Claudia A.M. Wheeler-Kingshott1, Daniel C. Alexander2, Mara Cercignani3
1Department of Neuroinflammation, UCL Institute of Neurology, London, UK; 2Dept. Computer Science, University College London, Centre for Medical Image Computing, London, UK; 3Neuroimaging Laboratory , Fondazione Santa Lucia, Rome, Italy
Axial and radial diffusivities reflect the diffusion coefficient along and across white matter fibres and are potential biomarkers of axonal integrity and myelination. The principal eigenvalue of the diffusion tensor (DT) has been associated with axial diffusivity and the average of the second and third eigenvalues with radial diffusivity. Here we challenge this assumption, underlying the importance of analysing the DT eigenvalues together with their eigenvectors. We present simulations to illustrate the effect of pathology and compare the DT eigenvalues in two healthy controls and two patients with MS, using non-linear registration and the preservation of principal direction algorithm.