Imaging small vessel disease: lesion topography, networks, and cognitive deficits investigated with MRI.

Small vessel disease is a major contributor to the growing burden of cognitive impairment and dementia. In addition to diagnosis, MRI techniques provide a means to investigate mechanisms of cognitive decline. Studies that incorporate diffusion tensor MRI show that variance in cognitive performance is largely accounted for by alterations in brain structure. Unresolved questions about the link between structure and function include: (1) the relative importance of a small number of strategic lesions versus the cumulative effect of multiple lesions; (2) the underlying basis for the characteristic profile of cognitive impairment, with selective deficits of executive function, processing speed and working memory. This update focuses on MRI approaches to these problems and techniques to analyze spatial distribution of damage in relation to the networks that subserve major cognitive functions. Lesion mapping and voxel-based analysis, and the application of diffusion tensor MRI tractography to reconstruct critical white matter projections, are highly promising approaches for improving understanding of the relationship between structure and function and the mechanisms of cognitive decline.