Universal B0 shimming for whole-brain MRI at 7T

Motivation: B0 shimming is essential for reducing field inhomogeneities in 7T brain MRI. However, the process is time-consuming and prone to inaccuracies due to large initial inhomogeneities or data processing errors. Goal(s): To propose a universal B0 shim which provides an improved initial guess for iterative shimming algorithms, a time-efficient option for fast acquisitions, and a backup option. Approach: A universal shim was calculated as the median of subject-specific shim coefficients. Shim performance was validated using B0 and EPI data. Results: Compared to default settings, the universal B0 shim reduces average B0 inhomogeneity by 78Hz, only 3Hz less than subject-specific shims. Impact: We propose an easy-to-use universal B0 shim for 7T brain MRI with similar performance to subject-specific shims. This can provide an improved initial estimate for iterative shimming, a time-efficient solution for ultrafast protocols, or a backup when subject-specific shimming fails.