The impact of white matter microstructure with multi-fiber populations on gradient-echo frequency maps and QSM

A hollow cylinder fiber model (HCFM) with two orientation-dispersed fiber populations was used to characterize white matter microstructure-based susceptibility effects. The resulting TE-dependent frequency shifts were fitted with a curve function parameterized by a microstructure induced frequency difference (Δf) and bulk susceptibility induced frequency shift (Cf). Local frequency and QSM reconstruction using the fitted Cf versus using weighted echo averaging were compared by a head phantom and in vivo human brain data. Δf provided a useful contrast to illustrate the underlying white matter microstructure and Cf helped to improve the quantification accuracy of tissue magnetic susceptibility using QSM.