title: A new approach to structural integrity assessment based on axial and radial diffusivities.
abstract: This study describes a method for performing diffusivity measures along and across a specific direction, derived from white matter in healthy controls. The diffusion tensor (DT) assigns a principal eigenvector (v₁) and eigenvalue (axial diffusivity, d(ax)) to each voxel. The average of the second and third eigenvalues is the radial diffusivity, d(rad) v₁ may be affected by pathology, therefore when comparing d(ax) and d(rad) in patients one has to consider the direction of the measurement and underlying anatomy. Here we created a representative super-DT dataset, DT(ref), whose eigenvector, v(1,ref), was considered the most likely direction of diffusivity per voxel. We defined the projected axial diffusivity, d(p-ax), as the projection of individual DTs along v(1,ref) and the projected radial diffusivity, d(p-rad), as the average of the projections along the second and third eigenvectors of DT(ref). The projected diffusivities are promising new parameters for studying white matter pathology.
authors.affiliation: NMR Research Unit, Queen Square MS Centre, Department of Neuroinflamtion, UCL Institute of Neurology, London, UK. c.wheeler-kingshott@ion.ucl.ac.uk
authors.forename: Claudia A M
authors.initials: CA
authors.lastname: Wheeler-Kingshott
authors.forename: Olga
authors.initials: O
authors.lastname: Ciccarelli
authors.forename: Torben
authors.initials: T
authors.lastname: Schneider
authors.forename: Daniel C
authors.initials: DC
authors.lastname: Alexander
authors.forename: Mara
authors.initials: M
authors.lastname: Cercignani
mesh_terms: D000328:Adult; D016880:Anisotropy; D001921:Brain / Q000502:physiology*; D056324:Diffusion Tensor Imaging; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009413:Nerve Fibers, Myelinated / Q000502:physiology*