Papers by Karl-heinz Herrmann
Diagnostics, 2021
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Pediatric Transplantation, 2019
This is an open access article under the terms of the Creative Commons Attribution License, which... more This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
The Journal of Neuroscience, 2016
The clustered architecture of the brain for different visual stimulus categories is one of the mo... more The clustered architecture of the brain for different visual stimulus categories is one of the most fascinating topics in the cognitive neurosciences. Interestingly, recent research suggests the existence of additional regions for newly acquired stimuli such as letters (letter form area; LFA; Thesen et al., 2012) and numbers (visual number form area; NFA; Shum et al., 2013). However, neuroimaging methods thus far have failed to visualize the NFA in healthy participants, likely due to fMRI signal dropout caused by the air/bone interface of the petrous bone (Shum et al., 2013). In the current study, we combined a 64-channel head coil with high spatial resolution, localized shimming, and liberal smoothing, thereby decreasing the signal dropout and increasing the temporal signal-to-noise ratio in the neighborhood of the NFA. We presented subjects with numbers, letters, false numbers, false letters, objects and their Fourier randomized versions. A group analysis showed significant activa...
Zeitschrift für Medizinische Physik, 2005
The aim of this study was to develop and implement an algorithm for the co-registration of 3D bre... more The aim of this study was to develop and implement an algorithm for the co-registration of 3D breast MRI sets acquired at two slightly different patient positions (repetitive examination). Combined translation and rotation with locally varying parameters were applied for the purpose of coordinate transformation. A phantom allowing selective changes of the volume of the glandular tissue model was developed, in order to prove the robustness of the proposed matcher against local changes. Serial 3D data sets of phantoms and volunteers were acquired to validate the routines. Co-registration was performed using mutual information (MI) as a similarity measure of the matching of the acquired images. In the phantom study, the phantom was deliberately shifted and rotated around horizontal and vertical axes. Starting the registration with global translations using a rigid matcher, the horizontal (φ) and vertical (θ) rotation angles were optimized in an iteration loop for each slice. This method was then applied to the breast data sets. Application of the algorithm on serial 3D MR data sets improved the co-registration especially in consideration of varying local tissue volumes. The algorithm represents a compromise between a pure rigid and an elastic 3D matcher.
Clinical Neurophysiology, 2014
ilar age underwent clinical neurological evaluation and muscle ultrasound only. DRKS00000642 Resu... more ilar age underwent clinical neurological evaluation and muscle ultrasound only. DRKS00000642 Results: Nerve conduction studies showed typical measurements for CIP. Ultrasonic echo intensity of muscles was graded semiquantitatively in 4 grades. In muscles of proximal and distal upper and lower extremities the detection of fasciculations was evaluated. 75% of patients showed a mean echotexture greater than 1.5, which was the maximal value found in the control group. A significant difference in mean muscle echotexture between patients and controls were found at day 4 and day 14 (both p<0.001). In addition, from day 4 to day 14 the mean grades of muscle echotexture increased in the patient group (p=0.085). Healthy controls revealed the lowest number of fasciculations (in 7 to 10% in proximal and distal arms and proximal leg, 38% in the distal leg). Patients revealed more muscular regions in which fasciculations were detected in comparison to controls (p=0.08 at day 4 and p=0.002 at day 14). Conclusion: Muscle ultrasound is an easily applicable, non-invasive diagnostic tool to evaluate muscle and nerve impairment in patients with severe sepsis in the intensive care unit and could be an additive tool to gold standard, but more invasive techniques such as electromyography and/or muscle biopsy.
Biomedical Engineering / Biomedizinische Technik, 2012
Multimodal imaging (e.g. MRI and optical imaging) with targeted nanoparticle based magneto-optica... more Multimodal imaging (e.g. MRI and optical imaging) with targeted nanoparticle based magneto-optical probes allows for detection of a broad range of molecular-cellular targets through their modular design. Here, we propose the construction multimodal probes addressing mVCAM-1 expression on endothelial cells as response to inflammatory factors. Targeted multimodal nanoparticle probes were designed consisting of 3 components: an iron oxide core derivatized with dextran (with and without PEG-linker), antibodies directed to the cell-surface molecule VCAM-1, and a nearinfrared fluorochrome (DY-649). Physicochemical and cell-binding properties of the probes were evaluated on murine endothelial cells. After the conjugation of anti-VCAM-1 antibody/DY-649 constructs (2.2-3.1 nmol antibody/mg Fe and 2.6-4.6 nmol DY-649/mg Fe) to the magnetic nanoparticles, the hydrodynamic diameters of the nanoparticles increased slightly. No aggregations of the probes were detectable, their corresponding relaxivities were r1 = 7.8-8.4 1/mM/s, r2 = 180-325 1/mM/s and r2* = 274-348 1/mM/s. Using optical imaging, the VCAM-1 targeted magneto-optical probes gave detectable fluorescence signals after binding to murine endothelial cells, the signals decreased by blocking with unlabelled anti-mVCAM-1 antibodies. This observation demonstrates the specific binding properties of the designed VCAM-1 specific bimodal nanoparticle based probes. We showed that it is possible to produce multimodal magnetic nanoparticles selectively addressing mVCAM-1 on endothelial cells by conjugation of DY-649-labelled antibodies to magnetic nanoparticles. Our probes exhibit good capabilities to be used as a probe in multimodal imaging approaches of diseases with increased mVCAM-1-expression (e.g. inflammation) with MRI and optical imaging in murine animal models.
Magnetic Resonance Imaging, 2008
To enhance susceptibility-related contrast of magnetic resonance images, the phase of susceptibil... more To enhance susceptibility-related contrast of magnetic resonance images, the phase of susceptibility weighted data needs to be corrected for background inhomogeneities and phase wraps caused by them. Current methods either use homodyne filtering or a combination of phase unwrapping and high pass filtering. The drawback of homodyne filtering is incomplete elimination of phase wraps in areas with steep phase topography produced by background inhomogeneities of the static magnetic field. The disadvantage of phase unwrapping is that it requires subsequent high pass filtering, which introduces artifacts in areas with very steep transitions, such as areas near interfaces between parenchyma and bone or air. A method is proposed that reduces the artifacts associated with high pass filtering without sacrificing the advantages of phase unwrapping. This technique is demonstrated with phantom data at 1.
NeuroImage, 2009
Withdrawn 403 F-AM EEG-topography informed BOLD activations reveal the anatomical segregation of ... more Withdrawn 403 F-AM EEG-topography informed BOLD activations reveal the anatomical segregation of four large-scale functional networks at rest, J.
Journal of Hydrology, 2002
We report on the use of a pulsed gradient spin-echo imaging sequence for the three-dimensional (3... more We report on the use of a pulsed gradient spin-echo imaging sequence for the three-dimensional (3D) imaging of water transport properties in two porous media: 2 mm glass-beads and 0.15 mm quartz-sand mixed with 2 mm glass-beads. In contrast to tracer methods, which monitor the tracer motion by its effect on the signal relaxation of 1 H, this sequence measures the echo signal intensity I 0 without and I with applied diffusion gradient, respectively. For the wide-pore glass-bead system, the intensity loss is controlled by nearly free self-diffusion in the pores. A mean apparent diffusion coefficient is calculated from the ratio lnðI 0 =IÞ as kD loc l ¼ 1:9 £ 10 29 m 2 s 21 ; which is slightly lower than that of free water ðD ¼ 2:3 £ 10 29 m 2 s 21 Þ: Increasing the mean pore flow velocity from 0 to 0.14 mm s 21 results in a linear increase of kD loc l to 2.3 £ 10 29 m 2 s 21 , caused by mechanical dispersion. The spatial distribution is of the log-normal type, where the width increases with increasing pore velocity. Correlation lengths are also calculated. For the fine porous medium, frequent contacts of the water molecules with the pore boundaries lead to a significant decrease of I 0 by increased T 2 relaxation. The resulting ratio of the signal intensities lnðI 0 =IÞ is then smaller than expected for pure diffusion, which is caused by the restricted diffusion in the fine pore system. The spatial distribution (normal) is broader than for the glass-bead system and the mean local apparent diffusion coefficient is calculated as 1 £ 10 29 m 2 s 21 , a dependence on the pore flow velocity could not be detected. For the glass-bead system, the 3D image clearly shows regions of increased dispersivity (50% greater than the kD loc l), caused by packing errors, leading to preferential flow. This macroscopic effect on the column scale is quantified by a numerical simulation of tracer transport, based on the 3D diffusion coefficient field, assuming a linear relation to local velocities. From this simulation, the effective dispersion coefficient is obtained for the column scale ðD eff ¼ 130 £ 10 29 m 2 s 21 Þ; which is comparable to that obtained from classical breakthrough curves with tracer substances.
Biomedizinische Technik/Biomedical Engineering, 2008
An increasing number of animal experiments are currently conducted on clinical MR systems. Motion... more An increasing number of animal experiments are currently conducted on clinical MR systems. Motion artefacts due to breathing can become quite apparent, in particular with abdominal examinations. These artefacts can be reduced by using a triggered acquisition. However, the built-in detectors in human whole-body scanners are usually not sensitive enough to detect the tiny movements of small rodents. Therefore, a sensitive optical motion detector was developed together with a simple, robust analogue circuit. This circuit converts the original optical signal into an electrical one, compensates slow drifts and offsets, and finally generates a transistortransistor logic trigger signal as input for the clinical whole-body magnetic resonance scanner. The trigger was successfully applied in mouse experiments.
NMR in Biomedicine, 2013
In the past, spin-echo (SE) echo planar imaging(EPI)-based diffusion tensor imaging (DTI) has bee... more In the past, spin-echo (SE) echo planar imaging(EPI)-based diffusion tensor imaging (DTI) has been widely used to study the fiber structure of skeletal muscles in vivo. However, this sequence has several shortcomings when measuring restricted diffusion in small animals, such as its sensitivity to susceptibility-related distortions and a relatively short applicable diffusion time. To address these limitations, in the current work, a stimulated echo acquisition mode (STEAM) MRI technique, in combination with fast low-angle shot (FLASH) readout (turbo-STEAM MRI), was implemented and adjusted for DTI in skeletal muscles. Signal preparation using stimulated echoes enables longer effective diffusion times, and thus the detection of restricted diffusion within muscular tissue with intracellular distances up to 100 μm. Furthermore, it has a reduced penalty for fast T 2 muscle signal decay, but at the expense of 50% signal loss compared with a SE preparation. Turbo-STEAM MRI facilitates high-resolution DTI of skeletal muscle without introducing susceptibility-related distortions. To demonstrate its applicability, we carried out rabbit in vivo measurements on a human whole-body 3 T scanner. DTI parameters of the shank muscles were extracted, including the apparent diffusion coefficient, fractional anisotropy, eigenvalues and eigenvectors. Eigenvectors were used to calculate maps of structural parameters, such as the planar index and the polar coordinates θ and φ of the largest eigenvector. These parameters were compared between three muscles. θ and φ showed clear differences between the three muscles, reflecting different pennation angles of the underlying fiber structures. Fiber tractography was performed to visualize and analyze the architecture of skeletal pennate muscles. Optimization of tracking parameters and utilization of T 2-weighted images for improved muscle boundary detection enabled the determination of additional parameters, such as the mean fiber length. The presented results support the applicability of turbo-STEAM MRI as a promising method for quantitative DTI analysis and fiber tractography in skeletal muscles.
Vascularisation is an important marker for the diagnosis of breast tumors. MR Mammography (MRM) i... more Vascularisation is an important marker for the diagnosis of breast tumors. MR Mammography (MRM) is therefore used as a non-invasive, versatile method to characterize both microvessel density and macroscopic vascularity [1]. Although there is ample evidence that the overall vascularity is an indicator for tumor type and grade, separation of arteries from venous vessels is often hindered due to the distribution of the contrast agent in the vasculature and the loss of temporal information about the first-pass. However, the ability to resolve the first-pass dynamics, while still acquiring contrast-enhanced data following established protocols, might further improve the specificity of the method.
Zeitschrift für medizinische Physik, 2014
Performing magnetic resonance imaging (MRI) experiments with small animals requires continuous mo... more Performing magnetic resonance imaging (MRI) experiments with small animals requires continuous monitoring of vital parameters, especially the respiration rate. Clinical whole-body MR scanners represent an attractive option for preclinical imaging as dedicated animal scanners are cost-intensive in both investment and maintenance, thus limiting their availability. Even though impressive image quality is achievable with clinical MR systems in combination with special coils, their built-in physiologic monitoring and triggering units are often not suited for small animal imaging. In this work, we present a simple, MRI compatible low cost solution to monitor the respiration and heart rate of small animals in a clinical whole-body MR scanner. The recording and processing of the biosignals as well as the optimisation of the respiratory trigger generation is decribed. Additionally rat and mouse in-vivo MRI experiments are presented to illustrate the effectiveness of the monitoring and respir...
Journal of Visualized Experiments, 2014
The rodent visual system encompasses retinal ganglion cells and their axons that form the optic n... more The rodent visual system encompasses retinal ganglion cells and their axons that form the optic nerve to enter thalamic and midbrain centers, and postsynaptic projections to the visual cortex. Based on its distinct anatomical structure and convenient accessibility, it has become the favored structure for studies on neuronal survival, axonal regeneration, and synaptic plasticity. Recent advancements in MR imaging have enabled the in vivo visualization of the retino-tectal part of this projection using manganese mediated contrast enhancement (MEMRI). Here, we present a MEMRI protocol for illustration of the visual projection in mice, by which resolutions of (200 µm) 3 can be achieved using common 3 Tesla scanners. We demonstrate how intravitreal injection of a single dosage of 15 nmol MnCl 2 leads to a saturated enhancement of the intact projection within 24 hr. With exception of the retina, changes in signal intensity are independent of coincided visual stimulation or physiological aging. We further apply this technique to longitudinally monitor axonal degeneration in response to acute optic nerve injury, a paradigm by which Mn 2+ transport completely arrests at the lesion site. Conversely, active Mn 2+ transport is quantitatively proportionate to the viability, number, and electrical activity of axon fibers. For such an analysis, we exemplify Mn 2+ transport kinetics along the visual path in a transgenic mouse model (NF-κB p50 KO) displaying spontaneous atrophy of sensory, including visual, projections. In these mice, MEMRI indicates reduced but not delayed Mn 2+ transport as compared to wild type mice, thus revealing signs of structural and/or functional impairments by NF-κB mutations. In summary, MEMRI conveniently bridges in vivo assays and post mortem histology for the characterization of nerve fiber integrity and activity. It is highly useful for longitudinal studies on axonal degeneration and regeneration, and investigations of mutant mice for genuine or inducible phenotypes.
NeuroImage, 2012
Traditionally, depiction of isolated CNS fiber tracts is achieved by histological post mortem stu... more Traditionally, depiction of isolated CNS fiber tracts is achieved by histological post mortem studies. As a tracerdependent strategy, the calcium analog manganese has proved valuable for in vivo imaging of CNS trajectories, particularly in rats. However, adequate protocols in mice are still rare. To take advantage of the numerous genetic mouse mutants that are available to study axonal de-and regeneration processes, a MnCl 2-based protocol for high-resolution contrast-enhanced MRI (MEMRI) of the visual pathway in mice acquired on a widely used clinical 3 Tesla scanner was established. Intravitreal application of MnCl 2 significantly enhanced T1-weighted contrast and signal intensity along the retino-petal projection enabling its reconstruction in a 3D mode from a maximum intensity projection (MIP) calculated dataset. In response to crush injury of the optic nerve, axonal transport of MnCl 2 was diminished and completely blocked proximal and distal to the lesion site, respectively. Conditions of Wallerian degeneration after acute optic nerve injury accelerated Mn 2+-enhanced signal fading in axotomized projection areas between 12 and 24 h post-injury. In long-term regeneration studies 12 months after optic nerve injury, the MRI protocol proved highly sensitive and discriminated animals with rare spontaneous axonal regrowth from non-regenerating specimens. Also, structural MRI aspects shared high correlation with histological results in identical animals. Moreover, in a model of chronic neurodegeneration in p50/NF-κBdeficient mice, MnCl 2-based neuron-axonal tracing supported by heat map imaging indicated neuropathy of the visual pathway due to atrophy of optic nerve fiber projections. Toxic effects of MnCl 2 at MRI contrast-relevant dosages in repetitive administration protocols were ruled out by histological and optometric examinations. At higher dosages, photoreceptors, not retinal ganglion cells, turned out as most susceptible to the well-known toxicity of MnCl 2. Our data accentuate in vivo MEMRI of the murine visual system as a highly specific and sensitive strategy to uncover axonal degeneration and restoration processes, even in a functional latent state. We expect MEMRI to be promising for future applications in longitudinal studies on development, aging, or regeneration of CNS projections in mouse models mimicking human CNS pathologies.
Journal of Magnetism and Magnetic Materials, 2007
This work investigated macrophages labeled with magnetosomes for the possible detection of inflam... more This work investigated macrophages labeled with magnetosomes for the possible detection of inflammations by MR molecular imaging. Pure magnetosomes and macrophages containing magnetosomes were analyzed using a clinical 1.5 T MR-scanner. Relaxivities of magnetosomes and relaxation rates of cells containing magnetosomes were determined. Peritonitis was induced in two mice. T 1 , T 2 and T 2 * weighted images were acquired following injection of the probes. Pure magnetosomes and labeled cells showed slight effects on T 1 , but strong effects on T 2 and T 2 * images. Labeled macrophages were located with magnetic resonance imaging (MRI) in the colon area, thus demonstrating the feasibility of the proposed approach.
Journal of Environment Quality, 2002
dimensional flow fields (see below). Besides others, one versatile approach for modeling three-di... more dimensional flow fields (see below). Besides others, one versatile approach for modeling three-dimensional The transport of Ni 2؉ ions in a column, filled with porous media, transport processes is the use of particle tracking. Partiwas observed in three dimensions and time by magnetic resonance imaging (MRI) in a clinical scanner. For porous media we used glass cle tracking models like PARTRACE (Neuendorf, beads or quartz sand in a saturated continuous flow mode. The mag-1997) use a divergence-free heterogenous flow velocity netic moment of Ni 2؉ decreased the T 1 relaxation time of 1 H in aqueous field as input for transport modeling. The local flow solution. This concentration-dependent effect was used by a fast low properties have to be determined by either a modeling angle shot (FLASH) MRI sequence for imaging the concentration of program like TRACE (Seidemann, 1997) or by direct the dissolved ions. Since Ni 2؉ behaves as a conservative tracer under measurement of the local flow velocities, which can be the chosen conditions, the tracer motion was representative for the achieved by the presented MRI experiments. PARwater flow in the porous medium. Currently, we can achieve an iso-TRACE then will divide the total tracer mass in little tropic spatial resolution of 1.5 mm and a temporal resolution of 170 s. particles, each representing a fraction of the total tracer The transport observation gives direct access to hydraulic flow propermass, which are tracked on their way through the modties of the porous media. The fluid flow velocity field was calculated by a fronttracking method and the statistical properties of the veloci-eled porous medium according to the local flow velocities were investigated. We also compared the experimental data with ties. At each timestep, new local free and sorbed concenthe three-dimensional particle tracking model PARTRACE, which trations are calculated from the particle positions. uses the experimental flow field as input. Models like PARTRACE are quite capable of describing even very complex interactions between flow and chemical heterogeneity but have high demands on
European Journal of Human Genetics, 2013
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Papers by Karl-heinz Herrmann