Biomedizinische Nmr Forschungs Gmbh Am Max Planck Institute For Biophysikalische Chemie

Gottingen, Germany

Biomedizinische Nmr Forschungs Gmbh Am Max Planck Institute For Biophysikalische Chemie

Gottingen, Germany

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


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.


Niebergall A.,Biomedizinische Nmr Forschungs Gmbh Am Max Planck Institute For Biophysikalische Chemie | Zhang S.,Biomedizinische Nmr Forschungs Gmbh Am Max Planck Institute For Biophysikalische Chemie | Kunay E.,University of Gottingen | Keydana G.,University of Gottingen | And 3 more authors.
Magnetic Resonance in Medicine | Year: 2013

Dynamic MRI studies of the upper airway during speaking, singing or swallowing are complicated by the need for high temporal resolution and the presence of air-tissue interfaces that may give rise to image artifacts such as signal void and geometric distortions. This work exploits a recently developed real-time MRI technique to address these challenges for monitoring speech production at 3 T. The method combines a short-echo time radial FLASH MRI sequence (pulse repetition time/echo time = 2.22/1.44 ms; flip angle 5°) with pronounced undersampling (15 radial spokes per image) and image reconstruction by regularized nonlinear inversion. The resulting serial images at 1.5 mm in-plane resolution and 33.3 ms acquisition time are free of motion or susceptibility artifacts. This application focuses on a dynamic visualization of the main articulators during natural speech production (Standard Modern German). Respective real-time MRI movies at 30 frames per second clearly demonstrate the spatiotemporal coordination of lips, tongue, velum, and larynx for generating vowels, consonants, and coarticulations. The quantitative results for individual phonetic events are in agreement with previous non-MRI findings. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc. Copyright © 2012 Wiley Periodicals, Inc.


Dreha-Kulaczewski S.,University of Gottingen | Joseph A.A.,Biomedizinische Nmr Forschungs Gmbh Am Max Planck Institute For Biophysikalische Chemie | Joseph A.A.,German Center for Cardiovascular Research | Merboldt K.-D.,Biomedizinische Nmr Forschungs Gmbh Am Max Planck Institute For Biophysikalische Chemie | And 4 more authors.
Journal of Neuroscience | Year: 2015

The mechanisms behind CSF flow in humans are still not fully known. CSF circulates from its primary production sites at the choroid plexus through the brain ventricles to reach the outer surface of the brain in the subarachnoid spaces from where it drains into venous bloodstream and cervical lymphatics. According to a recent concept of brain fluid transport, established in rodents, CSF from the brain surface also enters the brain tissue along para-arterial routes and exits through paravenous spaces again into subarachnoid compartments. This unidirectional flow is mainly driven by arterial pulsation. To investigate how CSF flow is regulated in humans, we applied a novel real-time magnetic resonance imaging technique at high spatial (0.75 mm) and temporal (50 ms) resolution in healthy human subjects. We observed significant CSF flow exclusively with inspiration. In particular, during forced breathing, high CSF flow was elicited during every inspiration, whereas breath holding suppressed it. Only a minor flow component could be ascribed to cardiac pulsation. The present results unambiguously identify inspiration as the most important driving force for CSF flow in humans. Inspiratory thoracic pressure reduction is expected to directly modulate the hydrostatic pressure conditions for the low-resistance paravenous, venous, and lymphatic clearance routes of CSF. Furthermore, the experimental approach opens new clinical opportunities to study the pathophysiology of various forms of hydrocephalus and to design therapeutic strategies in relation to CSF flow alterations. © 2015 the authors.


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.


Sumpf T.J.,Biomedizinische Nmr Forschungs Gmbh Am Max Planck Institute For Biophysikalische Chemie | Uecker M.,Biomedizinische Nmr Forschungs Gmbh Am Max Planck Institute For Biophysikalische Chemie | Boretius S.,Biomedizinische Nmr Forschungs Gmbh Am Max Planck Institute For Biophysikalische Chemie | Frahm J.,Biomedizinische Nmr Forschungs Gmbh Am Max Planck Institute For Biophysikalische Chemie
Journal of Magnetic Resonance Imaging | Year: 2011

Purpose: To develop a model-based reconstruction technique for T2 mapping based on multi-echo spin-echo MRI sequences with highly undersampled Cartesian data encoding. Materials and Methods: The proposed technique relies on a nonlinear inverse reconstruction algorithm which directly estimates a T2 and spin-density map from a train of undersampled spin echoes. The method is applicable to acquisitions with single receiver coils but benefits from multi-element coil arrays. The algorithm is validated for trains of 16 spin echoes with a spacing of 10 to 12 ms using numerical simulations as well as human brain MRI at 3 Tesla (T). Results: When compared with a standard T2 fitting procedure using fully sampled T2-weighted images, and depending on the available signal-to-noise ratio and number of coil elements, model-based nonlinear inverse reconstructions for both simulated and in vivo MRI data yield accurate T2 estimates for undersampling factors of 5 to 10. Conclusion: This work describes a promising strategy for T2-weighted MRI that simultaneously offers accurate T2 relaxation times and properly T2-weighted images at arbitrary echo times. For a standard spin-echo MRI sequence with Cartesian encoding, the method allows for a much higher degree of undersampling than obtainable by conventional parallel imaging. © 2011 Wiley-Liss, Inc.


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.


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.


Zhang S.,Biomedizinische Nmr Forschungs Gmbh Am Max Planck Institute For Biophysikalische Chemie | Uecker M.,Biomedizinische Nmr Forschungs Gmbh Am Max Planck Institute For Biophysikalische Chemie | Voit D.,Biomedizinische Nmr Forschungs Gmbh Am Max Planck Institute For Biophysikalische Chemie | Merboldt K.-D.,Biomedizinische Nmr Forschungs Gmbh Am Max Planck Institute For Biophysikalische Chemie | Frahm J.,Biomedizinische Nmr Forschungs Gmbh Am Max Planck Institute For Biophysikalische Chemie
Journal of Cardiovascular Magnetic Resonance | Year: 2010

Background. Functional assessments of the heart by dynamic cardiovascular magnetic resonance (CMR) commonly rely on (i) electrocardiographic (ECG) gating yielding pseudo real-time cine representations, (ii) balanced gradient-echo sequences referred to as steady-state free precession (SSFP), and (iii) breath holding or respiratory gating. Problems may therefore be due to the need for a robust ECG signal, the occurrence of arrhythmia and beat to beat variations, technical instabilities (e.g., SSFP "banding" artefacts), and limited patient compliance and comfort. Here we describe a new approach providing true real-time CMR with image acquisition times as short as 20 to 30 ms or rates of 30 to 50 frames per second. Methods. The approach relies on a previously developed real-time MR method, which combines a strongly undersampled radial FLASH CMR sequence with image reconstruction by regularized nonlinear inversion. While iterative reconstructions are currently performed offline due to limited computer speed, online monitoring during scanning is accomplished using gridding reconstructions with a sliding window at the same frame rate but with lower image quality. Results. Scans of healthy young subjects were performed at 3 T without ECG gating and during free breathing. The resulting images yield T1 contrast (depending on flip angle) with an opposed-phase or in-phase condition for water and fat signals (depending on echo time). They completely avoid (i) susceptibility-induced artefacts due to the very short echo times, (ii) radiofrequency power limitations due to excitations with flip angles of 10° or less, and (iii) the risk of peripheral nerve stimulation due to the use of normal gradient switching modes. For a section thickness of 8 mm, real-time images offer a spatial resolution and total acquisition time of 1.5 mm at 30 ms and 2.0 mm at 22 ms, respectively. Conclusions. Though awaiting thorough clinical evaluation, this work describes a robust and flexible acquisition and reconstruction technique for real-time CMR at the ultimate limit of this technology. © 2010 Zhang et al; licensee BioMed Central Ltd.


Zhang S.,Biomedizinische Nmr Forschungs Gmbh Am Max Planck Institute For Biophysikalische Chemie | Block K.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
Journal of Magnetic Resonance Imaging | Year: 2010

Purpose: To develop technical advances for real-time magnetic resonance imaging (MRI) that allow for improved image quality and high frame rates. Materials and Methods: The approach is based on a combination of fast low-angle shot (FLASH) MRI sequences with radial data sampling and view sharing of successive acquisitions. Gridding reconstructions provide images free from streaking or motion artifacts and with a flexible trade-off between spatial and temporal resolution. Immediate image reconstruction and online display is accomplished with the use of an unmodified 3 T MRI system. For receive coils with a large number of elements this process is supported by a user-selectable channel compression that is based on a principal component analysis and performed during initial preparation scans. Results: In preliminary applications to healthy volunteers, real-time radial FLASH MRI visualized continuous movements of the temporomandibular joint during voluntary opening and closing of the mouth at high spatial resolution (0.75 mm in-plane) and monitored cardiac functions at high temporal resolution (20 images per second) during free breathing and without synchronization to the electrocardiogram. Conclusion: Real-time radial FLASH MRI emerges as a simple and versatile tool for a large range of clinical applications. © 2009 Wiley-Liss, Inc.

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