Samuel James Wharton1, Richard Bowtell1
1Sir Peter Mansfield Magnetic Resonance Centre, School of Physics and Astronomy, University of Nottingham, Nottingham, United Kingdom
There is an ongoing debate about the source of the small difference in the frequency of signals from cortical grey matter (GM) and adjacent white matter (WM) that is manifested in phase images of the human brain. Recently, it was shown that the evolution of the phase with TE in WM is non-linear. Here, we assess the contribution of this non-linear phase evolution to the average GM/WM frequency difference at 7 T. The results show that non-linear phase effects may be the dominant source of the GM/WM frequency difference seen in phase images acquired using long echo times (> 17ms).