2020/12/03 by Henrik Lundell, Chloé Najac, Lundell, Henrik +9
Medicine · #Advanced Neuroimaging Techniques and Applications #MRI in cancer diagnosis #Advanced MRI Techniques and Applications
paper · pdf · doi:10.48550/arxiv.2012.01796
Double diffusion encoding (DDE) magnetic resonance measurements of the water\nsignal offers a unique ability to separate the effect of microscopic\nanisotropic diffusion in structural units of tissue from the overall\nmacroscopic orientational distribution of cells. However, the specificity in\ndetected microscopic anisotropy is limited as the signal is averaged over\ndifferent cell types and across tissue compartments. Performing side-by-side\nmetabolite DDE spectroscopy (DDES) and water DDES in which a wide range of\nb-values is used to gradually eliminate the extracellular contribution provides\ncomplementary measures from which intracellular and extracellular microscopic\nfractional anisotropies (\μFA) and diffusivities can be estimated.\nMetabolites are largely confined to the intracellular space and therefore\nprovide a benchmark for intracellular diffusivity of specific cell types. Here,\nwe aimed to estimate tissue- and compartment-specific human brain\nmicrostructure by combining water and metabolites DDES experiments. We\nperformed DDES in human subjects in two brain regions that contain widely\ndifferent amounts of white matter (WM) and gray matter (GM): parietal white\nmatter (PWM) and occipital gray matter (OGM) on a 7 T MRI scanner. Results of\nthe metabolite DDES experiments in both PWM and OGM suggest a highly\nanisotropic intracellular space within neurons and glia, with the possible\nexception of gray matter glia. Tortuosity values in the cytoplasm for water and\ntNAA, obtained with correlation analysis of microscopic parallel diffusivity\nwith respect to GM/WM tissue fraction in the volume of interest, are remarkably\nsimilar for both molecules, while exhibiting a clear difference between gray\nand white matter, suggesting a more crowded cytoplasm and more complex\ncytomorphology of neuronal cell bodies and dendrites in GM than those found in\nlong-range axons in WM.\n