Iulius Dragonu1, Nicoleta Baxan1, 2, Markus Wick2, Jeff Snyder3, Franek Hennel2, Jrgen Hennig1, Dominik von Elverfeldt1, Maxim Zaitsev1
1Dept. Radiology - Medical Physics, University Medical Center Freiburg, Freiburg, Germany; 2Bruker BioSpin MRI GmbH, Ettlingen, Germany; 3Dept. of Neurology, University Medical Center Freiburg, Freiburg, Germany
Discontinuities in the magnetic susceptibility generate induction fields which perturb the static B0 field. At high B0 fields the susceptibility difference effects are enhanced leading to potential shimming problems. The problem of finding the correct shim values can become ill-conditioned for very thin or off-centred volumes. In such cases, the required linear independence of shim functions is not maintained leading to shim degeneracy. In this work, we propose a new method for solving the shim degeneracy problem in order to calculate the correct shim values. In addition, this technique will optimize the shim currents taking into account the limitations of the maximum current available for each shim channel.