Data Stitching for Dynamic Field Monitoring With NMR Probes

To propose a new method for characterizing sequences with higher resolution or readout length than allowed by standard field monitoring approaches.

Our proposed method was devised to characterize entire readout gradients by stitching multiple segment-specific dynamic field measurements obtained across a matched number of consecutive TRs corresponding to a certain segmentation of the readout gradient. The utility of our proposed stitching method for high-order dynamic field measurements was illustrated using 2D spiral sequences. It was first demonstrated at 10.5 T and then at 7 T using both simulated and experimental MRI data. At 10.5 T, two extreme spiral readout scenarios were considered where standard field monitoring did not work. Our method was then validated in humans at 7 T, where spiral sequences were employed for brain imaging. At 7 T, our method was further compared against gradient impulse response function (GIRF)-based trajectory prediction.

At 10.5 T, our stitching method outperformed the standard approach, producing plausible dynamic field measurements throughout entire readouts. At 7 T, it produced nearly identical measurements for one readout where standard field monitoring also worked; for another readout when standard field monitoring did not work, it still produced sensible field measurements, improving image reconstruction for both simulated and experimental MRI data.

Our proposed stitching method provides an effective means to characterize challenging imaging gradients using commercially available hardware and without assuming a linear gradient system, thereby having utility for many applications especially those aiming for ultrahigh-resolution MRI at ultrahigh field.