10.5 T In Vivo Head Imaging With Universal RF Shimming

TL;DR

This paper introduces a universal RF shim for 10.5T MRI that eliminates the need for time-consuming subject-specific calibration, improving brain imaging efficiency.

Contribution

A universal B1+ shim for 10.5T MRI that reduces calibration time while maintaining image quality.

Findings

The universal B1+ shim showed no significant differences in whole-brain tissue segmentation compared to subject-specific methods.

Minor variations were observed in subcortical regions but did not affect overall reliability.

The universal shim reduces examination time by eliminating separate data acquisition and optimization.

Abstract

Brain MR imaging at 10.5 T ultra‐high field offers significant improvements in signal‐to‐noise ratio (SNR), but faces challenges with B1
+ inhomogeneity. Parallel‐transmission (pTx) can be used to achieve a more uniform RF field distribution, but necessitates the use of B1
+ calibration in the region of interest. This study explores a universal B1
+ shim solution on 10.5 T that could eliminate the need for time‐consuming subject‐specific B1
+ calibration.

B1
+ data from 7 participants (19 sessions) were used to develop the universal B1
+ shim, which was then validated against traditional subject‐specific approaches using T1‐weighted MP2RAGE structural images in 5 participants (6 sessions). Statistical comparisons of tissue and subcortical segmentations were conducted using popular neuroimaging tools SPM and FreeSurfer, respectively.

The universal shim rapidly converged with a small training dataset, likely due to consistent positioning and the simplicity of B1
+ shimming used for head imaging. Whole‐brain tissue segmentation showed no statistically significant differences between universal and subject‐specific solutions, with only minor variations near the ventricles and inferior brain regions in the detailed subcortical segmentation. The proposed universal B1
+ shim reduces examination time by removing the need for separate data acquisition and optimization.

These findings suggest that the universal B1
+ shim is a viable substitute for subject‐specific approaches, offering a more efficient solution for neuroimaging applications. Additionally, it confirms that 10.5 T MRI can produce reliable structural brain imaging data, paving the way for broader adoption of ultra‐high field MRI in neuroimaging research.

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