The assessment of cerebral white matter microstructure in cerebral small vessel disease based on the diffusion-weighted magnetic resonance imaging

Introduction. Multidimensional or biophysical modelling approaches are actively used to examine the complex microstructure of brain matter in diffusion-weighted MRI, where tissue structures are schematically simplified and divided into separate regions to calculate the diffusion values. This approach demonstrates greater specificity when compared with the widely used diffusion tensor MRI (DT-MRI) and its metrics. The aim of the study was to compare DT-MRI and the biophysical diffusion models, and to evaluate their possible use in a more precise studying of the affected white matter in cerebral small vessel disease (CSVD). Materials and methods. We examined 96 patients (including 65 women; mean age 61.0±6.6 years) with CSVD and 23 healthy volunteers, comparable in age and gender (including 15 women; mean age 58±6 years). The patients were divided into 3 groups according to the severity of white matter disease as measured using the Fazekas scale. All study subjects underwent a brain MRI (3 T) with diffusion-weighted MRI (b = 0, 1000 and 2500 sec/mm 2 , 64 gradient directions) followed by the data processing; we obtained DT-MRI metric maps, as well as white matter tract integrity model and model using the spherical mean technique. Results. Significant differences were found between the study groups (except groups F0 and F1) in all metrics when the overall value of the white matter skeleton was examined ( p £ 0.05): there was a decrease in tissue anisotropy and axonal density in the white matter, as well as increased intra- and extra-axonal coefficients with more severe white matter disease. Analysis of individual white matter regions showed that the radial diffusion values had greater intergroup differences than the axial diffusion values in the corpus callosum (particularly, in the body and splenium). Conclusion. Biophysical models allow us to evaluate white matter disease in patients with CSVD using structural tissue features and indirect measures of intra- and extracellular diffusion. To clarify and increase the statistical significance of the obtained results, it is necessary to analyse the diffusion metrics using data from a larger patient sample.