Direct B 0 field monitoring and real‐time B 0 field updating in the human breast at 7 tesla

Large dynamic fluctuations of the static magnetic field ( B 0 ) are observed in the human body during MR scanning, compromising image quality and detection sensitivity in several MR imaging and spectroscopy sequences. Partially, these dynamic B 0 fluctuations are due to physiological motion such as breathing, but other sources of temporal B 0 field fluctuations are also present in the MR system (e.g., eddy currents). Especially at ultrahigh field (≥7 T), the increased susceptibility effects lead to large B 0 field variations over time. Direct measurement and correction of these temporal field variations of up to 70 Hz will lead to a significant reduction of artifacts and improved measurement stability/reproducibility. For direct measurement of the temporally changing B 0 field, a simple field probe was developed, that was placed in proximity to the tissue of interest. In this work, it is shown how such a field probe system can be used to monitor temporal B 0 field variations in the human body during MRI and magnetic resonance spectroscopy. Furthermore, it is shown how the acquired temporal B 0 field information can drive a dynamic shim module to directly correct the B 0 magnetic field in real time. Magn Reson Med, 2012. © 2011 Wiley Periodicals, Inc.