A 31-channel integrated 'AC/DC' B(0) shim and RF receive array coil for improved 7 Tesla MRI

PURPOSE: To test an integrated “AC/DC” array approach at 7 Tesla, where B(0) inhomogeneity poses an obstacle for functional imaging, diffusion-weighted MRI, MR spectroscopy, and other applications. METHODS: A close-fitting 7T 31-channel brain array was constructed and tested using combined Rx and ΔB(0) shim channels driven by a set of rapidly-switchable current amplifiers. The coil was compared to a shape-matched 31-channel reference receive-only array for RF safety, signal-to-noise ratio (SNR), and inter-element noise correlation. We characterize the coil array’s ability to provide global and dynamic (slice-optimized) shimming using ΔB(0) field maps and echo planar imaging (EPI) acquisitions. RESULTS: The SNR and average noise correlation were equivalent to the 31ch reference array. Global and slice-optimized shimming provide 11% and 40% improvements respectively compared to baseline 2(nd)-order spherical harmonic shimming. Birdcage transmit coil efficiency was similar for the reference and AC/DC array setups. CONCLUSION: Adding ΔB(0) shim capability to a 31ch 7T receive array can significantly boost 7T brain B(0) homogeneity without sacrificing the array’s RF performance, potentially improving ultra-high field neuroimaging applications that are vulnerable to off-resonance effects.