David O. Brunner

Learn More
Multiple-channel RF transmission holds great promise for MRI, especially for human applications at high fields. For calibration it requires mapping the effective RF magnetic fields, B(1) (+), of the transmitter array. This is challenging to do accurately and fast due to the large dynamic range of B(1) (+) and tight SAR constraints. In the present work, this(More)
PURPOSE 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. THEORY AND METHODS Frequency-swept pulses as inputs are analyzed(More)
We introduce matched-filter fMRI, which improves BOLD (blood oxygen level dependent) sensitivity by variable-density image acquisition tailored to subsequent image smoothing. Image smoothing is an established post-processing technique used in the vast majority of fMRI studies. Here we show that the signal-to-noise ratio of the resulting smoothed data can be(More)
Parallel radio frequency transmission has recently been explored as a means of tailoring the spatial response of MR excitation. In particular, parallel transmission is increasingly used to accelerate radio frequency pulses that rely on time-varying gradient fields to achieve selectivity in multiple dimensions. The design of the underlying multiple-channel(More)
Reconstruction of MRI data is based on exact knowledge of all magnetic field dynamics, since the interplay of RF and gradient pulses generates the signal, defines the contrast and forms the basis of resolution in spatial and spectral dimensions. Deviations caused by various sources, such as system imperfections, delays, eddy currents, drifts or externally(More)
MRI relies on static and spatially varying dynamic magnetic fields of high accuracy. NMR field probes permit the direct observation of spatiotemporal field dynamics for diverse purposes such as data correction, field control, sequence validation, and hardware characterization. However, due to probe signal decay and dephasing existing field cameras are(More)
PURPOSE 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. METHODS To cover variation in physical constitution and(More)
PURPOSE 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. METHODS Magnetic field dynamics were monitored during the echo planar imaging readout of a common diffusion-weighted MRI sequence(More)
PURPOSE 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. THEORY AND(More)
  • 1