Abstract #1501

Mapping the myelin g-ratio: promises and pitfalls

Jennifer SW Campbell¹, Ilana R Leppert¹, Mathieu Boudreau¹, Sridar Narayanan¹, Julien Cohen-Adad^2,3, G B Pike^1,4, and Nikola Stikov^2,5

¹Montreal Neurological Institute, Montreal, QC, Canada, ²Ecole Polytechnique, University of Montreal, Montreal, QC, Canada, ³Functional Neuroimaging Unit, University of Montreal, Montreal, QC, Canada, ⁴Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada, ⁵Montreal Heart Institute, Montreal, QC, Canada

The aggregate myelin g-ratio is a function of the myelin volume fraction (MVF) and the fiber volume fraction (FVF). While this relationship holds in theory, obtaining precise and accurate MRI measures of the MVF and FVF remains a challenge. Most MVF mapping techniques have been linearly correlated with histology, but the literature suggests that the slope and intercept are acquisition dependent. In this work, we focus on three magnetization transfer (MT) derived MVF metrics (MTR, MT_sat and qMT) and explore how improper calibration of the MVF estimates propagates to the aggregate g-ratio. The result of an incorrect MVF calibration is not simply loss in sensitivity to g-ratio changes, but rather g-ratio trends that are statistically significant, incorrect, and highly dependent on the fiber volume fraction changes.

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