A Simple Approach of Combined Passive and Active Shimming for In Vivo MR Spectroscopy at High Magnetic Field

High magnetic fields increase the sensitivity and spectral dispersion in MR spectroscopy. However, spectral peaks are broadened in vivo at higher field strength due to stronger susceptibility-induced effects. Strategies to minimize the spectral linewidth by optimal shimming are therefore of critical importance. In our current 7T MR system, the shim requirements exceeded the dynamic range of the second order active shim capabilities up to 10 times, which was overcome by a combined passive and active shim approach. Thereby, simple ferro-shim geometries were theoretically derived and applied for shimming of regions in the visual cortex of the macaque monkey.