Matthew Cronin1, Samuel J. Wharton1, Richard W. Bowtell2
1Sir Peter Mansfield Magnetic Resonance Centre, The University of Nottingham, Nottingham, Notts, United Kingdom; 2Sir Peter Mansfield Magnetic Resonance Centre, University of Nottingham, Nottingham, Notts, United Kingdom
Although correct mathematical expressions for calculating field perturbations due to anisotropic magnetic susceptibility have been described, its effects have often been modelled using a simplified approach in which the anisotropy is represented by allocating the material an isotropic susceptibility whose magnitude depends on orientation to the field. Here we demonstrate using theory and experiment that this approximation leads to errors in predicting the frequency perturbation due to anisotropic structures. We also show that correct calculations predict interesting behaviour in a hollow cylinder model of the myelin sheath, and go on to demonstrate this behaviour experimentally in a simple model system.