Increased Neurite Orientation-Dispersion and Density in the TgCRND8 Mouse Model of Amyloidosis: Inverse Relation with Functional Connectome Clustering and Modulation by Interleukin-6

Luis M. Colon-Perez; Kristen R. Ibanez; Mallory Suarez; Kristin Torroella; Kelly Acuna; Edward Ofori; Yona Levites; David E. Vaillancourt; Todd E. Golde; Paramita Chakrabarty; Marcelo Febo

The fitting of the intracellular volume fraction (i.e., zero-radius cylinders or 'sticks') involves the use of a Bingham-Watson series used in statistical shape analysis (Maier-Hein et al., 2015) and the results of the fitting process provides an index of the degree of orientation dispersion of socalled 'neurites'. For the parameter fitting procedure, we assumed a value of in vivo intrinsic diffusivity of 1.7 µm 2 /ms and isotropic diffusivity of 3.0 µm 2 /ms (Grussu et al., 2017) . The whole brain model-fitting generates maps of neurite density (NDI: relative concentration of zero-radius cylinders), orientation dispersion (ODI: 0 for no dispersion as in highly organized parallel fiber bundles to a maximum of 1 for the highest degree of dispersion, as in cerebral cortical grey matter), and the isotropic free water fraction (ISO: 0 low isotropy to a maximum isotropy of 1) (Grussu et al., 2017) .