Exploiting gradient-echo frequency evolution: Probing white matter microstructure and extracting bulk susceptibility-induced frequency for quantitative susceptibility mapping

• Published in: Magnetic resonance in medicine Vol. 91; no. 4; pp. 1676 - 1693
• Main Authors: Chen, Lin, Shin, Hyeong-Geol, van Zijl, Peter C M, Li, Xu
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 01.04.2024
• Subjects: Cylinder heads; Evolution; Fibers; Frequency shift; In vivo methods and tests; Mapping; Mathematical models; Microstructure; Parameters; Populations; Reconstruction; Simulation; Substantia alba; Susceptibility; QSM; microstructure-induced frequency; TE-dependent frequency; gradient-echo frequency evolution; bulk susceptibility-induced frequency
• ISSN: 0740-3194; 1522-2594
• DOI: 10.1002/mrm.29958

This work is to investigate the microstructure-induced frequency shift in white matter (WM) with crossing fibers and to separate the microstructure-related frequency shift from the bulk susceptibility-induced frequency shift by model fitting the gradient-echo (GRE) frequency evolution for potentially more accurate quantitative susceptibility mapping (QSM). A hollow-cylinder fiber model (HCFM) with two fiber populations was developed to investigate GRE frequency evolutions in WM voxels with microstructural orientation dispersion. The simulated and experimentally measured TE-dependent local frequency shift was then fitted to a simplified frequency evolution model to obtain a microstructure-related frequency difference parameter ( ) and a TE-independent bulk susceptibility-induced frequency shift ( ). The obtained was then used for QSM reconstruction. Reconstruction performances were evaluated using a numerical head phantom and in vivo data and then compared to other multi-echo combination methods. GRE frequency evolutions and -based tissue parameters in both parallel and crossing fibers determined from our simulations were comparable to those observed in vivo. The TE-dependent frequency fitting method outperformed other multi-echo combination methods in estimating in simulations. The fitted , , and QSM could be improved further by navigator-based B fluctuation correction. A HCFM with two fiber populations can be used to characterize microstructure-induced frequency shifts in WM regions with crossing fibers. HCFM-based TE-dependent frequency fitting provides tissue contrast related to microstructure ( ) and in addition may help improve the quantification accuracy of and the corresponding QSM.