Downfield proton MRSI with whole-brain coverage at 3T

Area of Science:

• Magnetic Resonance Imaging
• Neuroimaging
• Metabolomics

Background:

• Magnetic Resonance Spectroscopic Imaging (MRSI) is crucial for non-invasively detecting and quantifying metabolites in the brain.
• Previous 2D downfield (DF) MRSI techniques offered limited coverage and resolution.
• Developing advanced MRSI protocols is essential for comprehensive brain metabolite analysis.

Purpose of the Study:

• To develop and validate a 3D downfield (DF) MRSI protocol for whole-brain coverage.
• To establish a post-processing pipeline for generating accurate metabolite maps.
• To assess the feasibility of high-resolution metabolite mapping in the human brain.

Main Methods:

• A 3D, circularly phase-encoded DF MRSI sequence was implemented and tested at 3T.
• Whole-brain metabolite maps with 0.7 cm³ nominal spatial resolution were acquired in healthy volunteers.
• A dedicated MRSI post-processing pipeline was developed for data analysis.

Main Results:

• LCModel analysis demonstrated low Cramer-Rao lower bounds (3-4%) for protein amide resonances, indicating good quantification accuracy.
• Significant regional differences in specific metabolite peaks were identified between brain regions (p < 0.020).
• DF concentration maps showed visual homogeneity across the brain, with reliable uncertainty estimates.

Conclusions:

• 3D DF MRSI is a feasible technique for whole-brain metabolite mapping at 3T.
• The protocol achieves a nominal spatial resolution of 0.7 cm³.
• This method allows for the mapping of exchangeable amide and other resonances across wide brain coverage.