  Tractography is typically performed for each subject using the diffusion
tensor imaging (DTI) data in its native subject space rather than in some space
common to the entire study cohort. Despite performing tractography on a
population average in a normalized space, the latter is considered less
favorably at the \emph{individual} subject level because it requires spatial
transformations of DTI data that involve non-linear warping and reorientation
of the tensors. Although the commonly used reorientation strategies such as
finite strain and preservation of principle direction are expected to result in
adequate accuracy for voxel based analyses of DTI measures such as fractional
anisotropy (FA), mean diffusivity (MD), the reorientations are not always exact
except in the case of rigid transformations. Small imperfections in
reorientation at individual voxel level accumulate and could potentially affect
the tractography results adversely. This study aims to evaluate and compare
deterministic white matter fiber tracking in non-linearly warped DTI against
that in native DTI. The data present promising evidence that tractography in
non-linear warped DTI data could indeed be a viable and valid option for
various statistical analysis of DTI data in a spatially normalized space.
