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Abstract #1841

Reliable estimation of the MRI-visible effective axon radius using light microscopy: the need for large field-of-views

Laurin Mordhorst1, Maria Morozova2,3, Sebastian Papazoglou1, Björn Fricke1, Jan Malte Oeschger1, Henriette Rusch3, Carsten Jäger2, Markus Morawski2,3, Nikolaus Weiskopf2,4, and Siawoosh Mohammadi1,2
1Institute of Systems Neuroscience, University Medical Center Hamburg-Eppendorf, Hamburg, Germany, 2Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany, 3Paul Flechsig Institute of Brain Research, University of Leipzig, Leipzig, Germany, 4Felix Bloch Institute for Solid State Physics, Faculty of Physics and Earth Sciences, Leipzig, Germany

MRI-based models enable non-invasive characterization of brain microstructure, e.g. the effective axon radius ($$$r_{\text{eff}}$$$). Often, these models were validated by small-field-of-view microscopy (sFoVM) images (~10³ axons). As $$$r_{\text{eff}}$$$ is dominated by large, sparsely occurring axons, sFoVM-based estimations may miss large axons and underestimate $$$r_{\text{eff}}$$$. We employed an in-house developed pipeline to estimate $$$r_{\text{eff}}$$$ on large-scale light microscopy (lsLM) sections with similar spatial extent as the voxel sizes in human MRI systems. Taking lsLM as a baseline, we showed that sFoVM is an unsuitable reference for $$$r_{\text{eff}}$$$ and verified the potential of $$$r_{\text{eff}}$$$ to capture relevant spatial, anatomical variation.

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