On the Nature of Phase Contrast in Gradient Echo MRI:A Generalized Lorentzian Approach

Xiang He¹, Dmitriy A. Yablonskiy^1,2

Herein we propose a theoretical framework based on the concept of Lorentzian ellipsoid that allows quantitative evaluation of brain tissue phase contrast in Gradient Echo MRI. Our approach takes into account the specific geometric properties of the magnetic susceptibility inclusions (mostly proteins, lipids, deoxyhemoglobin and non-heme iron) in the brain tissue. We demonstrated that not just the amount, but, more importantly, spatial distribution of the susceptibility inclusions at the sub-cellular level, as well as global cellular organization and its relative orientation with respect to the external B0 field are the dominant factors in the observed phase contrast.