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Voss B.,University of Osnabruck | Nordmann J.,University of Osnabruck | Uhl A.,Biomedizinische Nmr Forschungs Gmbh Am Max Planck Institute For Biophysikalische Chemie | Komban R.,University of Osnabruck | Haase M.,University of Osnabruck
Nanoscale | Year: 2013

The origin of the narrow particle size distributions obtained in the oleic acid-based synthesis of hexagonal phase β-NaREF4 nanocrystals (RE = Sm, Eu, Gd, Tb) has been investigated. Compared to the standard synthesis, the growth conditions were simplified by using small purified particles of either α-NaREF4 (cubic phase) or β-NaREF4 (hexagonal phase) as single-source precursors, thereby avoiding the complications arising from the simultaneous presence of molecular educts and intermediately formed small particles. The study shows that α-phase as well as β-phase particles grow by Ostwald-ripening but narrow particle size distributions of the β-NaREF4 product particles are only obtained when α-phase precursor particles are employed. Since the small particles are also formed as intermediate products in the standard synthesis of β-NaSmF4, β-NaEuF4, β-NaGdF4 and β-NaTbF4 particles, their crystal phase is an important parameter to obtain a narrow size distribution in these systems. This journal is © The Royal Society of Chemistry. Source


Klosowski J.,Biomedizinische Nmr Forschungs Gmbh Am Max Planck Institute For Biophysikalische Chemie | Frahm J.,Biomedizinische Nmr Forschungs Gmbh Am Max Planck Institute For Biophysikalische Chemie
Magnetic Resonance in Medicine | Year: 2016

Purpose: To develop an image noise filter suitable for MRI in real time (acquisition and display), which preserves small isolated details and efficiently removes background noise without introducing blur, smearing, or patch artifacts. Theory and Methods: The proposed method extends the nonlocal means algorithm to adapt the influence of the original pixel value according to a simple measure for patch regularity. Detail preservation is improved by a compactly supported weighting kernel that closely approximates the commonly used exponential weight, while an oracle step ensures efficient background noise removal. Denoising experiments were conducted on real-time images of healthy subjects reconstructed by regularized nonlinear inversion from radial acquisitions with pronounced undersampling. Results: The filter leads to a signal-to-noise ratio (SNR) improvement of at least 60% without noticeable artifacts or loss of detail. The method visually compares to more complex state-of-the-art filters as the block-matching three-dimensional filter and in certain cases better matches the underlying noise model. Acceleration of the computation to more than 100 complex frames per second using graphics processing units is straightforward. Conclusion: The sensitivity of nonlocal means to small details can be significantly increased by the simple strategies presented here, which allows partial restoration of SNR in iteratively reconstructed images without introducing a noticeable time delay or image artifacts. © 2016 Wiley Periodicals, Inc. Source


Schweisfurth M.A.,Biomedizinische Nmr Forschungs Gmbh Am Max Planck Institute For Biophysikalische Chemie | Schweisfurth M.A.,German Primate Center | Frahm J.,Biomedizinische Nmr Forschungs Gmbh Am Max Planck Institute For Biophysikalische Chemie | Schweizer R.,Biomedizinische Nmr Forschungs Gmbh Am Max Planck Institute For Biophysikalische Chemie
Frontiers in Human Neuroscience | Year: 2014

This study determined the individual maps of all fingers in Brodmann area 3b of the human primary somatosensory cortex in a single fMRI session by tactile stimulation at 19 sites across all phalanges and digit bases of the 5 right-hand digits. To quantify basic features of the digit maps within and across subjects, we applied standard descriptive measures, but also implemented a novel quantitative analysis. This so-called Direction/Order (DiOr) method tested whether subjects exhibited an ordering of peak fMRI representations along their individual direction of alignment through the set of analyzed phalanges and whether these individual directions were similar across subjects. Across-digit analysis demonstrated that for each set of homologous phalanges, the D5-to-D1 representations were successively represented along a common direction of alignment. Hence, the wellknown mediolateral D5-to-D1 somatotopy was not only confirmed for the distal phalanges (p1), but could also be shown for the medial (p2) and proximal phalanges (p3). In contrast, the peak activation for the digit bases (p4) only partly elicited that digit succession. Complementary, intra-digit analysis revealed a divergent picture of map topography for the different digits. Within D5 (and in a trend: D4), an ordered p1-to-p3 succession was found across subjects, pointing to a consistent intra-digit somatotopy for D5, with p3 generally found medial-posterior to p1. In contrast, for D1, D2, and D3, most subjects did not present with ordered p1-to-p3 maps nor were directions of alignment similarly oriented between subjects. These digits therefore exhibited highly diverse representation patterns across subjects. © 2014 Schweis furth, Frahm and Schweizer. Source


Hofer S.,Biomedizinische Nmr Forschungs Gmbh Am Max Planck Institute For Biophysikalische Chemie | Karaus A.,Biomedizinische Nmr Forschungs Gmbh Am Max Planck Institute For Biophysikalische Chemie | Frahm J.,Biomedizinische Nmr Forschungs Gmbh Am Max Planck Institute For Biophysikalische Chemie
Frontiers in Neuroanatomy | Year: 2010

The human visual system comprises elongated fiber pathways that represent a serious challenge for diffusion tensor imaging (DTI) and fiber tractography: while tracking of frontal fiber bundles may be compromised by the nearby presence of air-filled cavities, nerves, and eye muscles, the anatomic courses of the three main fiber bundles of the optic radiation are subject to pronounced inter-subject variability. Here, tractography of the entire visual pathway was achieved in six healthy subjects at high spatial accuracy, that is, at 1.8 mm isotropic spatial resolution, without susceptibility-induced distortions, and in direct correspondence to anatomic MRI structures. Using a newly developed diffusion-weighted single-shot STEAM MRI sequence, we were able to track the thin optic nerve including the nasal optic nerve fibers, which cross the optic chiasm, and to dissect the optic radiation into the anterior ventral bundle (Meyer's loop), the central bundle, and the dorsal bundle. Apart from scientific applications these results in single subjects promise advances in the planning of neurosurgical procedures to avoid unnecessary damage to the visual fiber system. Source


Watanabe T.,Biomedizinische Nmr Forschungs Gmbh Am Max Planck Institute For Biophysikalische Chemie | Frahm J.,Biomedizinische Nmr Forschungs Gmbh Am Max Planck Institute For Biophysikalische Chemie | Michaelis T.,Biomedizinische Nmr Forschungs Gmbh Am Max Planck Institute For Biophysikalische Chemie
Brain Structure and Function | Year: 2014

Using T1-weighted MRI at two different magnetic field strengths, the enhanced longitudinal relaxivity due to paramagnetic manganese ions in mouse brain in vivo is shown to reflect reduced intracellular mobility. One day after systemic administration of manganese chloride, increases of the longitudinal relaxation rate {increment}R1 in several brain regions are significantly higher at 2.35 T than at 9.4 T. The corresponding relaxivity ratios 100r1/400r1 = 100{increment}R1/400{increment}R1 range from 2.4 (striatum) to 4.4 (cerebellar cortex). In contrast, the {increment}R1 values after intraventricular administration of gadolinium-DTPA (Gd-DTPA) are not significantly different between both field strengths yielding 100r1/400r1 ratios from 1.0 to 1.1. The same observation holds true for manganese and Gd-DTPA relaxivities in aqueous solution. The pronounced field strength dependence of manganese relaxivities indicates a reduced mobility of manganese ions in vivo by confinement to a viscous fluid compartment and/or due to macromolecular binding. Moreover, preferential enhancement of nerve cell assemblies by manganese ions and the observation of additional contrast enhancement by magnetization transfer suggest an intracellular localization of manganese. This is further supported by a slow release of manganese from nerve cells postmortem, which occurs despite a high permeability of damaged cellular membranes as demonstrated by a rapid uptake of extracellular Gd-DTPA. © 2014 Springer-Verlag Berlin Heidelberg. Source

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