Samuel James Wharton1, Richard Bowtell1
1Sir Peter Mansfield Magnetic Resonance Centre, School of Physics and Astronomy, University of Nottingham, Nottingham, United Kingdom
Recent work has demonstrated that the magnetic susceptibility of white matter has a measurable anisotropy. The likely source of this anisotropy is the myelin sheath that surrounds axons and specifically, the highly ordered aliphatic chains in the myelin. Here, we derive analytical expressions which characterise the field perturbation due to a model of the myelin sheath consisting of a hollow cylinder in which the magnetic susceptibility is anisotropic and the principal component of the susceptibility tensor is radially directed. The expressions are validated by imaging a cylindrical phantom incorporating a pyrolytic graphite sheet with a known, highly anisotropic, susceptibility.
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