Benjamin E. Dietrich

ZTE imaging in humans.

Zero echo time (ZTE) imaging is a robust and silent 3D radial technique suitable for direct MRI of tissues with very rapid transverse relaxation. Given its successful application on micro‐ and animal MRI systems, the purpose of this work is to enable and demonstrate ZTE imaging in humans using a whole‐body magnet.

Real-time feedback for spatiotemporal field stabilization in MR systems

MR imaging and spectroscopy require a highly stable, uniform background field. The field stability is typically limited by hardware imperfections, external perturbations, or field fluctuations of physiological origin. The purpose of the present work is to address these issues by introducing spatiotemporal field stabilization based on real‐time sensing and feedback control.

Retrospective correction of physiological field fluctuations in high‐field brain MRI using concurrent field monitoring

Magnetic field fluctuations caused by subject motion, such as breathing or limb motion, can degrade image quality in brain MRI, especially at high field strengths. The purpose of this study was to investigate the feasibility of retrospectively correcting for such physiological field perturbations based on concurrent field monitoring.

A field camera for MR sequence monitoring and system analysis

MR image formation and interpretation relies on highly accurate dynamic magnetic fields of high fidelity. A range of mechanisms still limit magnetic field fidelity, including magnet drifts, eddy currents, and finite linearity and stability of power amplifiers used to drive gradient and shim coils. Addressing remaining errors by means of hardware, sequence, or signal processing optimizations, calls for immediate observation by magnetic field monitoring. The present work presents a stand‐alone monitoring system delivering insight into such field imperfections for MR sequence and system analysis.

Field camera measurements of gradient and shim impulse responses using frequency sweeps

Applications of dynamic shimming require high field fidelity, and characterizing the shim field dynamics is therefore necessary. Modeling the system as linear and time‐invariant, the purpose of this work was to measure the impulse response function with optimal sensitivity.

Real-time motion correction using gradient tones and head-mounted NMR field probes.

Sinusoidal gradient oscillations in the kilohertz range are proposed for position tracking of NMR probes and prospective motion correction for arbitrary imaging sequences without any alteration of sequence timing. The method is combined with concurrent field monitoring to robustly perform image reconstruction in the presence of potential dynamic field deviations.

Feedback field control improves linewidths in in vivo magnetic resonance spectroscopy.

Magnetic resonance spectroscopy (MRS) experiments rely on a homogeneous and stable magnetic field within the sample. Field homogeneity is typically optimized by static B0 shimming while reproducible effects from dynamic field variation are commonly diminished by means of gradient system calibration as well as calibration based on non‐water suppressed reference data. However, residual encoding deficiencies from incomplete calibration and nonreproducible field perturbations deteriorate the quality of the obtained data. To overcome this problem, we propose to adapt higher‐order feedback field control based on NMR field probes for its application in MRS.

Monitoring, analysis, and correction of magnetic field fluctuations in echo planar imaging time series.

To assess the utility of concurrent magnetic field monitoring for observing and correcting for variations in k‐space trajectories and global background fields that occur in single‐shot echo planar imaging (EPI) time series as typically used in functional MRI (fMRI).

Diffusion MRI with concurrent magnetic field monitoring

Diffusion MRI is compromised by unknown field perturbation during image encoding. The purpose of this study was to address this problem using the recently described approach of concurrent magnetic field monitoring.

Utility of real‐time field control in T2*‐Weighted head MRI at 7T

Real‐time field control can serve to reduce respiratory field perturbations during T2* imaging at high fields. This work investigates the effectiveness of this approach in relation to key variables such as patient physique, breathing patterns, slice location, and the choice of sequence.