Biomedical subjects

A Haase

Publications and source records attributed to A Haase.

At least 37 records · Page 2Linked to original sources

PubMed2001

VD-AUTO-SMASH imaging.

Recently a self-calibrating SMASH technique, AUTO-SMASH, was described. This technique is based on PPA with RF coil arrays using auto-calibration signals. In AUTO-SMASH, important coil sensitivity information required for successful SMASH reconstruction is obtained during the actual scan using the correlation between undersampled SMASH signal data and additionally sampled calibration signals with appropriate offsets in k-space. However, AUTO-SMASH is susceptible to noise in the acquired data and to imperfect spatial harmonic generation in the underlying coil array. In this work, a new modified type of internal sensitivity calibration, VD-AUTO-SMASH, is proposed. This method uses a VD k-space sampling approach and shows the ability to improve the image quality without significantly increasing the total scan time. This new k-space adapted calibration approach is based on a k-space-dependent density function. In this scheme, fully sampled low-spatial frequency data are acquired up to a given cutoff-spatial frequency. Above this frequency, only sparse SMASH-type sampling is performed. On top of the VD approach, advanced fitting routines, which allow an improved extraction of coil-weighting factors in the presence of noise, are proposed. It is shown in simulations and in vivo cardiac images that the VD approach significantly increases the potential and flexibility of rapid imaging with AUTO-SMASH.

Artifacts↗

PubMed2001

Perfusion imaging using spin-labeling methods: contrast-to-noise comparison in functional MRI applications.

In this study the performance of FLASH imaging with selective inversion preparation for functional perfusion studies was investigated. In addition to the absolute quantification of perfusion by measurement of the longitudinal relaxation times with global (T(1glob)) and selective (T(1sel)) inversion, the measurement of absolute (BASE) and relative (FAIR) perfusion increases by subtraction of appropriately weighted images was also considered. The subject averages of absolute perfusion obtained by the quantitative method were 70.7 +/- 4.0 ml/100g/min in gray matter, 10.2 +/- 3.4 ml/100g/min in white matter, and 89.0 +/- 3.1 ml/100g/min in visual cortex. These values, as well as the average increase of perfusion due to visual stimulation (44.4 +/- 3.7 ml/100g/min), agree well with respective data reported by PET and other MRI studies. However, for individual subjects the standard deviations over single ROIs inside the visual cortex lay around 100% which prevented the detection of significant activation. BASE and FAIR, on the other hand, were able to detect significant activation in single subjects. The measured average perfusion increases were 51.7 +/- 6.6 ml/100g/min and 56.5 +/- 13.8%, respectively. Magn Reson Med 46:172-182, 2001.

Adult↗

PubMed2001

Combined high-speed NMR imaging of perfusion and microscopic coronary conductance vessels in the isolated rat heart.

Noninvasive characterization of microcirculation at the level of both coronary conductance and resistance vessels is of major importance for the understanding of microvascular adaptive processes in the heart. The objective of this study was to determine simultaneously myocardial perfusion and microvessel diameters in the myocardium by magnetic resonance (MR) imaging within the same heart. A MR imaging method is presented which combines high-resolution perfusion measurement (140 x 140 microm2) by spin labeling with flow-weighted MR microscopy of coronary microvessels (phi > 140 microm). We determined changes in myocardial perfusion and vessel diameters of isolated beating rat hearts (n = 10) at rest and during administration of nitroglycerin (0.5 mg/min). Alterations in perfusion were validated by microsphere measurements. Under the influence of nitroglycerin an increase in perfusion (+2.51 +/- 0.4 ml x min(-1) x g(-1), mean +/- SEM) and vessel diameters (+14.22 +/- 1.92%) could be observed. Endocardial perfusion revealed a modest enhanced susceptibility to nitroglycerin in comparison to epicardial perfusion. Analysis of vessels according to their diameters showed no significant differences. MR imaging allows the noninvasive and simultaneous determination of conducting arteries and smaller resistance vessels in one and the same beating rat heart. Due to an excellent spatial resolution of these methods, transmural characterization of both parameters at rest and during vasodilation is feasible.

Animals↗

PubMed2001

In vivo 19F NMR chemical-shift imaging of Ancistrocladus species.

19F nuclear magnetic resonance (NMR) imaging and 19F NMR chemical-shift imaging (19F CSI) have been used to localize fluorinated compounds administered to stems of Ancistrocladus heyneanus and A. abbreviatus for the elucidation of biosynthetic pathways in living plants. This first application of 19F CSI on plants proved CSI to be a valuable technique for mapping fluorinated molecules in plants. Exemplarily using trifluoroacetate as a model compound allowed to select appropriate feeding methods and to optimize both concentration and duration of the application to the plant. The time course of the uptake and distribution of trifluoroacetate was monitored by both 19F imaging and 19F CSI. Fluorinated metabolites formed by uptake of 3-fluoro-3-deoxy-D-glucose were detected with 19F CSI.

Fluorine↗

PubMed2001

Fast three-dimensional sodium imaging of human brain.

A three-dimensional sodium imaging technique with a minimum echo time of 0.9 ms is described in a 2.0 Tesla whole-body system. The relaxation behaviour in vivo of sodium was analysed: a fast T(2)(*) relaxation component between 1.2 and 1.6 ms and a slow T(2)(*) relaxation component between 7.1 ms and 8.4 ms were quantified in brain tissue of three volunteers. Three-dimensional sodium images of the human brain were acquired in 8.5 min with a resolution of 4.7 x 4.7 x 10 mm (0.2 cc voxel size) and a signal-to-noise ratio of 20 in brain tissue and 30 in cerebrospinal fluid.

Biophysics↗

PubMed2001

A tissue-specific marker of Ecdysozoa.

Over the past few years, molecular studies of phylogeny have challenged the traditional view of evolutionary relationships among protostomian animal phyla. Based on analysis of 18S ribosomal RNA gene sequences, it has been suggested that some traditional groups, like the articulata and the pseudocoelomata, should be completely abandoned and that instead the protostomians should be split into two major clades: the Ecdysozoa and the Lophotrochozoa. However, this new molecular phylogeny still awaits confirmation by independent methods. In this study, we present a cytological feature that supports the new classification. The carbohydrate epitope that is recognised by antisera against the plant glycoprotein horseradish peroxidase (HRP) is known to be selectively expressed by membrane proteins on the surface of neural tissue in insects. We found that the major ecdysozoan phyla show neural expression of HRP immunoreactivity, which is completely absent in the nervous tissue of lophotrochozoans, deuterostomians, and cnidarians. This suggests that the presence of anti-HRP-reactive glycoproteins in neural tissue is an ecdysozoan autapomorphy.

Animals↗

PubMed2001

Myocardial perfusion imaging using a non-contrast agent MR imaging technique.

INTRODUCTION: A MR imaging (MRI) method has been developed to determine quantitatively myocardial perfusion (P) in the rat heart in vivo. This method has the potential to non-invasively measure cardiac perfusion without the use of a contrast agent by exploiting the endogenous contrast from flowing blood itself. METHOD AND RESULTS: Principle of the technique is the arterial spin labeling of endogenous water protons within the short axis imaging slice. Arterial spin labeling techniques are based on a model that uses inflow effects to relate intrinsic changes in longitudinal relaxation (T1) to tissue perfusion. Perfusion is determined from the difference between a slice selective and a global inversion recovery experiment. Perfusion was determined at rest and during hyperemia induced by intravenous adenosine (3 mg/(kg min)). The MR perfusion values were compared with perfusion data obtained in the same animal using the colored microspheres (MS) technique as the gold standard. The MR perfusion (mean +/- SEM) was 3.3 +/- 0.2 ml/min/g at rest and 4.6 +/- 0.6 ml/min/g during adenosine. Perfusion values obtained by colored MS were 3.4 +/- 0.2 and 4.7 +/- 0.8 ml/min/g at rest and during vasodilation, respectively. Adenosine decreased mean arterial pressure (MAP) from 120 to 65 mmHg which implies a reduction of coronary resistance (CR) to about 50% of baseline. CONCLUSION: Our study shows that quantitative mapping of perfusion may be performed non-invasively by MRI. The MR perfusion data are in excellent correlation with data obtained by the well-established colored MS technique. Determination of perfusion reserve confirms that coronary perfusion is highly dependent on blood pressure due to changes in CR.

Animals↗

PubMed2001

Can we use vertical bore magnetic resonance scanners for murine cardiovascular phenotype characterization? Influence of upright body position on left ventricular hemodynamics in mice.

High resolution magnetic resonance (MR) imaging is uniquely suited for cardiovascular phenotype characterization in transgenic mice. Experimental MR scanners with the high magnetic field strength are commonly built with a vertical bore design. The hemodynamic consequences of a prolonged upright body position in anesthetized mice are, however, unknown. Thus, the purpose of this work was to investigate the influence of a vertical body position on murine systemic blood pressure and left ventricular (LV) hemodynamics over time. We studied six C57Bl/6 mice at 14-16 weeks of age (body weight, 24-28 g) under isoflurane anesthesia. Positioned supine on a 37 degrees C warming pad, a microtip catheter was advanced via the right carotid artery into the left ventricle. Continuous registration of LV hemodynamics was performed at rest and after tilting of the table to a 90-degree vertical position. After tilting, there was a transient decrease of LV systolic pressure to 96% of initial values immediately after tilting with return to baseline level within 6 min. Tilting to vertical position had no influence on LV end-diastolic pressure, heart rate, maximal rate of left ventricular pressure increase, and maximal rate of left ventricular pressure decrease. Over a follow-up period of 60 min in vertical position, there were no significant changes in murine hemodynamics. An acute change of body position is fully compensated by a normal orthostatic response in anesthetized mice. Prolonged upright body position exerts no significant changes in murine LV hemodynamics. Hence, high resolution MR studies for cardiovascular phenotype characterization in transgenic mice performed on vertical bore MR scanners allow measurements under physiologic conditions.

Animals↗

PubMed2001

A novel class of amitogenic alginate microcapsules for long-term immunoisolated transplantation.

In the light of results of clinical trials with immunoisolated human parathyroid tissue Ba2+-alginate capsules were developed that meet the requirements for long-term immunoisolated transplantation of (allogeneic and xenogeneic) cells and tissue fragments. Biocompatibility of the capsules was achieved by subjecting high-M alginate extracted from freshly collected brown algae to a simple purification protocol that removes quantitatively mitogenic and cytotoxic impurities without degradation of the alginate polymers. The final ultra-high-viscosity, clinical-grade (UHV/CG) product did not evoke any (significant) foreign body reaction in BB rats or in baboons. Similarly, the very sensitive pERK assay did not reveal any mitogenic impurities. Encapsulated cells also exhibited excellent secretory properties under in vitro conditions. Despite biocompatible material, pericapsular fibrosis is also induced by imperfect capsule surfaces that can favor cell attachment and migration under the release of material traces. This material can interact with free end monomers of the alginate polymers under formation of mitogenic advanced glycation products. Smooth surfaces, and thus topographical biocompatibility of the capsules (visualized by atomic force microscopy), can be generated by appropriate crosslinking of the UHV/CG-alginate with Ba2+ and simultaneous suppression of capsule swelling by incorporation of proteins and/or perfluorocarbons (i.e., medically approved compounds with high oxygen capacity). Perfluorocarbon-loaded alginate capsules allow long-term non-invasive monitoring of the location and the oxygen supply of the transplants by using 19F-MRI. Transplantation studies in rats demonstrated that these capsules were functional over a period of more than two years.

Alginates↗

PubMed2001

A cluster of melioidosis cases from an endemic region is clonal and is linked to the water supply using molecular typing of Burkholderia pseudomallei isolates.

Nine cases of melioidosis with four deaths occurred over a 28-month period in members of a small remote Aboriginal community in the top end of the Northern Territory of Australia. Typing by pulsed-field gel electrophoresis showed isolates of Burkholderia pseudomallei from six of the cases to be clonal and also identical to an isolate from the community water supply, but not to soil isolates. The clonality of the isolates found in this cluster contrasts with the marked genetic diversity of human and environmental isolates found in this region which is hyperendemic for B. pseudomallei. It is possible that the clonal bacteria persisted and were propagated in biofilm in the water supply system. While the exact mode of transmission to humans and the reasons for cessation of the outbreak remain uncertain, contamination of the unchlorinated community water supply is a likely explanation.

Burkholderia pseudomallei↗

PubMed2000

X-ray structure of MalY from Escherichia coli: a pyridoxal 5'-phosphate-dependent enzyme acting as a modulator in mal gene expression.

MalY represents a bifunctional pyridoxal 5'-phosphate-dependent enzyme acting as a beta-cystathionase and as a repressor of the maltose regulon. Here we present the crystal structures of wild-type and A221V mutant protein. Each subunit of the MalY dimer is composed of a large pyridoxal 5'-phosphate-binding domain and a small domain similar to aminotransferases. The structural alignment with related enzymes identifies residues that are generally responsible for beta-lyase activity and depicts a unique binding mode of the pyridoxal 5'-phosphate correlated with a larger, more flexible substrate-binding pocket. In a screen for MalY mutants with reduced mal repressor properties, mutations occurred in three clusters: I, 83-84; II, 181-189 and III, 215-221, which constitute a clearly distinguished region in the MalY crystal structure far away from the cofactor. The tertiary structure of one of these mutants (A221V) demonstrates that positional rearrangements are indeed restricted to regions I, II and III. Therefore, we propose that a direct protein-protein interaction with MalT, the central transcriptional activator of the maltose system, underlies MalY-dependent repression of the maltose system.

Bacterial Proteins↗

PubMed2000

Benefits of 2.94 micron infrared matrix-assisted laser desorption/ionization for analysis of labile molecules by Fourier transform mass spectrometry.

A 2.94 microm Er:YAG laser was used together with a commercial Fourier transform mass spectrometer to study labile biomolecules. The combination has shown superior performance over conventional 337 nm ultraviolet matrix-assisted laser desorption/ionization (UV-MALDI) Fourier transform mass spectrometry (FTMS), especially for the analysis of peptides with post-translational modifications. With succinic acid as a matrix, the sensitivity of the single-shot analysis was increased by an order of magnitude to the low femtomole level, with significantly less fragmentation observed. Intact molecular ions of a range of O-glycosylated and sulfated peptides were detected. Urea was found to induce even less fragmentation, although at the expense of the total ion yield. Molecular ions of a noncovalent complex (vancomycin + diacetyl-L-Lys-D-Ala-D-Ala) have been observed for the first time in MALDI-FTMS. 2.94 microm infrared (IR) MALDI also produced abundant molecular ions of a range of nonbiological samples, including C60 and C70 fullerenes as well as dimetal coordination complexes.

Calibration↗

PubMed2000

Hybrid cardiac imaging with MR-CAT scan: a feasibility study.

We demonstrate the feasibility of a new versatile hybrid imaging concept, the combined acquisition technique (CAT), for cardiac imaging. The cardiac CAT approach, which combines new methodology with existing technology, essentially integrates fast low-angle shot (FLASH) and echoplanar imaging (EPI) modules in a sequential fashion, whereby each acquisition module is employed with independently optimized imaging parameters. One important CAT sequence optimization feature is the ability to use different bandwidths for different acquisition modules. Twelve healthy subjects were imaged using three cardiac CAT acquisition strategies: a) CAT was used to reduce breath-hold duration times while maintaining constant spatial resolution; b) CAT was used to increase spatial resolution in a given breath-hold time; and c) single-heart beat CAT imaging was performed. The results obtained demonstrate the feasibility of cardiac imaging using the CAT approach and the potential of this technique to accelerate the imaging process with almost conserved image quality.

Coronary Vessels↗

PubMed2000

Partially parallel imaging with localized sensitivities (PILS).

In this study a novel partially parallel acquisition method is presented, which can be used to accelerate image acquisition using an RF coil array for spatial encoding. In this technique, Parallel Imaging with Localized Sensitivities (PILS), it is assumed that the individual coils in the array have localized sensitivity patterns, in that their sensitivity is restricted to a finite region of space. Within the PILS model, a detailed, highly accurate RF field map is not needed prior to reconstruction. In PILS, each coil in the array is fully characterized by only two parameters: the center of coil's sensitive region in the FOV and the width of the sensitive region around this center. In this study, it is demonstrated that the incorporation of these coil parameters into a localized Fourier transform allows reconstruction of full FOV images in each of the component coils from data sets acquired with a reduced number of phase encoding steps compared to conventional imaging techniques. After the introduction of the PILS technique, primary focus is given to issues related to the practical implementation of PILS, including coil parameter determination and the SNR and artifact power in the resulting images. Finally, in vivo PILS images are shown which demonstrate the utility of the technique.

Algorithms↗

PubMed2000

Three-dimensional (13)C-spectroscopic imaging in the isolated infarcted rat heart.

Acquisition weighted (13)C-spectroscopic imaging with three spatial dimensions is demonstrated in the isolated, perfused rat heart. Experiments were performed at 11.75 T with a home-built double resonant (13)C-(1)H probehead. Three-dimensional chemical shift imaging was used to obtain (1)H-decoupled (13)C-spectra in 96-microl voxels in about 58 min. Acquisition weighting significantly reduced signal contamination and improved image quality, with no penalty in sensitivity. As a first application, infarcted hearts were studied during perfusion with [2-(13)C]-sodium acetate. The extent of the incorporation of the (13)C-label into glutamate allows us to distinguish intact and infarcted myocardium. Chemical shift images show a homogeneous glutamate distribution in intact tissue, but a negligible amount in the infarction scar.

Animals↗

PubMed2000

High-resolution diffusion imaging using a radial turbo-spin-echo sequence: implementation, eddy current compensation, and self-navigation.

This work describes a segmented radial turbo-spin-echo technique (DW-rTSE) for high-resolution multislice diffusion-weighted imaging and quantitative ADC mapping. Diffusion-weighted images with an in-plane resolution of 700 microm and almost free of bulk motion can be obtained in vivo without cardiac gating. However, eddy currents and pulsatile brain motion cause severe artifacts when strong diffusion weighting is applied. This work explains in detail the artifacts in projection reconstruction (PR) imaging arising from eddy currents and describes an effective eddy current compensation based on the adjustment of gradient timing. Application of the diffusion gradients in all three orthogonal directions is possible without degradation of the images due to eddy current artifacts, allowing studies of the diffusional anisotropy. Finally, a self-navigation approach is proposed to reduce residual nonrigid body motion artifacts. Five healthy volunteers were examined to show the feasibility of this method.

Anisotropy↗

PubMed2000

23Na and (1)H NMR microimaging of intact plants.

(23)Na NMR microimaging is described to map, for the first time, the sodium distribution in living plants. As an example, the response of 6-day-old seedlings of Ricinus communis to exposure to sodium chloride concentrations from 5 to 300 mM was observed in vivo using (23)Na as well as (1)H NMR microimaging. Experiments were performed at 11.75 T with a double resonant (23)Na-(1)H probehead. The probehead was homebuilt and equipped with a climate chamber. T(1) and T(2) of (23)Na were measured in the cross section of the hypocotyl. Within 85 min (23)Na images with an in-plane resolution of 156 x 156 micrometer were acquired. With this spatial information, the different types of tissue in the hypocotyl can be discerned. The measurement time appears to be short compared to the time scale of sodium uptake and accumulation in the plant so that the kinetics of salt stress can be followed. In conclusion, (23)Na NMR microimaging promises great potential for physiological studies of the consequences of salt stress on the macroscopic level and thus may become a unique tool for characterizing plants with respect to salt tolerance and salt sensitivity.

Hydrogen↗

PubMed2000

Magnetic resonance imaging of coronary arteries and heart valves in a living mouse: techniques and preliminary results.

New investigations in MRI of a mouse heart showed high-contrast cardiac images and thereby the possibility of doing functional cardiac studies of in vivo mice. But is MRI, in addition, capable of visualizing microstructures such as the coronary arteries and the heart valves of a living mouse? To answer this question, 2D and 3D gradient echo sequences with and without flow compensation were used to image the coronary arteries. To increase signal-to-noise ratio, a birdcage resonator was optimized for mouse heart imaging. Contrast between blood and myocardium was achieved through the inflow effect. A segmented three-dimensional FLASH sequence acquired with a multiple overlap thin slab technique showed the best results. With this technique an isotropic resolution of 100 microm was achieved. The left coronary artery could be visualized up to the apex of the heart. This is demonstrated with short axis views and 3D surface reconstructions of the mouse heart. The four cardiac valves were also visible with the 3D method.

Algorithms↗