Scientists are developing new tools to understand multiple sclerosis pathogenesis and monitor the benefits of treatments. One of these tools is diffusion tensor imaging (DTI), a novel technique that describes the microstructural organization of white matter tracts in the brain. Although DTI has greater pathological specificity than magnetic resonance imaging (MRI), certain aspects of the technique are still in progress.
“Decoding Diffusivity in Multiple Sclerosis: Analysis of Optic Radiation Lesional and Non-Lesional White Matter,” published in PLoS One, looked at pathological diffusivity changes in the brain by compartmentalizing tissue structures. Substrates within the brain are sometimes restricted from moving through the brain by membranes wrapped around neuronal axons and myelin sheaths. Since myelin is degrading in patients with multiple sclerosis, techniques that measure radial diffusivity should be useful to measure myelin degeneration. However, this is not the case, and a team from Macquarie University in Sydney, Australia wanted to investigate ways to improve the DTI technique.
Rather than use the common method of mathematical eigenvectors to describe tissue structures, the team of researchers, led by Dr. Alexander Klistorner and Dr. Michael H. Barnett, segmented (compartmentalized) the brain by seemingly similar pathological processes. They then used optic radiation on 50 relapsing-remitting multiple sclerosis patients.
When the authors conducted an asymmetry analysis of lesional and non-lesional neural fibers, they found an increase in radial diffusivity that correlated to lesional myelin loss. Looking at axial diffusivity, the researchers observed a relative increase in the distal part of lesional fibers. Finally, proximal diffusivity of transected axons appeared normal.
An increase in radial diffusivity was strongly correlated with global lesions, potentially the result of demyelination. The researchers noted that this demyelination was not detectable via conventional MRIs, demonstrating the superiority of DTI.
“This study highlights the utility of the compartmentalization approach in elucidating the pathological substrates of diffusivity and demonstrates the presence of tissue-specific patterns of altered diffusivity in MS, providing further evidence that DTI is a sensitive marker of tissue damage in both lesions and normal appearing white matter,” wrote Dr. Klistorner. “Our results suggest that, at least within the optic radiation, parallel and perpendicular diffusivities are affected by tissue restructuring related to distinct pathological processes.”