Rolf Pohmann

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PURPOSE Relaxation times, transmit homogeneity, signal-to-noise ratio (SNR) and parallel imaging g-factor were determined in the human brain at 3T, 7T, and 9.4T, using standard, tight-fitting coil arrays. METHODS The same human subjects were scanned at all three field strengths, using identical sequence parameters and similar 31- or 32-channel receive(More)
The optimization of k-space sampling for nonlinear sparse MRI reconstruction is phrased as a Bayesian experimental design problem. Bayesian inference is approximated by a novel relaxation to standard signal processing primitives, resulting in an efficient optimization algorithm for Cartesian and spiral trajectories. On clinical resolution brain image data(More)
Fourier imaging modalities suffer from significant signal contamination between adjacent voxels, especially when the spatial resolution is comparable to the size of the anatomical structures. This contamination can be positive or negative, depending on the spatial response function and the geometry of the object. Such a situation arises in human cardiac(More)
With the increasing use of ultrahigh-field MR with multiple transmit channels, mapping of the B₁(+) field has become a critical factor in many studies, leading to the publication of a large number of sequences for the measurement of the flip angle in recent years. In this article, the accuracy, precision and practicability of some of the most prominent of(More)
One of the main goals of ultra-high field MRI is to increase the spatial resolution reached in structural and functional images. Here, the possibility to obtain in vivo images of the human brain with voxel volumes below 0.02mm(3) is shown at 9.4T. To optimize SNR and suppress ringing artifacts, an acquisition-weighted 3D gradient-echo sequence is used,(More)
PURPOSE Subject motion can severely degrade MR images. A retrospective motion correction algorithm, Gradient-based motion correction, which significantly reduces ghosting and blurring artifacts due to subject motion was proposed. The technique uses the raw data of standard imaging sequences; no sequence modifications or additional equipment such as tracking(More)
Magnetic resonance imaging (MRI) is a noninvasive imaging technique that today constitutes one of the main pillars of preclinical and clinical imaging. MRI’s capacity to depict soft tissue in whole specimens ex vivo as well as in vivo, achievable voxel resolutions well below (100 μm)3, and the absence of ionizing radiation have resulted in the broad(More)
PURPOSE To develop and test a novel method for coil placement in interleaved transcranial magnetic stimulation (TMS)/functional MRI (fMRI) studies. MATERIALS AND METHODS Initially, a desired TMS coil position at the subject's head is recorded using a neuronavigation system. Subsequently, a custom-made holding device is used for coil placement inside the(More)
PURPOSE The increased signal-to-noise ratio and blood oxygen level dependent signal at ultra-high field can only help to boost the resolution in functional MRI studies if the spatial specificity of the activation signal is improved. At a field strength of 9.4 T, both gradient-echo and spin-echo based echo-planar imaging were implemented and applied to(More)
OBJECTIVES The aims of this study were to investigate the subjective discomfort and sensory side effects during ultrahigh field (UHF) magnetic resonance imaging (MRI) examinations in a large-scale study and to evaluate differences between magnetic resonance (MR) sites. MATERIALS AND METHODS Four MR sites with a 7-T MR system and 2 MR sites with a 9.4-T MR(More)