\bibitem{Lori03}        N.F.~Lori, T.E.~Conturo, D.~Le Bihan,
                        {\it Definition of Displacement Probability and Diffusion Time in q-Space Magnetic Resonance Measurements
                        That Use Finite-Duration Diffusion-Encoding Gradients},
                        JMR {\bf 165}, 185, 2003.