Dixon-based B0 self-navigation in radial stack-of-stars multi-echo gradient echo imaging

Purpose: To develop a Dixon-based B-0 self-navigation approach to estimate and correct temporal B0 variations in radial stack-of-stars gradient echo imaging for quantitative body MRI. Methods: The proposed method estimates temporal B-0 variations using a B-0 self-navigator estimated by a graph-cut-based water-fat separation algorithm on the oversampled k-space center. The B-0 self-navigator was employed to correct for phase differences between radial spokes (one-dimensional [1D] correction) and to perform a motion-resolved reconstruction to correct spatiotemporal pseudo-periodic B-0 variations (three-dimensional [3D] correction). Numerical simulations, phantom experiments and in vivo neck scans were performed to evaluate the effects of temporal B-0 variations on the field-map, proton density fat fraction (PDFF) and T-2(& lowast;) map, and to validate the proposed method. Results: Temporal B-0 variations were found to cause signal loss and phase shifts on the multi-echo images that lead to an underestimation of T-2(& lowast;), while PDFF mapping was less affected. The B-0 self-navigator captured slowly varying temporal B-0 drifts and temporal variations caused by respiratory motion. While the 1D correction effectively corrected B-0 drifts in phantom studies, it was insufficient in vivo due to 3D spatially varying temporal B-0 variations with amplitudes of up to 25 Hz at 3 T near the lungs. The proposed 3D correction locally improved the correction of field-map and T-2(& lowast;) and reduced image artifacts. Conclusion: Temporal B-0 variations particularly affect T-2(& lowast;) mapping in radial stack-of-stars imaging. The self-navigation approach can be applied without modifying the MR acquisition to correct for B-0 drift and physiological motion-induced B-0 variations, especially in the presence of fat.