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

Area of Science:

• Neuroimaging
• Magnetic Resonance Imaging (MRI)

Background:

• Direct myelin imaging using inversion-recovery ultrashort-echo-time (IR-UTE) is crucial for neurological assessments.
• However, IR-UTE is highly sensitive to motion artifacts, limiting its clinical applicability.
• Existing solutions for motion correction often require additional hardware or prolonged scan durations, which are impractical.

Purpose of the Study:

• To evaluate a novel motion mitigation strategy for IR-UTE myelin imaging.
• To assess the efficacy of a superior-inferior (SI) self-navigator combined with bit-reversed spoke angles.
• To determine if this approach can reduce motion artifacts without extending acquisition time.

Main Methods:

• Implementation of dual-echo IR-UTE sequence at 3T with an adiabatic inversion pulse.
• Acquisition of 21 spokes per segment around the white-matter null point, followed by dual-echo subtraction.
• Integration of SI self-navigators and bit-reversal for motion detection and spoke angle pseudo-randomization.
• Bloch simulations and in vivo scans on three volunteers under varying motion conditions.

Main Results:

• The SI self-navigator with bit-reversal successfully detected and rejected motion, rejecting 10.7% of spokes during nodding.
• Simulations indicated that bit-reversal yields an isotropic point-spread function, unlike sequential ordering.
• In vivo scans demonstrated that the proposed method preserved white-matter detail and enhanced myelin contrast during motion.

Conclusions:

• The SI self-navigator combined with bit-reversal provides effective motion gating for IR-UTE myelin imaging.
• This technique significantly reduces motion artifacts without necessitating extra hardware or longer scan times.
• It supports the routine implementation of motion-robust myelin mapping in clinical settings.