Rosette Spectroscopic Imaging for Whole-Brain Slab Metabolite Mapping at 7T: Acceleration Potential and...

Area of Science:

• Neuroimaging
• Magnetic Resonance Spectroscopy
• Brain Metabolism

Background:

• Whole-brain 1H-MRSI is crucial for understanding brain function and disease.
• Ultrahigh field strengths (≥7T) improve signal-to-noise ratio (SNR) but present challenges like long acquisition times and signal contamination.
• Existing techniques require optimization for speed and accuracy.

Purpose of the Study:

• To develop and validate accelerated 2D and 3D 1H-MRSI sequences using rosette trajectories.
• To improve water and lipid signal suppression for cleaner metabolic maps.
• To assess the reproducibility and potential for further acceleration of the developed 1H-MRSI technique.

Main Methods:

• Developed 2D and 3D short TR/TE 1H-FID-MRSI sequences with rosette trajectories.
• Implemented an optimized FAST water suppression scheme (76ms) and L2 regularization for lipid removal.
• Acquired whole-brain metabolic maps in under 6 minutes with excellent reproducibility (CV < 6% for major metabolites).

Main Results:

• Achieved nominal spatial resolutions of 4.48x4.48 mm2 (2D) and 4.48x4.48x4.50 mm3 (3D).
• Demonstrated excellent intra-session reproducibility for NAA, Glu, tCho, tCr, and Gly+Ins.
• Retrospective compressed sensing showed SSIM > 0.85 at R=2, suggesting potential for ~2-minute acquisition times.

Conclusions:

• The developed 1H-MRSI sequences offer a significant improvement in speed and quality for neurochemical mapping.
• The technique shows high reproducibility and potential for substantial acceleration using compressed sensing.
• This advancement could enhance the clinical utility of 1H-MRSI in studying brain functions and diseases.