Samuel James Wharton1, Richard Bowtell1
1Sir Peter Mansfield Magnetic Resonance Centre, School of Physics and Astronomy, University of Nottingham, Nottingham, United Kingdom
Recent studies at high magnetic field strengths have shown that there is a direct link between the orientation of white matter fibers to the main magnetic field and the contrast observed in magnitude and phase images acquired using gradient echo MRI. Understanding the origin of this link could offer researchers access to a new diagnostic tool for investigating tissue microstructure. Here, we show that fibre-orientation-dependent contrast in magnitude and phase images can be fully explained by modelling nerve fibers as long, hollow cylinders of myelin, within which: (i) myelin-water generates a rapidly-decaying signal and (ii) the magnetic susceptibility is anisotropic.