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

To demonstrate mesoscale whole-brain T₂*-weighted (T₂*w) MRI at 10.5 T, quantify R₂* relaxation rate and magnetic susceptibility (χ), and evaluate T₂*w contrast at such high field strength.

Multi-echo GRE (ME-GRE) data were collected in healthy adults at 0.5 mm isotropic resolution at 10.5 T. Whole-brain images were reconstructed with navigator-guided joint motion and field correction and were used for quantitative R₂* and χ mapping. Regional R₂* and χ values and R₂* contrast were analyzed in volumetric regions of interest (ROIs) and intra-cortical surface-based ROIs. For comparison, ME-GRE data from the same subjects were acquired using a similar protocol at 7 T.

High-quality whole-brain T₂*w images were obtained, enabling R₂* and χ mapping with delineation of fine-scale brain structures. Regional R₂* analysis revealed a linear relationship between 10.5 T and 7 T R₂* values with a slope of 1.52, in agreement with previously reported linear field dependency of R₂*. Estimated χ values were field-independent in most brain regions under consideration except for the basal ganglia where χ was observed to be lower at 10.5 T than at 7 T. The normalized R₂* contrast that is, the R₂* difference normalized by the mean R₂*, increased by about 3% between brain regions and 12% between cortical depths from 7 to 10.5 T.

It is feasible to achieve high-quality mesoscale whole-brain T₂*w MRI at 10.5 T and associated quantitative R₂* and χ mapping. Our results may aid future optimization of anatomic T₂*w brain MRI at ultrahigh field beyond 7 T.