Axonal loss in multiple sclerosis lesions: magnetic resonance imaging insights into substrates of disability. - van Waesberghe,J.H.; Kamphorst,W.; De Groot,C.J.; van Walderveen,M.A.; Castelijns,J.A.; Ravid,R.; Lycklama,A.; Nijeholt,G.J.; van der Valk,P.; Polman,C.H.; Thompson,A.J.; Barkhos,F. (Ann Neurol, 1999)