and entropy to structural restoration. At 1 day after traumatic brain injury (TBI) (A–C), both FA (B) and entropy (C) detect the hypointensive area in the cortex region, which corresponds to the hyperintensive lesion identified on T2 (A). From 1 day to 2 weeks after TBI (D–F), entropy reveals the dramatic evolution of structural status (compare F with C), which nicely matches the apparent change of T2 lesion (compare D with A) in both size and shape, with restored tissue region captured on entropy (red arrow in F) corresponding to recovery area from hyperintensities on T2 (compare D with F). This structural restoration, however, is not reflected on FA (compare E with B). The tissue recovery area present on entropy (red arrow in F), but absent on FA, mainly contains crossing fibers, as shown by fiber orientation map (G).