High resolution free-breathing respiratory-resolved volumetric lung imaging at 0.55T using stack-of-spiral out-in bSSFP

Motivation: High resolution free-breathing structural lung imaging at 0.55T has been demonstrated using bSSFP half-radial dual-echo imaging with constrained reconstruction within ~10-min scan time. Goal(s): To develop faster high-resolution free-breathing lung imaging using spiral sampling. Approach: We employ a stack-of-spirals out-in trajectory with constrained reconstruction along with pilot-tone based respiratory navigation. Results: Structural lung imaging is demonstrated with 2mm isotropic resolution, 5-7 respiratory states, and 5-7 min scan time. 3D ventilation maps are demonstrated, showing -3.1% ~ 70.2% lung capacity during normal and deep breathing. Impact: Free-breathing SoSOi can provide simultaneous structural and functional lung imaging at 0.55T within a 5-min scan, with improved sampling efficiency and lower undersampling factor compared to bSTAR. This has implications for the evaluation of lung function and chronic lung diseases.