The Orthogonal Shim Coil for 3T Brain Imaging

We designed and implemented an orthogonal shim array consisting of shim coils with their planes perpendicular to the planes of neighboring RF coils. This shim coil improves the magnetic field homogeneity by minimizing the interference to RF coils.

A, Converting “32‐channel orient 1” array to “39‐channel orthogonal” array by adding “7‐channel orthogonal” array, which was placed around the forehead as the brim of a baseball cap. B, “7‐channel orthogonal“ array. C, SNR maps at 3 representative slices of the “32‐channel orient 1“ array (top) and “39‐channel orthogonal” array (bottom).

A, Converting “32‐channel orient 1” array to “39‐channel orthogonal” array by adding “7‐channel orthogonal” array, which was placed around the forehead as the brim of a baseball cap. B, “7‐channel orthogonal“ array. C, SNR maps at 3 representative slices of the “32‐channel orient 1“ array (top) and “39‐channel orthogonal” array (bottom).

We developed a 7‐channel orthogonal shim array, whose coil plan was perpendicular to neighboring RF coils, at the forehead. A programmable open‐source current driver supplied shim currents. The 7‐channel orthogonal shim array caused only marginal SNR loss to the integrated 32‐channel RF‐shim array. The 7‐channel orthogonal shim array itself improved the magnetic field homogeneity by 30% in slice‐optimized shimming, comparable to the baseline shimming offered by the scanner’s 2nd order spherical harmonic shimming.

Zhou J, Stockmann JP, Arango N, Witzel T, Scheffler K, Wald LL, Lin FH.

An orthogonal shim coil for 3T brain imaging.

Magn Reson Med. 2020 Apr;83(4):1499-1511.