On the performance of multi-compartment relaxometry for myelin water imaging (MCR-MWI) – test-retest repeatability and inter-protocol reproducibility

• Published in: NeuroImage (Orlando, Fla.) Vol. 266; p. 119824
• Main Authors: Chan, Kwok-Shing, Chamberland, Maxime, Marques, José P.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.02.2023; Elsevier Limited; Elsevier
• Subjects: Bias; Brain - diagnostic imaging; Brain mapping; Diffusion weighted imaging; Experiments; Gradient echo imaging; Humans; Image processing; Longitudinal studies; Magnetic Resonance Imaging - methods; Microstructure; Myelin; Myelin Sheath - metabolism; Myelin water imaging; Neuroimaging; Reproducibility; Reproducibility of Results; Substantia alba; Water - analysis; TE1; Gradient echo imaging; MCR-MWI; MCR-DIMWI; ΔTE; MW; IQR; TA; Myelin water imaging; VFA; TE; EW; CV; HCM; IEW; Microstructure; IE; Diffusion weighted imaging; TR
• ISSN: 1053-8119; 1095-9572; 1095-9572
• DOI: 10.1016/j.neuroimage.2022.119824

•Multi-compartment relaxometry for myelin water imaging (MCR-MWI) can be performed with data comprising as few as 3 flip angles without introducing substantial bias or instability in the fitting procedure.•MCR-MWI is a reproducible measure of myelin water fraction (MWF) and incorporating DWI can further improve the measurement reproducibility.•MCR-MWI allows the acquisition of whole-brain 1.5 mm isotropic MWF maps in 9 min, even without the use of advanced model-based reconstructions.•Small MWF bias can present in cross-protocol comparison if the MT effect is not constant across GRE protocols (e.g., different TRs or flip angle combinations).•Compartmental relaxation parameters derived from MCR-MWI possess complimentary information beyond myelin water concentration. In this study, we optimized the variable flip angle (VFA) acquisition scheme using numerical simulations to shorten the acquisition time of multicompartment relaxometry for myelin water imaging (MCR-MWI) to a clinically practical range in the absence of advanced image reconstruction methods. As the primary objective of this study, the test-retest repeatability of myelin water fraction (MWF) measurements of MCR-MWI is evaluated on three gradient echo (GRE) sequence settings using the optimized VFA schemes with different echo times and repetition times, emulating various scanner setups. The cross-protocol reproducibility of MCR-MWI and MCR with diffusion-informed myelin water imaging (MCR-DIMWI) is also examined. As a secondary objective, we explore the bundle-specific profiles of various microstructural parameters from MCR-(DI)MWI and their cross-correlations to determine if these parameters possess supplementary microstructure information beyond myelin concentration. Numerical simulations indicate that MCR-MWI can be performed with a minimum of three flip angles covering a wide range of T1 weightings without adding significant bias. This is supported by the results of an in vivo experiment, allowing whole-brain 1.5 mm isotropic MWF maps to be acquired in 9 min, reducing the total scan time to 40% of the original implementation without significant quality degradation. Good test-retest repeatability is observed for MCR-MWI for all three GRE protocols. While good correlations can also be found in MWF across protocols, systematic differences are observed. Bundle-specific MWF analysis reveals that certain white matter bundles are similar in all participants. We also found that microstructure relaxation parameters have low linear correlations with MWF. MCR-MWI is a reproducible measure of myelin. However, attention should be paid to the protocol related MWF differences when comparing different studies, as the MWF bias up to 0.5% can be observed across the protocols examined in this work.