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In vivo histology of the myelin g-ratio with magnetic resonance imaging.

Publication Type:

Journal Article

Source:

Neuroimage, Volume 118, p.397-405 (2015)

Keywords:

Adult, Animals, Axons, Brain, Corpus Callosum, Diffusion Magnetic Resonance Imaging, Humans, Macaca fascicularis, Magnetic Phenomena, Male, Mice, Neurologic Mutants, Multiple Sclerosis, Myelin Sheath

Abstract:

<p>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.</p>

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