Abstract #0712

The impact of axon orientation dispersion and 3D diameter variations on the transverse apparent diffusion coefficient

Mariam Andersson^1,2, Jonathan Rafael-Patino³, Hans Martin Kjer^1,2, Vedrana Andersen Dahl¹, Alexandra Pacureanu⁴, Martin Bech⁵, Anders Bjorholm Dahl¹, Jean-Philippe Thiran^3,6, and Tim B. Dyrby^1,2

¹Department of Applied Mathematics and Computer Science, Technical University of Denmark, Kgs. Lyngby, Denmark, ²Danish Research Centre for Magnetic Resonance, Hvidovre, Denmark, ³Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland, ⁴The European Synchrotron, Grenoble, France, ⁵Department of Medical Radiation Physics, Clinical Science, Lund University, Lund, Sweden, ⁶Radiology Department, Centre Hospitalier Universitaire Vaudois and University of Lausanne, Lausanne, Switzerland

We extract the orientation dispersion (OD) and 3D axon diameter variations of long axons (>100 µm) from an ultra-high resolution, synchrotron X-ray nano-holotomography (XNH) scan of the monkey splenium. From this, we discover a relationship between mean axon diameter and along-axon diameter variations. Monte Carlo simulations are then performed on the intra-axonal spaces (IAS) of different substrates which inherit their morphological features from the segmented axons. These simulations show that the OD significantly affects the transverse apparent diffusion coefficient (ADC_⟂) of the axon substrate at diffusion times up to 50 ms, while diameter variations do not.

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