A probabilistic white matter atlas approach to assessing age related changes in the brain

Introduction: Spatial normalisation of diffusion data allows diffusion properties to be compared across a population without any bias from macrostructural differences in tissue anatomy. Standard approaches perform spatial normalisation of diffusion tensors. However streamline tractography through lattices of tensors is mainly suited to reconstruction of major white matter fibres. In contrast probabilistic approaches allow tractography through areas of fibre crossing and low anisotropy. This study constructs a probabilistic white matter atlas by combining posterior distributions on the principal direction of diffusion (PDD) at each voxel for multiple subjects. Tracts are then propagated through the atlas using probabilistic tractography. These therefore represent a consensus for the population. We compare fractional anisotropy (FA) at all voxels along tracts between the insula and lingual gyrus across two populations: 20-30, and 60-90 years. This demonstrates age related changes in FA between frontal and posterior regions of the brain.