DTI and Other Novel MRI Techniques: to better understand the role of microstructural damage and plasticity in multiple sclerosis
Diffusion magnetic resonance imaging (dMRI) is sensitive to brain microstructural changes and provides an indirect in vivo measure of the size and orientation of brain cells. This unique ability has been instrumental in studying the complexity of multiple sclerosis (MS) pathophysiology.
dMRI has been extensively applied to the study of patients with MS and has provided important insights in the development of clinical disability and progression of the disease. Diffusion tensor imaging (DTI) is the most commonly used dMRI technique and provides indices such as mean diffusivity which measures the magnitude of diffusion and fractional anisotropy which measure fiber directionality.
DTI has enabled a better understanding of how microscopic brain tissue damage contributes to clinical and cognitive disability. In addition, dMRI tractography has made possible the reconstruction of specific white matter tracts and the estimation of tract-specific metrics thus allowing the study of selective pathways associated with specific functional impairments. Furthermore, dMRI is the only technique able to map structural connectivity and obtain a “connectome” of the healthy and diseased brain and, therefore, can help understanding how brain connectivity and the corresponding behavioral correlates can be altered by MS.
Despite several advantages, DTI provides empirical diffusion measures that lack pathological specificity. The last decade has witnessed the development of a new set of techniques with a better specificity for the pathological changes associated to MS and other neurological diseases. Although more technically demanding these new methods have the potential to be used not only in research but also in clinical settings thank to the recent advancements in MRI software and hardware.
The main findings of DTI studies investigating lesional and normal-appearing brain tissue injury in MS will be presented. Novel dMRI techniques developed to increase pathological specificity and requiring either diverse tissue models and mathematical representation or specialized sequences will be reviewed. Studies exploring white matter plasticity by using dMRI before and after a physical or cognitive training will be discussed.