FIG. 10.

a: Directionally color-encoded fractional anisotropy (FA) maps before (i) and after (ii) correcting for subject motion and eddy current-induced geometric distortions. The bright rim (see enlarged region), clearly visible in (i), is practically nonexistent in the corrected image (ii). In this example, geometric distortions and subject motion in the DW images are corrected for simultaneously. As a result, the orientation of the diffusion gradients should be adjusted to take potential head rotations into account. In (b), the difference in orientation of the estimated first eigenvector between the uncorrected (i) and the corrected (ii) gradient directions is shown in a region of the genu. To fully appreciate the effect of neglecting this processing step, the glyph representations of the first eigenvectors are shown in (iii) (blue: uncorrected; yellow: corrected), focusing on the mid-sagittal region, which corresponds with the black rectangle in (i) and (ii). Although the errors shown in (iii) seem small and, therefore, perhaps deemed insignificant, the tractography results in (c) clearly show the deviation in the reconstructed fiber tract pathways when subject motion and eddy current-induced geometric distortions are not taken into account.