On the Role of Neuronal Magnetic Susceptibility and Structure Symmetry on Gradient Echo MR Signal Formation

Alexander L. Sukstanskii¹, Dmitriy A. Yablonskiy¹

In this communication we analyze the effect of magnetic anisotropy associated with the presence of radially-oriented long-chain lipoprotein molecules in the myelin sheath of WM fibers on gradient echo MRI signal formation. We incorporate this effect into previously developed Generalized Lorentzian approach and calculate water frequency shifts in axons, myelin and extracellular space. Frequency shifts in axons and myelin sheath are shown to be highly anisotropic with respect to B₀. Importantly, both the cylindrical symmetry of WM tissue structure and of magnetic susceptibility contribute to this anisotropic effect. It is also shown that myelin water signal is substantially non-T2* type.