Diffusion MRI is a new medical imaging modality of great interest in neuroimaging research. This modality enables the characterization in vivo of local micro-structures. Tensors have commonly been used to model the diffusivity profile at each voxel. This multivariate data set requires the design of new dedicated image processing techniques. The context of my thesis was the automatic analysis of intra-patient longitudinal changes with application to the follow-up of neuro-degenerative pathologies. New models and statistical tests for the automatic detection of changes in temporal sequences of diffusion images were developped. Tractography techniques that allows to probe brain connections in vivo were also used as priors.