Magnetic Susceptiblity Induced MR Signal Frequency Shift in White Matter - Experimental Comparison Between Lorentzian Sphere and Generalized Lorentzian Approaches

Jie Luo¹, Xiang He², Dmitriy A. Yablonskiy³, ⁴

Phase images obtained by gradient echo MRI provide enhanced contrast of the brain anatomy. Possible origins of the phase/frequency contrast such as the magnetic susceptibility and the water-macromolecule exchange effects have been discussed. To describe the influence of tissue magnetic susceptibility on MR signal frequency shift, a proper relationship between these two values should be established. In this study, we have demonstrated that the Generalized Lorentzian Approach provides satisfactory explanation of the angular dependence of the phase contrast in longitudinal structures such as axons in white matter while usually assumed Lorentzian Sphere Approximation fails.