Multi-gradient-echo myelin water fraction imaging: Comparison to the multi-echo-spin-echo technique.

Purpose: Myelin water fraction (MWF) mapping based on multi-gradient recalled-echo (MGRE) imaging has been proposed as an alternative to the conventional multi-echo-spin-echo (MESE) approach. In this work, we performed a comparative study of MESE and MGRE-derived MWFs in the same subject group.

Methods: MESE and MGRE data were acquired in 12 healthy volunteers at 3T. T2* decay curves were corrected for the effects of field inhomogeneities and multicomponent analysis of T2  and T2* signals was performed using non-negative least-squares fitting.

Results: When comparing MGRE and MESE-MWFs across volunteers, no significant differences were observed between average values in WM, deep GM (dGM), and cortical GM (cGM) that were (14 ± 3%), (6 ± 2%), and (8 ± 2%) for MGRE, and (13 ± 2%), (6 ± 1%), and (7 ± 1%), respectively, for MESE. The MGRE and MESE-MWFs showed a strong correlation (r  = 0.84) and Bland-Altman analysis revealed a small positive bias of (0.8 ± 1.6%) (absolute difference) for the MGRE-MWF.

Conclusion: Overall, we observed excellent agreement between the two techniques. The small positive bias of the MGRE-MWF is thought to be a consequence of its potentially reduced sensitivity to water exchange effects, compared to the MESE-MWF. This work suggests that with careful correction for the effects of field inhomogeneities, MGRE-MWF imaging is a promising alternative to the MESE approach. Magn Reson Med 79:1439-1446, 2018. © 2017 International Society for Magnetic Resonance in Medicine.