Mesoscale Whole-Brain T₂*-Weighted and Associated Quantitative MRI in Humans at 10.5 T

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Neuroimaging
• Biophysics

Background:

• Ultra-high field (UHF) MRI, particularly beyond 7 Tesla (T), offers enhanced signal-to-noise ratio and contrast.
• T2*-weighted (T2*w) imaging is sensitive to magnetic field variations, providing insights into tissue microstructure and composition.
• Quantitative mapping of R2* relaxation rate and magnetic susceptibility (χ) can offer more robust biomarkers than qualitative imaging.

Purpose of the Study:

• To demonstrate mesoscale whole-brain T2*-weighted MRI at 10.5 T.
• To quantify R2* relaxation rate and magnetic susceptibility (χ) at 10.5 T.
• To evaluate the T2*w contrast at 10.5 T compared to 7 T.

Main Methods:

• Multi-echo gradient recalled echo (ME-GRE) data acquired at 0.5 mm isotropic resolution in healthy adults at 10.5 T.
• Navigator-guided joint motion and field correction for whole-brain image reconstruction.
• Quantitative R2* and χ mapping, with analysis in volumetric and surface-based regions of interest (ROIs).
• Comparison with data acquired at 7 T using a similar protocol.

Main Results:

• High-quality whole-brain T2*w images were obtained at 10.5 T, allowing detailed R2* and χ mapping.
• A linear relationship (slope 1.52) was observed between R2* values at 10.5 T and 7 T, consistent with known field dependencies.
• Magnetic susceptibility (χ) was largely field-independent, except in the basal ganglia where it was lower at 10.5 T.
• Normalized R2* contrast increased by ~3% between brain regions and 12% between cortical depths from 7 T to 10.5 T.

Conclusions:

• High-quality mesoscale whole-brain T2*w MRI and quantitative R2* and χ mapping are feasible at 10.5 T.
• The findings support the potential for optimizing anatomic T2*w brain MRI at ultrahigh fields (>7 T).
• This technique may enhance visualization of fine-scale brain structures and improve diagnostic capabilities.