Improving brain B(0) shimming using an easy and accessible multi-coil shim array at ultra-high field

OBJECT: Improve shimming capabilities of ultra-high field systems, with addition of an accessible low-complexity B(0) shim array for head MRI at 7 T. MATERIALS AND METHODS: An eight channel B(0) shim coil array was designed as a tradeoff between shimming improvement and construction complexity, to provide an easy to use shim array that can be employed with the standard 7 T head coil. The array was interfaced using an open-source eight-channel shim amplifier rack. Improvements in field homogeneity for whole-brain and slice-based shimming were compared to standard second-order shimming, and to more complex higher order dynamic shimming and shim arrays with 32 and 48 channels. RESULTS: The eight-channel shim array provided 12% improvement in whole brain static shimming and provided 33% improvement when using slice-based shimming. With this, the eight-channel array performed similar to third-order dynamic shimming (without the need for higher order eddy current compensation). More complex shim arrays with 32 and 48 channels performed better, but require a dedicated RF coil. DISCUSSION: The designed eight-channel shim array provides a low-complexity and low-cost approach for improving B(0) field shimming on an ultra-high field system. In both static and dynamic shimming, it provides improved B(0) homogeneity over standard shimming.