Whole brain multiparametric mapping in two minutes using a dual-flip-angle stack-of-stars blipped multi-gradient-echo...

A new MRI technique is presented for three-dimensional fast simultaneous whole brain mapping of myelin water fraction (MWF), T₁, proton density (PD), R₂*, magnetic susceptibility (QSM), and B₁ transmit field (B₁⁺). Phantom and human (N = 9) datasets were acquired using a dual-flip-angle blipped multi-gradient-echo (DFA-mGRE) sequence with a stack-of-stars (SOS) trajectory. Images were reconstructed using a subspace-based algorithm with a locally low-rank constraint. A novel joint-sparsity-constrained multicomponent T₂*-T₁ spectrum estimation (JMSE) algorithm is proposed to correct for the T₁ saturation effect and B₁⁺/B₁^- inhomogeneities in the quantification of MWF. A tissue-prior-based B₁⁺ estimation algorithm was adapted for B₁ correction in the mapping of T₁ and PD. In the phantom study, measurements obtained at an acceleration factor (R) of 12 using prospectively under-sampled SOS showed good consistency (R² > 0.997) with Cartesian reference for R₂*/T_1app/M_0app. In the in vivo study, results of retrospectively under-sampled SOS with R = 6, 12, 18, showed good quality (structure similarity index measure > 0.95) compared with those of fully-sampled SOS. Besides, results of prospectively under-sampled SOS with R = 12 showed good consistency (intraclass correlation coefficient > 0.91) with Cartesian reference for T₁/PD/B₁⁺/MWF/QSM/R₂*, and good reproducibility (coefficient of variation < 7.0 %) in the test-retest analysis for T₁/PD/B₁⁺/MWF/R₂*. This study has demonstrated the feasibility of simultaneous whole brain multiparametric mapping with a two-minute scan using the DFA-mGRE SOS sequence, which may overcome a major obstacle for neurological applications of multiparametric MRI.