Intra-voxel and inter-voxel coherence in patients with multiple sclerosis assessed using diffusion tensor MRI

Previous diffusion tensor magnetic resonance imaging (DT-MRI) studies reported mean diffusivity ((D) over bar) and fractional anisotropy (FA) changes in lesions and normal-appearing white matter (NAWM) of patients with multiple sclerosis (MS), but neglected the additional information which can be obtained by the analysis of the inter-voxel coherence (Q. The present study is based on a large sample of patients with MS and it is aimed at assessing the potential role of C in the quantification of MS-related tissue damage of T2-visible lesions and NAWM. We obtained dual-echo, T1-weighted and DT-MRI scans from 78 patients with relapsing-remitting (RR), secondary progressive (SP), or primary progressive (PP) MS and from 26 healthy volunteers. We calculated (D) over bar FA and C of T2-hyperintense lesions, T1-isointense lesions, T1-hypointense lesions and several areas of the NAWM. (D) over bar and FA of the majority of NAWM regions studied from MS patients were different from the corresponding quantities of the white matter from controls. NAWM C from patients was lower than white matter C from controls only for the parietal pericallosal areas. SPMS patients had higher corpus callosum (D) over bar and lower corpus callosum FA and C than patients with either RRMS or PPMS. Average lesion (D) over bar was higher, and average FA and C lower than the corresponding quantities measured in the NAWM. Average T1-hypointense lesion (D) over bar was higher and average FA lower than the corresponding quantities of T1-isointense lesions, whereas average C of these two lesion populations were not different. SPMS had higher average lesion (D) over bar than both PPMS and RRMS patients. NAWM (D) over bar and C of the corpus callosum were moderately correlated with disability. This study confirms the role of DT-MRI metrics to identify MS lesions with different amounts of tissue damage and to detect diffuse changes in the NAWM. It also shows that measuring C enables us to obtain additional information about tissue damage, which is complementary to that given by the analysis of (D) over bar and FA.