Abstract #1128

The apparent orientation dependence of MTR, ihMTR and MWF is affected by local microstructural properties in white matter

Sarah Rosemary Morris^1,2,3, Irene M. Vavasour^3,4, Anastasia Smolina^5,6, Erin MacMillan^4,7, Guillaume Gilbert⁷, Michelle Lam^1,4, Piotr Kozlowski^1,2,3,4, Carl A. Michal¹, Alan Manning¹, Alex L. MacKay^1,3,4, and Cornelia Laule^1,2,3,4,8

¹Physics & Astronomy, University of British Columbia, Vancouver, BC, Canada, ²International Collaboration on Repair Discoveries, Vancouver, BC, Canada, ³Radiology, University of British Columbia, Vancouver, BC, Canada, ⁴UBC MRI Research Centre, Vancouver, BC, Canada, ⁵Medical Biophysics, University of Toronto, Toronto, ON, Canada, ⁶The Hospital for Sick Children, Toronto, ON, Canada, ⁷MR Clinical Science, Philips Healthcare Canada, Markham, ON, Canada, ⁸Pathology & Laboratory Medicine, University of British Columbia, Vancouver, BC, Canada

Synopsis

Keywords: White Matter, CEST & MT, inhomogeneous Magnetization Transfer, ihMT, myelin water fraction, MWF, magnetization transfer, MT, fibre direction, orientation dependence, diffusion tensor imaging (DTI), myelinWe measured MTR, ihMTR, MWF and fibre orientation from DTI in 17 white matter regions in 17 healthy adults at 3 T. All three metrics showed an apparent orientation dependence: MWF and ihMTR were lower in fibres perpendicular to B₀ by 6% and 1% respectively compared to those parallel, while MTR was lower by 0.5% at ~40°, with the highest values in fibres perpendicular to B₀. However, separating the apparent orientation dependence by region revealed large variation in the trends, suggesting that real differences in myelination and other microstructural properties are confounding the apparent orientation dependence measured using this method.

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