Abstract #4483

G-ratio Calculation in Multiple Sclerosis: The Impact of Diffusion Modelling for Axonal and Fiber Volume Fraction Determination

Tigris Joseph^1,2, Shannon H. Kolind^1,2,3,4, Guojun Zhao³, Peng Sun⁵, Robert Carruthers³, Alice Schabas³, Ana-Luiza Sayao³, Virginia Devonshire³, Roger Tam^4,6, G. R. Wayne Moore^2,3,7, David K. B. Li^3,4, Sheng-Kwei Song⁸, Anthony Traboulsee³, Irene M. Vavasour^2,4, and Cornelia Laule^1,2,4,7

¹Physics and Astronomy, University of British Columbia, Vancouver, BC, Canada, ²International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, BC, Canada, ³Medicine, University of British Columbia, Vancouver, BC, Canada, ⁴Radiology, University of British Columbia, Vancouver, BC, Canada, ⁵Imaging Physics, MD Anderson Cancer Center, Houston, TX, United States, ⁶School of Biomedical Engineering, University of British Columbia, Vancouver, BC, Canada, ⁷Pathology & Laboratory Medicine, University of British Columbia, Vancouver, BC, Canada, ⁸Radiology, Washington University, St. Louis, MO, United States

Synopsis

Keywords: Multiple Sclerosis, White Matter, myelin, axons, g-ratio, brain, microstructure, lesions, normal appearing white matter, multiple sclerosis

G-ratio is the ratio of the inner axonal diameter to the total outer diameter, including myelin. MRI-derived g-ratios in multiple sclerosis (MS) may convey microstructural tissue abnormalities. G-ratios were estimated using myelin water fraction scaled to myelin volume fraction, and axonal metrics from Diffusion Basis Spectrum Imaging (DBSI), Neurite Orientation Dispersion and Density Imaging (NODDI), Spherical Mean Technique (SMT), and ActiveAx for axon/fiber volume fraction in 122 MS patients. DBSI and ActiveAx derived g-ratios were higher in lesions than normal appearing white matter (NAWM), reflecting MS pathology. NODDI and SMT derived g-ratios were unexpectedly lower in lesions than NAWM.

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