2H transmit–receive NMR probes for magnetic field monitoring in MRI



Measuring image encoding fields in real time and applying the information in postprocessing offer improved image quality for MRI, particularly for applications that are intrinsically sensitive to gradient imperfections. For this task, a stand-alone magnetometer system based on multiple 2H transmit–receive NMR probes has been developed. The conceptual advantages of changing to 2H NMR probes for 1H magnetic field monitoring are elucidated here, and the practical design of the probes is described. In comparison to previous 1H NMR probe-based designs, 2H probes are perfectly decoupled from standard 1H imaging. Utilization of RF shielding or other nonoptimal decoupling schemes is therefore not needed. Probes based on 2H nuclei are also more easily miniaturized for high-resolution imaging. This is particularly important for diffusion tensor and phase-contrast imaging, which rely on strong motion-sensitizing gradients. The presented 2H NMR probes have been shown to fulfill the requirements for accurate 1H imaging down to image resolutions of 0.2 mm. Using susceptibility matching techniques, the probe's B0 inhomogeneity-induced signal dephasing is reduced and monitoring periods beyond 200 msec are achieved. The benefit of real time magnetic field monitoring is highlighted for phase-contrast and non-Cartesian multishot imaging. Magn Reson Med, 2011. © 2010 Wiley-Liss, Inc.