Atrophy and diffusion tensor MRI metrics of brain fiber bundles. Application to primary progressive multiple sclerosis patients

Recent applications of diffusion tensor (DT) magnetic resonance imaging (MRI) in primary progressive (PP) multiple sclerosis (MS) patients have contributed to the understanding of the nature of the damage in the grey and white matter (WM) of the brain (1). Nevertheless, correlations with clinical disability are weak. Regional studies have shown promising results, when DT-derived metrics were averaged over clinically eloquent sites (2,3). Also, brain atrophy is a well-known feature of MS which is viewed as a potential marker of irreversible tissue damage (4). In this study, we wished to examine whether the correlation of MRI measures with disability could improve when considering the tissue damage limited to the pyramidal tracts (PYT) and the corpus callosum (CC), instead of considering the whole brain. To this aim, an index of atrophy and DT derived metrics were obtained for the PYT and the CC.