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R de Beer

Publications and source records attributed to R de Beer.

At least 19 recordsLinked to original sources
PubMed2001

Java-based graphical user interface for the MRUI quantitation package.

This article describes the Java-based version of the magnetic resonance user interface (MRUI) quantitation package. This package allows MR spectroscopists to easily perform time-domain analysis of in vivo MR spectroscopy data. We show that the Java programming language is very well suited for developing highly interactive graphical software applications such as the MRUI software. We have also established that MR quantitation algorithms, programmed in other languages, can easily be embedded into the Java-based MRUI by using the Java native interface (JNI). This new graphical user interface (GUI) has been conceived for the processing of large data sets and uses prior knowledge data-bases to make interactive quantitation algorithms more userfriendly.

Algorithms↗
PubMed2001

Java-based graphical user interface for MRUI, a software package for quantitation of in vivo/medical magnetic resonance spectroscopy signals.

This article describes a Java-based graphical user interface for the magnetic resonance user interface (MRUI) quantitation package. This package allows MR spectroscopists to easily perform time-domain analysis of in vivo/medical MR spectroscopy data. We have found that the Java programming language is very well suited for developing highly interactive graphical software applications such as the MRUI system. We also have established that MR quantitation algorithms, programmed in the past in other languages, can easily be embedded into the Java-based MRUI by using the Java native interface (JNI).

Algorithms↗
PubMed1998

The viral spike protein is not involved in the polarized sorting of coronaviruses in epithelial cells.

Coronaviruses are assembled by budding into a pre-Golgi compartment from which they are transported along the secretory pathway to leave the cell. In cultured epithelial cells, they are released in a polarized fashion; depending on the virus and cell type, they are sorted preferentially either to the apical domain or to the basolateral plasma membrane domain. In this study, we investigated the role of the coronavirus spike protein, because of its prominent position in the virion the prime sorting candidate, in the directionality of virus release. Three independent approaches were taken. (i) The inhibition of N glycosylation by tunicamycin resulted in the synthesis of spikeless virions. The absence of spikes, however, did not influence the polarity in the release of virions. Thus, murine hepatitis virus strain A59 (MHV-A59) was still secreted from the basolateral membranes of mTAL and LMR cells and from the apical sides of MDCK(MHVR) cells, whereas transmissible gastroenteritis virus (TGEV) was still released from the apical surfaces of LMR cells. (ii) Spikeless virions were also studied by using the MHV-A59 temperature-sensitive mutant Albany 18. When these virions were produced in infected LMR and MDCK(MHVR) cells at the nonpermissive temperature, they were again preferentially released from basolateral and apical membranes, respectively. (iii) We recently demonstrated that coronavirus-like particles resembling normal virions were assembled and released when the envelope proteins M and E were coexpressed in cells (H. Vennema, G.-J. Godeke, J. W. A. Rossen, W. F. Voorhout, M. C. Horzinek, D.-J. E. Opstelten, and P. J. M. Rottier, EMBO J. 15:2020-2028, 1996). The spikeless particles produced in mTAL cells by using recombinant Semliki Forest viruses to express these two genes of MHV-A59 were specifically released from basolateral membranes, i.e., with the same polarity as that of wild-type MHV-A59. Our results thus consistently demonstrate that the spike protein is not involved in the directional sorting of coronaviruses in epithelial cells. In addition, our observations with tunicamycin show that contrary to the results with some secretory proteins, the N-linked oligosaccharides present on the viral M proteins of coronaviruses such as TGEV also play no role in viral sorting. The implications of these conclusions are discussed.

Animals↗
PubMed1995

The outcome of babies of mothers with severe rhesus incompatibility treated at Tygerberg Hospital, 1980-1993.

OBJECTIVE: To determine the outcome of babies of mothers with severe rhesus (Rh) incompatibility treated by elective delivery when the amniotic optical density at 450 nm crossed Whitfield's action line (group 1), by plasmapheresis and immunotherapy (group 2) or by means of intra-uterine intravascular transfusions (group 3). STUDY DESIGN: A retrospective study of 55 mothers and their 57 fetuses with severe Rh incompatibility at < 34 weeks' pregnancy duration. MAIN OUTCOME PARAMETERS: Number of mothers in each treatment group, prevalence of intra-uterine death, hydrops, intra-uterine intravascular transfusions, cord haematocrit, cord bilirubin, number of liveborn babies, birth weight, neonatal death, hyaline membrane disease (HMD) and exchange transfusions. STUDY POPULATION AND SETTING: All mothers and babies with severe Rh incompatibility (defined as an amniotic optical density of 450 nm in the upper and upper-mid zone on the Liley chart at < 34 weeks' pregnancy duration, previous fetal hydrops or Rh-related intra-uterine death (IUD), fetal hydrops on ultrasound or a fetal haematocrit < 30% at cordocentesis) treated at Tygerberg Hospital between January 1980 and January 1993. There were 20 fetuses each in groups 1 and 3, and 17 in group 2. RESULTS: A total of 48 babies (84%) were liveborn and of these 74% survived the neonatal period. (ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Saturation correction in human cardiac 31P MR spectroscopy at 1.5 T.

This study was conducted to verify the validity of using saturation factors obtained from unlocalized 31P spectra containing both chest wall and heart muscle signals for correcting human heart muscle phosphocreatine/beta-adenosine triphosphate (PCr/beta-ATP) ratios. Saturation factors and T1 relaxation times were determined from 31P magnetic resonance spectra of human chest wall and heart muscle simultaneously in healthy volunteers using one-dimensional spectroscopic imaging in combination with a two-dimensional ISIS sequence by using adiabatic 180 degrees inversion and adiabatic 90 degrees excitation pulses at 1.5 T. Blood corrected saturation factors for PCr/beta-ATP at a TR of 2.4 s were significantly different in heart muscle and chest wall muscle, 1.30 +/- 0.25 and 1.73 +/- 0.31, respectively (p < 0.05). T1 values for PCr and beta-ATP in heart muscle were 4.28 +/- 0.72 and 2.99 +/- 0.52 and in chest wall muscle 6.82 +/- 1.07 and 3.39 +/- 0.48, respectively. The T1(PCr)/T1(beta-ATP) ratios in chest wall and heart muscle were not identical. The mean PCr/beta-ATP ratios in heart and chest wall muscle of six healthy volunteers were 1.23 +/- 0.17 and 3.71 +/- 0.53, respectively.

Adenosine Triphosphate↗
PubMed1993

Post-ischemic contractile dysfunction does not correlate with an elevated intracellular free [Mg2+]: a 31P-NMR study on isolated rat and rabbit hearts.

The aim of this study was to investigate whether intracellular free Mg2+ (Mgr), which increases during myocardial ischemia due to hydrolysis of ATP, remained elevated during reperfusion after a relatively short period of ischemia and thereby could account for temporary post-ischemic contractile dysfunction, often referred to as stunning. 31P-magnetic resonance (31P-NMR) spectroscopy was used to follow creatine phosphate, adenosine triphosphate, intracellular inorganic phosphate, intracellular pH and Mgr simultaneously with left ventricular developed pressure (LVDP) and coronary flow in isolated rat and rabbit hearts, which were perfused (37 degrees C) according to Langndorff. LVDP was measured in an isovolumic way by means of an intraventricular latex balloon. Rat hearts (300 beats/min) were made globally ischemic for 15 min and rabbit hearts (180 beats/min) for 15 or 20 min. All hearts were reperfused for 60 min. Control hearts were perfused for 75 min without being made ischemic. During ischemia Mgr (mmol/l) increased from 0.76 +/- 0.20 to 4.34 +2- 1.99 in the rat hearts, and from 0.72 +/- 0.22 to 2.18 +/- 1.06 (15 min) and 2.35 +/- 1.26 (20 min) in the rabbit hearts. During reperfusion Mgr in the three groups returned to the level of the control hearts within 7.5 min, and LVDP within 25 min. At the end of the reperfusion period ATP content amounted to 56 +/- 17% (rat hearts), 66 +/- 10% (rabbit hearts; 15 min ischemia group) and 61 +/- 7% (rabbit hearts; 20 min ischemia group) of the pre-ischemic levels. The results confirm that in vitro stunning is a short-lived phenomenon and indicate that an increased Mgr is not involved in this temporary mechanical dysfunction.

Adenosine Triphosphate↗
PubMed1993

Reduced lipid contamination in in vivo 1H MRSI using time-domain fitting and neural network classification.

It is a well-known problem that metabolite maps, reconstructed from in vivo 1H MRSI data sets, may suffer from contamination caused by the presence of strong lipid signals. In the present investigation, the lipid problem was addressed by applying specific signal processing and data-analysis techniques, combined with pattern recognition based on the concept of the artificial neural network. In order to arrive at images, cleaned from lipid artifacts, we have applied our previously introduced iterative and noniterative time-domain fitting procedures. Furthermore, reduction in computational time of the image reconstructions could be realized by using information provided by a neural network classification of the spectra, calculated from the MRSI data sets.

Artifacts↗
PubMed1991

Neurotensin, vaso-active intestinal polypeptide and gastrin levels in plasma and portal venous blood in experimental mesenteric ischaemia.

The effect of mesenteric ischaemia on the levels of neurotensin, vaso-active intestinal polypeptide and gastrin in portal venous blood and in the peripheral circulation was studied in two groups of 7 and 6 baboons (Papio ursinus). In peripheral blood a decreasing trend in levels of neurotensin was observed, while vaso-active intestinal polypeptide and gastrin levels were unchanged. There was a similar trend in neurotensin levels in portal venous blood, together with an increasing trend in levels of vaso-active intestinal polypeptide. Gastrin levels were unchanged. Further investigation of these apparent trends in a large number of animals is warranted.

Animals↗
PubMed1989

1H image-guided localized 31P MR spectroscopy of human brain: quantitative analysis of 31P MR spectra measured on volunteers and on intracranial tumor patients.

1H image-guided 31P MR spectra of normal human brain and of intracranial tumors have been analyzed quantitatively. Tumor types examined include prolactinoma, lymphoma, and various grade gliomas. The experimental signals were processed by means of a time-domain least-square fitting procedure, which yields the spectral parameters, as well as a prediction of the standard deviations. Significant spectral variations are observed within both populations of normal brain and of intracranial tumor 31P MR spectra. The metabolic ratios derived from the glioma 31P MR spectra and from corresponding uninfiltrated brain tissue do not differ significantly. Significant differences are, however, observed between the metabolic ratios of prolactinoma and uninfiltrated tissue 31P MR spectra. Alkaline pH values are found for the prolactinoma and the high-grade gliomas. Furthermore, spectral differences are observed between the patient's uninfiltrated tissue 31P MR spectra and those of an unmatched population of volunteers. This underscores the necessity for control measurements on the uninfiltrated tissue of the patient and for controls from a matched population of healthy individuals.

Adult↗
PubMed1988

In vivo 31P NMR spectroscopy of the rat cerebral cortex during acute hepatic encephalopathy.

During the development of acute hepatic encephalopathy, induced by acute liver ischemia, changes in brain 31P NMR spectra and EEG spectra were studied over 8:45 h in eight rats. At the end of this period the brain amino acid concentrations were determined. The results were compared with the same measurements in four normal and three portacaval shunted rats. Signs of acute HE, as judged by the EEG left index, started 5 h after the induction of acute liver ischemia. No accompanying significant changes in the cortical relative phosphocreatine and ATP concentration and intracellular pH were observed. The cortical relative Pi concentration had only slightly increased at t = 8 h. The concentrations of almost all measured brain amino acids, especially glutamine had increased at t = 8:45 h. At t = 8 h, rats with very severe HE had a small, but significant decrease of brain ATP concentrations. Their brain amino acid concentrations were more disturbed than in rats with less severe HE. It is concluded that a change in the cortical cerebral energy rich phosphate concentration is not an important pathophysiological mechanism during the development of acute HE. The observed changes in brain amino acids concentrations could be either part of a multifactorial pathogenesis or could be epiphenomena.

Adenosine Triphosphate↗
PubMed1985

Application of linear prediction and singular value decomposition (LPSVD) to determine NMR frequencies and intensities from the FID.

A parametric spectral analysis based on linear prediction and singular value decomposition has been applied to the 31P FID of a tumor implanted in a mouse. It is found that a number of complications that may arise in in vivo FFT NMR can be circumvented. The new method yields all parameters of the spectral components, i.e., the frequency, amplitude, damping constant, and phase.

Animals↗
PubMed1980

The prosthetic group of methylamine dehydrogenase from Pseudomonas AM1: evidence for a quinone structure.

The g-value and linewidth of ESR spectra of methylamine dehydrogenase (primary-amine:(acceptor) oxidoreductase (deaminating) EC 1.4.99.-) and methanol dehydrogenase (alcohol:(acceptor) oxidoreductase, EC 1.1.99.8) are very similar. This similarity is also reflected in electron-nuclear double resonance (ENDOR) results, the coupling constants of two protons in one enzyme equalling those in the other. The presence of a third proton in the ENDOR spectrum of methylamine dehydrogenase suggests a different structure or a different kind of interaction which can be related to the finding that the resolved ROSTHETIC GROUP IS PROTEIN-BOUND. The bound prosthetic group has a high redox-potential, supporting the conclusion from the ESR and ENDOR results that it is a quinone derivative.

Electron Spin Resonance Spectroscopy↗
PubMedDate not supplied

Application of time-domain fitting in the quantification of in vivo 1H spectroscopic imaging data sets.

Time-domain model function fitting techniques were applied to improve the reconstruction of metabolite maps from the data sets obtained from in vivo 1H spectroscopic imaging (SI) experiments. First, residual water-related signals were removed from the SI data sets by using SVD-based linear time-domain fitting based upon the HSVD (State Space) approach. Second, peak integrals of the metabolites of interest were obtained by quantifying the proton spin-echoes of the voxels by means of non-linear time-domain fitting based upon the maximum likelihood principle. Third, in order to save computational time, interpolation of the metabolite images (from size 32 x 32 to 128 x 128) was performed in the image-domain by applying one-dimensional cubic splines. It was found that the residual water signals can be almost completely removed from the SI data sets by applying the linear HSVD fitting method. Furthermore, it was found that voxel dependency of certain NMR parameters (e.g., variations of the spin-echo offset frequencies and/or phase factors) can be accounted for automatically by applying the nonlinear time-domain fitting technique. For that purpose it appeared to be essential to employ prior knowledge of the NMR spectral parameters.

Aspartic Acid↗