title: A novel measure of fractional anisotropy based on the tensor distribution function.
abstract: Fractional anisotropy (FA), a very widely used measure of fiber integrity based on diffusion tensor imaging (DTI), is a problematic concept as it is influenced by several quantities including the number of dominant fiber directions within each voxel, each fiber's anisotropy, and partial volume effects from neighboring gray matter. With High-angular resolution diffusion imaging (HARDI) and the tensor distribution function (TDF), one can reconstruct multiple underlying fibers per voxel and their individual anisotropy measures by representing the diffusion profile as a probabilistic mixture of tensors. We found that FA, when compared with TDF-derived anisotropy measures, correlates poorly with individual fiber anisotropy, and may sub-optimally detect disease processes that affect myelination. By contrast, mean diffusivity (MD) as defined in standard DTI appears to be more accurate. Overall, we argue that novel measures derived from the TDF approach may yield more sensitive and accurate information than DTI-derived measures.
authors.affiliation: Laboratory of Neuroimaging, Dept. of Neurology, University of California, Los Angeles, USA.
authors.forename: Liang
authors.initials: L
authors.lastname: Zhan
authors.forename: Alex D
authors.initials: AD
authors.lastname: Leow
authors.forename: Siwei
authors.initials: S
authors.lastname: Zhu
authors.forename: Marina
authors.initials: M
authors.lastname: Baryshev
authors.forename: Arthur W
authors.initials: AW
authors.lastname: Toga
authors.forename: Katie L
authors.initials: KL
authors.lastname: McMahon
authors.forename: Greig I
authors.initials: GI
authors.lastname: de Zubicaray
authors.forename: Margaret J
authors.initials: MJ
authors.lastname: Wright
authors.forename: Paul M
authors.initials: PM
authors.lastname: Thompson
mesh_terms: D000465:Algorithms; D016880:Anisotropy; D001921:Brain / Q000166:cytology*; D056324:Diffusion Tensor Imaging / Q000379:methods*; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D009413:Nerve Fibers, Myelinated / Q000648:ultrastructure*; D010363:Pattern Recognition, Automated / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity