title: In vivo histology of the myelin g-ratio with magnetic resonance imaging.
abstract: The myelin g-ratio, defined as the ratio between the inner and the outer diameter of the myelin sheath, is a fundamental property of white matter that can be computed from a simple formula relating the myelin volume fraction to the fiber volume fraction or the axon volume fraction. In this paper, a unique combination of magnetization transfer, diffusion imaging and histology is presented, providing a novel method for in vivo magnetic resonance imaging of the axon volume fraction and the myelin g-ratio. Our method was demonstrated in the corpus callosum of one cynomolgus macaque, and applied to obtain full-brain g-ratio maps in one healthy human subject and one multiple sclerosis patient. In the macaque, the g-ratio was relatively constant across the corpus callosum, as measured by both MRI and electron microscopy. In the human subjects, the g-ratio in multiple sclerosis lesions was higher than in normal appearing white matter, which was in turn higher than in healthy white matter. Measuring the g-ratio brings us one step closer to fully characterizing white matter non-invasively, making it possible to perform in vivo histology of the human brain during development, aging, disease and treatment.
authors.affiliation: Montreal Neurological Institute, McGill University, Montreal, Canada; École Polytechnique de Montréal, Montreal, Canada. Electronic address: nikola.stikov@polymtl.ca.
authors.forename: Nikola
authors.initials: N
authors.lastname: Stikov
authors.affiliation: Montreal Neurological Institute, McGill University, Montreal, Canada.
authors.forename: Jennifer S W
authors.initials: JS
authors.lastname: Campbell
authors.affiliation: Montreal Neurological Institute, McGill University, Montreal, Canada.
authors.forename: Thomas
authors.initials: T
authors.lastname: Stroh
authors.affiliation: Montreal Neurological Institute, McGill University, Montreal, Canada.
authors.forename: Mariette
authors.initials: M
authors.lastname: Lavelée
authors.affiliation: Montreal Neurological Institute, McGill University, Montreal, Canada.
authors.forename: Stephen
authors.initials: S
authors.lastname: Frey
authors.affiliation: Montreal Neurological Institute, McGill University, Montreal, Canada.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Novek
authors.affiliation: Montreal Neurological Institute, McGill University, Montreal, Canada.
authors.forename: Stephen
authors.initials: S
authors.lastname: Nuara
authors.affiliation: Montreal Neurological Institute, McGill University, Montreal, Canada.
authors.forename: Ming-Kai
authors.initials: MK
authors.lastname: Ho
authors.affiliation: Montreal Neurological Institute, McGill University, Montreal, Canada.
authors.forename: Barry J
authors.initials: BJ
authors.lastname: Bedell
authors.affiliation: Stanford University, Stanford, CA, United States.
authors.forename: Robert F
authors.initials: RF
authors.lastname: Dougherty
authors.affiliation: Montreal Neurological Institute, McGill University, Montreal, Canada.
authors.forename: Ilana R
authors.initials: IR
authors.lastname: Leppert
authors.affiliation: Montreal Neurological Institute, McGill University, Montreal, Canada.
authors.forename: Mathieu
authors.initials: M
authors.lastname: Boudreau
authors.affiliation: Montreal Neurological Institute, McGill University, Montreal, Canada.
authors.forename: Sridar
authors.initials: S
authors.lastname: Narayanan
authors.affiliation: École Polytechnique de Montréal, Montreal, Canada.
authors.forename: Tanguy
authors.initials: T
authors.lastname: Duval
authors.affiliation: École Polytechnique de Montréal, Montreal, Canada.
authors.forename: Julien
authors.initials: J
authors.lastname: Cohen-Adad
authors.affiliation: École supérieure d'ingénieurs en génie électrique, Rouen, France.
authors.forename: Paul-Alexandre
authors.initials: PA
authors.lastname: Picard
authors.affiliation: Université Laval, Quebec City, Canada.
authors.forename: Alicja
authors.initials: A
authors.lastname: Gasecka
authors.affiliation: Université Laval, Quebec City, Canada.
authors.forename: Daniel
authors.initials: D
authors.lastname: Côté
authors.affiliation: Montreal Neurological Institute, McGill University, Montreal, Canada; Hotchkiss Brain Institute and Department of Radiology, University of Calgary, Calgary, Alberta, Canada.
authors.forename: G Bruce
authors.initials: GB
authors.lastname: Pike
mesh_terms: D000328:Adult; D000818:Animals; D001369:Axons / Q000648:ultrastructure*; D001921:Brain / Q000648:ultrastructure*; D003337:Corpus Callosum / Q000648:ultrastructure; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D006801:Humans; D008252:Macaca fascicularis; D060328:Magnetic Phenomena; D008297:Male; D008818:Mice, Neurologic Mutants; D009103:Multiple Sclerosis / Q000473:pathology; D009186:Myelin Sheath / Q000648:ultrastructure*
keywords: Diffusion; Histology; Magnetization transfer; Myelin g-ratio; Quantitative MRI; White matter microstructure