Optimising diffusion measurements for large-scale, multicentre multiple sclerosis trials: a pan-European study - Perego, E; Rovaris, M; Hirsch, J; Pagani, E; Gass, A; Pouwels, P; Rosendaal, S; Barkhof, F; Agosta, F; Caputo, D; Giorgio, A; Palace, J; et al. (2008)