B₀-insensitive image navigators for prospective motion-corrected MRS with localized second-order shimming

Area of Science:

• Magnetic Resonance Spectroscopy (MRS)
• Neuroimaging
• Biomedical Engineering

Background:

• Localized shimming in single-voxel MRS can cause significant B0 inhomogeneity outside the region of interest.
• This inhomogeneity degrades motion navigator images, hindering prospective motion correction.
• Higher-order shims cannot be switched between whole-brain and localized adjustments, complicating motion correction strategies.

Purpose of the Study:

• To develop novel motion navigators that are insensitive to B0 inhomogeneity.
• To enable prospective motion correction in MRS even with localized higher-order shimming.
• To maintain high spectral quality by addressing motion artifacts.

Main Methods:

• Modified a fast, high-resolution motion navigator using spiral-in/out k-space trajectories.
• Split the readout into multiple shot interleaves to shorten echo time and reduce B0 inhomogeneity effects.
• Assessed motion correction performance in healthy subjects at 3T and 7T using a sLASER sequence.

Main Results:

• Acquired excellent quality whole-brain navigator images despite significant B0 inhomogeneity.
• Maintained short navigator durations (94-103 ms/slice) with multi-shot interleaves.
• Achieved comparable spectral quality (water linewidth, metabolite SNR) with and without motion using prospective correction.

Conclusions:

• Developed B0-insensitive motion navigators for prospective motion correction in MRS.
• Enabled MRS with localized first- and second-order shims for optimal spectral linewidth.
• Facilitated robust motion correction without compromising spectral data quality.