Diffusion MRI-based cortical complexity alterations associated with executive function in multiple sclerosis

Purpose: To report a novel magnetic resonance imaging measure (diffusion orientational complexity [DOC]) in a study of people with multiple sclerosis (MS) and healthy controls and to determine patterns of abnormality, correlations with conventional diffusion measures, and associations with cognitive function.

Materials and methods: We performed high angular resolution diffusion imaging (HARDI) and measured DOC, mean diffusivity (MD), and fractional anisotropy (FA) in 51 MS patients and 28 healthy controls. All subjects had a 2-mm isotropic HARDI scan on a 3 T scanner using a 32-channel head receiver coil. DOC, MD, and FA were measured in three regions of interest (ROIs) in frontal cortex linked to executive function, two ROIs in occipital cortex thought unlikely to affect cognition, and in the whole cortex.

Results: Frontal cortex DOC was significantly decreased in MS patients. DOC correlated mostly with FA but not MD in controls and with MD but not FA in people with MS. In regression models that included all three diffusion-based measures, frontal cortex DOC and frontal cortex FA independently predicted executive function scores.

Conclusion: DOC is a new useful measure of functionally relevant cortical pathology in MS, providing information that complements conventional diffusion measures.