Correction of main and transmit magnetic field (B0 and B 1) inhomogeneity effects in multicomponent-driven equilibrium single-pulse observation of T1 and T2

摘要

Multicomponent-driven equilibrium single-component observation of T 1 and T2 offers a new approach to multiple component relaxation time and myelin water analysis. The method derives two-component relaxation information from spoiled and fully balanced steady-state (SPGR and bSSFP) imaging data acquired over multiple flip angles. Although these steady-state imaging techniques afford rapid acquisition times and high signal-to-noise ratio efficiency, they are also sensitive to main (B 0) and transmit (B1) magnetic field inhomogeneities. These effects alter the measured signal from their theoretical values and lead to substantive errors in the derived myelin volume fraction estimates. Here, we incorporate correction techniques to mitigate these effects. DESPOT1-HIFI is used to first calibrate the transmitted flip angles; and B0 affects are removed through the inclusion of an additional parameter in the multicomponent-driven equilibrium single-component observation of T1 and T2 fitting, coupled with the acquisition of multiple phase-cycled bSSFP data. The performance of these correction techniques was evaluated using numerical simulations, demonstrating effective removal of B0 and B1-induced errors in the derived myelin fraction relaxation parameters. The approach was also successfully demonstrated in vivo, with near artifact-free whole-brain, high spatial resolution (1.7 mm × 1.7 mm × 1.7 mm isotropic voxels) myelin water fraction maps acquired in a clinically feasible 16 min.