Direct B0 field monitoring and real-time B0 field updating in the human breast at 7 tesla

Abstract

Large dynamic fluctuations of the static magnetic field (B0) 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 B0 fluctuations are due to physiological motion such as breathing, but other sources of temporal B0 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 B0 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 B0 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 B0 field variations in the human body during MRI and magnetic resonance spectroscopy. Furthermore, it is shown how the acquired temporal B0 field information can drive a dynamic shim module to directly correct the B0 magnetic field in real time. Magn Reson Med, 2012. © 2011 Wiley Periodicals, Inc.