Motion-Robust Direct Myelin Imaging in MRI using Self-Gating.

Direct myelin imaging with inversion-recovery ultrashort-echo-time (IR-UTE) is highly motion-sensitive, yet extra hardware or longer scans are impractical. We evaluated whether a superior-inferior (SI) self-navigator with bit-reversed spoke-angles mitigates motion artifacts without extending acquisition. Dual-echo IR-UTE was implemented at 3T. After an adiabatic inversion pulse, 21 spokes were acquired per segment around the white-matter null point, and dual-echo subtraction suppressed residual long-T2 signals. Adding SI-navigators at the end of each segment allows motion detection without lengthening TR. And bit-reversal is used to pseudo-randomize the spoke-angles. Bloch simulations of a 2D synthetic brain removed 10% of spokes to mimic gating. Three volunteers were scanned: (i) sequential-ordering, no-motion; (ii) bit-reversed, no-motion; (iii) bit-reversed with deliberate head nods. The navigator rejected 1,280 of 12,000 spokes (10.7%) during nodding, and the same gating was reconstructed on motion-free data. Simulation showed coherent streaks for sequential ordering but an isotropic point-spread function for bit-reversal. In vivo, gating degraded only the sequential dataset. bit-reversal preserved subcortical and deep-white-matter detail. During intentional nodding, gating with bit-reversal enhanced myelin contrast, outperforming the image reconstructed from the ungated data. The SI-navigator plus bit-reversal enables effective motion gating without hardware or time penalty, supporting routine motion-robust myelin mapping.