Fig. 2.

Fractional anisotropy (FA) of corpus callosum. (A) FA map of a representative coronal slice of a rat brain diffusion tensor image with corresponding region of interest (red outline) in which voxels with FA >0.5 (green outline) defined the measureable corpus callosum. (B) Plot of mean corpus callosum FA values relative to baseline (defined as FA_t/FA₀) for 0 Gy (circles), 27 Gy (squares), and 34 Gy (triangles). FA significantly increased from baseline for all groups (effect of group: F_6,89 = 5.300, P=.0001). All animals had an increase in FA between baseline and 3 mo, indicating continued myelination, shown by plots >1 (relative to baseline: 0 Gy, P = .001; 27 Gy, P = .0001; and 34 Gy, P = .001). The 6-mo FA remained equivalent to 3-mo values for rats receiving 0 Gy of whole-brain irradiation (WBI), as well as rats receiving 27 Gy of WBI, but declined after 34-Gy WBI (0 Gy vs 34 Gy at 6 mo: P= .01). *P<.05. (A color version of this figure is available at www.redjournal.org.)