bluuebunny/crossref_metadata_2025_split huggingface dataset:
Quantitative magnetic resonance spectroscopy: Semi‐parametric modeling and determination of uncertainties
Authors: Elster Clemens , Schubert Florian , Link Alfred , Walzel Monika , Seifert Frank , Rinneberg Herbert 
Published: May 2005

AbstractA semi‐parametric approach for the quantitative analysis of magnetic resonance (MR) spectra is proposed and an uncertainty analysis is given. Single resonances are described by parametric models or by parametrized in vitro spectra and the baseline is determined nonparametrically by regularization. By viewing baseline estimation in a reproducing kernel Hilbert space, an explicit parametric solution for the baseline is derived. A Bayesian point of view is adopted to derive uncertainties, and the many parameters associated with the baseline solution are treated as nuisance parameters. The derived uncertainties formally reduce to Cramér–Rao lower bounds for the parametric part of the model in the case of a vanishing baseline.The proposed uncertainty calculation was applied to simulated and measured MR spectra and the results were compared to Cramér–Rao lower bounds derived after the nonparametrically estimated baselines were subtracted from the spectra. In particular, for high SNR and strong baseline contributions the proposed procedure yields a more appropriate characterization of the accuracy of parameter estimates than Cramér–Rao lower bounds, which tend to overestimate accuracy. Magn Reson Med 53:1288–1296, 2005. © 2005 Wiley‐Liss, Inc.
Correlation between insulin resistance and intramyocellular lipid levels in rats
Authors: Kuhlmann J. , Neumann‐Haefelin C. , Belz U. , Kramer W. , Juretschke H.‐P. , Herling A. W. 
Published: May 2005

AbstractIncreased intramyocellular lipid (IMCL) content has been proposed as biomarker for insulin resistance (IR). An inverse correlation between IMCL and insulin sensitivity (IS) was found in nonathletic humans, whereas in animal models only a few validation studies have been performed. The aim of this study was to investigate the interrelation between IS indices determined by the glucose clamp technique (glucose disposal (GD), exogenous glucose infusion rates (GIR)) and IMCL content in the tibialis (TIB) and the soleus (SOL) muscle obtained by magnetic resonance spectroscopy in different rat models of IR. Diet‐induced insulin‐resistant Wistar rats as well as genetic disease models (ZDF rats) were used. In both muscles, elevated IMCL correlated with an impaired IS in all models of IR. The correlation of IMCL with both parameters for IS was comparable in TIB and SOL. The best fit between IMCL and IS was obtained using TIB and GIR data (r = −0.69, P < 0.001). Diabetic male ZDF rats exhibited comparatively low IMCL levels due to their catabolic state: exclusion of this group improved r. In summary, IMCL, especially in TIB, is a valid biomarker for IS in various rat models of IR with the advantage of a fast repeatable noninvasive measurement in individual animals. Magn Reson Med 53:1275–1282, 2005. © 2005 Wiley‐Liss, Inc.
Cross‐subject comparison of principal diffusion direction maps
Authors: Schwartzman Armin , Dougherty Robert F. , Taylor Jonathan E. 
Published: May 2005

AbstractDiffusion tensor imaging (DTI) data differ fundamentally from most brain imaging data in that values at each voxel are not scalars but 3 × 3 positive definite matrices also called diffusion tensors. Frequently, investigators simplify the data analysis by reducing the tensor to a scalar, such as fractional anisotropy (FA). New statistical methods are needed for analyzing vector and tensor valued imaging data. A statistical model is proposed for the principal eigenvector of the diffusion tensor based on the bipolar Watson distribution. Methods are presented for computing mean direction and dispersion of a sample of directions and for testing whether two samples of directions (e.g., same voxel across two groups of subjects) have the same mean. False discovery rate theory is used to identify voxels for which the two‐sample test is significant. These methods are illustrated in a DTI data set collected to study reading ability. It is shown that comparison of directions reveals differences in gross anatomic structure that are invisible to FA. Magn Reson Med 53:1423–1431, 2005. © 2005 Wiley‐Liss, Inc.
Noninvasive mapping of regional response to segmental allergen challenge using magnetic resonance imaging and [F‐18]fluorodeoxyglucose positron emission tomography
Authors: Holmes James H. , Sorkness Ronald L. , Meibom Sara K. , Sundaram Senthil K. , Perlman Scott B. , Converse Alexander K. , Pyzalski Robert W. , Hahn Andrew D. , Korosec Frank R. , Grist Thomas M. , Fain Sean B. 
Published: May 2005

AbstractMagnetic resonance (MR) and positron emission tomography (PET) imaging techniques were coregistered to demonstrate regional ventilation and inflammation in the lung for in vivo, noninvasive evaluation of regional lung function associated with allergic inflammation. Four Brown Norway rats were imaged pre‐ and post segmental allergen challenge using respiratory‐gated He‐3 magnetic resonance imaging (MRI) to visualize ventilation, T1‐weighted proton MRI to depict inflammatory infiltrate, and [F‐18]fluorodeoxyglucose‐PET to detect regional glucose metabolism by inflammatory cells. Segmental allergen challenges were delivered and the pre‐ and postchallenge lung as well as the contralateral lung were compared. Coregistration of the imaging results demonstrated that regions of ventilation defects, inflammatory infiltrate, and increased glucose metabolism correlated well with the site of allergen challenge delivery and inflammatory cell recruitment, as confirmed by histology. This method demonstrates that fusion of functional and anatomic PET and MRI image data may be useful to elucidate the functional correlates of inflammatory processes in the lungs. Magn Reson Med 53:1243–1250, 2005. © 2005 Wiley‐Liss, Inc.
Focused, eight‐element transceive phased array coil for parallel magnetic resonance imaging of the chest—Theoretical considerations
Authors: Keong Li Bing , Liu Feng , Crozier Stuart 
Published: May 2005

AbstractA new transceive system for chest imaging for MRI applications is presented. A focused, eight‐element transceive torso phased array coil is designed to investigate transmitting a focused radiofrequency field deep within the torso and to enhance signal homogeneity in the heart region. The system is used in conjunction with the SENSE reconstruction technique to enable focused parallel imaging. A hybrid finite‐difference‐time‐domain/method‐of‐moments method is used to accurately predict the radiofrequency behavior inside the human torso. The simulation results reported herein demonstrate the feasibility of the design concept, which shows that radiofrequency field focusing with SENSE reconstruction is theoretically achievable. Magn Reson Med 53:1251–1257, 2005. © 2005 Wiley‐Liss, Inc.
Functional magnetic resonance imaging with intermolecular double‐quantum coherences at 3 T
Authors: Schäfer Andreas , Jochimsen Thies H. , Möller Harald E. 
Published: May 2005

AbstractFunctional magnetic resonance imaging (fMRI) based on the selection of intermolecular double‐quantum coherences (iDQC) was performed with a standard birdcage coil at 3 T in a group of normal human volunteers. Suppression of spurious signal contributions from unwanted coherence‐transfer pathways was achieved by combining a two‐step phase cycle and a long repetition time of 5 s. A gradient‐recalled echo iDQC sequence (echo time, TE = 80 ms) yielded robust activation with a visual paradigm. Maximum z‐scores were about half of those observed with conventional blood‐oxygen level dependent fMRI, whereas the functional signal change increased by more than a factor of 5. No activation was obtained with a spin‐echo iDQC sequence (TE = 160 ms), in which dephasing accumulated during the evolution period was fully rephased by an appropriate delay time. It is hypothesized that substantial inherent diffusion weighting of the iDQC technique efficiently suppresses intravascular contributions to the functional contrast. A consistent quantitative explanation of the observed amount of signal change currently remains speculative. Magn Reson Med 53:1402–1408, 2005. © 2005 Wiley‐Liss, Inc.
Theoretical and experimental evaluation of broadband decoupling techniques for in vivo nuclear magnetic resonance spectroscopy
Authors: de Graaf Robin A. 
Published: May 2005

AbstractA theoretical and experimental evaluation of existing broadband decoupling methods with respect to their utility for in vivo 1H‐13C NMR spectroscopy is presented. Simulations are based on a modified product operator formalism, while an experimental evaluation is performed on in vitro samples and human leg and rat brain in vivo. The performance of broadband decoupling methods was evaluated with respect to the required peak and average RF powers, decoupling bandwidth, decoupling side bands, heteronuclear scalar coupling constant, and sensitivity toward B2 inhomogeneity. In human applications only the WALTZ and MLEV decoupling methods provide adequate decoupling performance at RF power levels that satisfy the FDA guidelines on local tissue heating. For very low RF power levels (B2max < 300 Hz) one should verify empirically whether the experiment will benefit from broadband decoupling. At higher RF power levels acceptable for animal studies additional decoupling techniques become available and provide superior performance. Since the average RF power of adiabatic RF pulses is almost always significantly lower than the peak RF power, it can be stated that for average RF powers suitable for animal studies it is always possible to design an adiabatic decoupling scheme that outperforms all other schemes. B2 inhomogeneity degrades the decoupling performance of all methods, but the decoupling bandwidths for WALTZ‐16 and especially adiabatic methods are still satisfactory for useful in vivo decoupling with a surface coil. Magn Reson Med 53:1297–1306, 2005. © 2005 Wiley‐Liss, Inc.
Diffusional kurtosis imaging: The quantification of non‐gaussian water diffusion by means of magnetic resonance imaging
Authors: Jensen Jens H. , Helpern Joseph A. , Ramani Anita , Lu Hanzhang , Kaczynski Kyle 
Published: May 2005

AbstractA magnetic resonance imaging method is presented for quantifying the degree to which water diffusion in biologic tissues is non‐Gaussian. Since tissue structure is responsible for the deviation of water diffusion from the Gaussian behavior typically observed in homogeneous solutions, this method provides a specific measure of tissue structure, such as cellular compartments and membranes. The method is an extension of conventional diffusion‐weighted imaging that requires the use of somewhat higher b values and a modified image postprocessing procedure. In addition to the diffusion coefficient, the method provides an estimate for the excess kurtosis of the diffusion displacement probability distribution, which is a dimensionless metric of the departure from a Gaussian form. From the study of six healthy adult subjects, the excess diffusional kurtosis is found to be significantly higher in white matter than in gray matter, reflecting the structural differences between these two types of cerebral tissues. Diffusional kurtosis imaging is related to q‐space imaging methods, but is less demanding in terms of imaging time, hardware requirements, and postprocessing effort. It may be useful for assessing tissue structure abnormalities associated with a variety of neuropathologies. Magn Reson Med 53:1432–1440, 2005. © 2005 Wiley‐Liss, Inc.
Quantification of glycine and taurine conjugated bile acids in human bile using 1H NMR spectroscopy
Authors: Ijare Omkar B. , Somashekar B. S. , Gowda G. A. Nagana , Sharma Ajay , Kapoor V. K. , Khetrapal C. L. 
Published: May 2005

AbstractA simple method for quantification of conjugated bile acids in human bile using 1H NMR spectroscopy is presented. Bile acids in human bile are essentially conjugated with either glycine or taurine. The amide NH resonances from the conjugated bile acids are invariably devoid of interfering signals in 1H NMR spectra. Under physiologic conditions of human bile (pH ∼7.0 to 7.7), amide signal intensities are attenuated due to the chemical exchange and hence quantitative estimation is precluded. In the present study, the quantity of total glycine and taurine conjugated bile acids could be obtained accurately by suppressing the amide exchange by reducing the pH slightly lower than physiologic value (6.0 ± 0.5). Further, the quantity of glycine conjugated bile acids can be calculated accurately by subtracting the quantity of taurine conjugated bile acids from the total conjugated bile acids as determined from the present method. Magn Reson Med 53:1441–1446, 2005. © 2005 Wiley‐Liss, Inc.
Quantitative assessment of emphysema using hyperpolarized 3He magnetic resonance imaging
Authors: Spector Z. Z. , Emami K. , Fischer M. C. , Zhu J. , Ishii M. , Vahdat V. , Yu J. , Kadlecek S. , Driehuys B. , Lipson D. A. , Gefter W. , Shrager J. , Rizi R. R. 
Published: May 2005

AbstractIn this experiment, Sprague–Dawley rats with elastase‐induced emphysema were imaged using hyperpolarized 3He MRI. Regional fractional ventilation r, the fraction of gas replaced with a single tidal breath, was calculated from a series of images in a wash‐in study of hyperpolarized gas. We compared the regional fractional ventilation in these emphysematous rats to the regional fractional ventilations we calculated from a previous baseline study in healthy Sprague–Dawley rats. We found that there were differences in the maps of fractional ventilation and its associated frequency distribution between the healthy and emphysematous rat lungs. Fractional ventilation tended to be much lower in emphysematous rats than in normal rats. With this information, we can use data on fractional ventilation to regionally distinguish between healthy and emphysematous portions of the lung. The successful implementation of such a technique on a rat model could lead to work toward the future implementation of this technique in human patients. Magn Reson Med 53:1341–1346, 2005. © 2005 Wiley‐Liss, Inc.
Enhanced viability imaging: Improved contrast in myocardial delayed enhancement using dual inversion time subtraction
Authors: Foo Thomas K. F. , Wolff Steven D. , Gupta Sandeep N. , Kraitchman Dara L. 
Published: May 2005

AbstractIn delayed contrast‐enhanced MRI for the assessment of myocardial viability, the TI time in a gated inversion‐recovery segmented gradient echo sequence is usually selected to null signal from normal myocardium. Although this TI time generates good contrast between the enhancing infarcted tissue and normal myocardium, there is usually less contrast between the infarct and the blood pool. A subtractive technique utilizing two acquisitions at a long and short TI time is proposed to improve the delineation between infarct‐blood and infarct‐myocardium. The concept was demonstrated in six mongrel dogs with reperfused myocardial infarction. Infarct‐normal myocardium contrast (signal difference) using the proposed enhanced viability imaging (ENVI) technique was 142 ± 50% (P < 0.001) that of standard magnitude inversion recovery (IR), while at the same TI time for the primary image, infarct‐blood contrast, was 247 ± 136% (P < 0.002) that of magnitude IR. Accounting for increased noise due to the subtraction, signal difference‐to‐noise ratios (SDNR) did not show a significant change for infarct‐myocardium but infarct‐blood SDNR for ENVI was 174 ± 105% that of magnitude‐IR (P < 0.03). Thus, marked improvement in the delineation of the infarcted zone was noted over a range of TI times. Magn Reson Med 53:1484–1489, 2005. © 2005 Wiley‐Liss, Inc.
Minimal feedback vertex sets in directed split‐stars
Authors: Wang Fu‐Hsing , Hsu Cheng‐Ju , Tsai Jen‐Chih 
Published: May 2005

AbstractIn a graph G = (V,E), a subset F ⊂ V(G) is a feedback vertex set of G if the subgraph induced by V(G)\F is acyclic. In this article, we propose an algorithm for finding minimal feedback vertex sets of directed split‐stars. Indeed, our algorithm can derive an upper bound on the size of the minimum feedback vertex set in directed split‐stars. Moreover, a simple distributed algorithm is presented for obtaining such sets. © 2005 Wiley Periodicals, Inc. NETWORKS, Vol. 45(4), 218–223 2005
Optimal broadcasting with universal lists based on competitive analysis*
Authors: Kim Jae‐Hoon , Chwa Kyung‐Yong 
Published: May 2005

AbstractIn this article we study a variant of broadcasting: each node has a predetermined ordered list of neighbors regardless of the node, called the source, from which the originating message is transmitted to all nodes in a network. Each node transmits a received message to its neighbors in order of the list. We propose a new measure of the efficiency of a Broadcasting scheme, which is obtained from competitive analysis, and we design new broadcasting schemes for lines, completek‐ary trees, grids, complete graphs, and hypercubes. In particular, we provide optimal broadcasting schemes for lines and grids. © 2005 Wiley Periodicals, Inc. NETWORKS, Vol. 45(4), 224–231 2005
Lowering eccentricity of a tree by node upgrading
Authors: Ibaraki Toshihide , Vaxès Yann , Yang Xiao‐guang 
Published: May 2005

AbstractThe eccentricity lowering problem is to reduce the eccentricity of a network by upgrading some nodes (that is, shrinking the lengths of the edges incident to such nodes). We consider two types of node‐upgrading strategies, that is, a continuous upgrading strategy and a discrete upgrading strategy, where the improvement under the first strategy is a continuous variable, and the improvement under the second strategy is a fixed amount. These problems are hard even to approximate, for general graphs. Therefore, we restrict our attention to graphs with simple structures. Assuming that the graph G = (V,E) is a tree, we show that the eccentricity lowering problem under the continuous node‐upgrading strategy can be reduced to the eccentricity lowering problem under the continuous edge‐upgrading strategy, and can be solved by an O(|V| log |V|) time algorithm. We also show that the problem for a tree is NP‐hard under the discrete upgrading strategy, but admits a fully polynomial approximation scheme, if the graph is a line. © 2005 Wiley Periodicals, Inc. NETWORKS, Vol. 45(4), 232–239 2005
Up‐regulation of gene expression by hypoxia is mediated predominantly by hypoxia‐inducible factor 1 (HIF‐1)
Authors: Greijer AE , van der Groep P , Kemming D , Shvarts A , Semenza GL , Meijer GA , van de Wiel MA , Belien JAM , van Diest PJ , van der Wall E 
Published: May 2005

AbstractThe hypoxia‐inducible factor 1 (HIF‐1) plays a critical role in cellular responses to hypoxia. The aim of the present study was to evaluate which genes are induced by hypoxia, and whether this induction is mediated by HIF‐1, by expression microarray analysis of wt and HIF‐1α null mouse fibroblasts. Forty‐five genes were up‐regulated by hypoxia and 40 (89%) of these were regulated by HIF‐1. Of the 114 genes down‐regulated by hypoxia, 19 (17%) were HIF‐1‐dependent. All glycolytic enzymes were strongly up‐regulated by hypoxia in a HIF‐1‐dependent manner. Genes already known to be related to hypoxia, such as glucose transporter 1, BNIP3, and hypoxia‐induced gene 1, were induced. In addition, multiple new HIF‐1‐regulated genes were identified, including genes involved in metabolism (adenylate kinase 4, galactokinase), apoptosis (galectin‐3 and gelsolin), and invasion (RhoA). Genes down‐regulated by hypoxia were involved in cytoskeleton maintenance (Rho kinase), mRNA processing (heterogeneous nuclear ribonucleoprotein H1 and splicing factor), and DNA repair (REV3). Furthermore, seven cDNAs from genes with unknown function or expressed sequence tags (ESTs) were up‐regulated and 27 such cDNAs were down‐regulated. In conclusion, hypoxia causes down‐ rather than up‐regulation of gene expression and HIF‐1 seems to play a major role in the regulation of hypoxia‐induced genes. Copyright © 2005 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
Effect of dissociation of iron–boron pairs in crystalline silicon on solar cell properties
Authors: Schmidt Jan 
Published: May 2005

AbstractThe effect of dissociation of interstitial iron‐substitutional boron (FeiBs) pairs, as it occurs under illumination in iron‐contaminated silicon solar cells, on the solar cell properties has been studied on the basis of numerical device simulations using reported recombination parameters for Fei and FeiBs. Most cell parameters are found to degrade during FeiBs dissociation. However, the open‐circuit voltage can also increase within certain ranges of the iron concentration. Critical iron concentrations are determined, giving the threshold contamination level above which a significant degradation in the corresponding cell parameter can be observed. The threshold iron contamination level of the open‐circuit voltage degradation is found to be up to two orders of magnitude larger than the threshold iron level of the short‐circuit current degradation. As the behaviour of the cell parameters under illumination is specific to the dissociation of FeiBs pairs, the characteristic changes in the cell parameters due to illumination may be used as a simple way of identifying iron contamination problems in silicon solar cells. Copyright © 2005 John Wiley & Sons, Ltd.
Protein microarrays for antibody profiling: Specificity and affinity determination on a chip
Authors: Poetz Oliver , Ostendorp Ralf , Brocks Bodo , Schwenk Jochen M. , Stoll Dieter , Joos Thomas O. , Templin Markus F. 
Published: May 2005

AbstractProtein microarray technology facilitates the detection and quantification of hundreds of binding reactions in one reaction from a minute amount of sample. Proof‐of‐concept studies have shown that the set‐up of sensitive assay systems based on protein arrays is possible, however, the lack of specific capture reagents limits their use. Therefore, the generation and characterisation of capture molecules is one of the key topics for the development of protein array based systems. Recombinant antibody technologies, such as HuCAL® (human combinatorial antibody library; MorphoSys, Munich, Germany), allow the fast generation of highly specific binders to nearly any given target molecule. Although antibody libraries comprise billions of members, it is not the selection process, but the detailed characterisation of the pre‐selected monoclonal antibodies that presents the bottleneck for the production of high numbers of specific binders. In order to obtain detailed information on the properties of such antibodies, a microarray‐based method has been developed. We show that it is possible to define the specificity of recombinant Fab fragments by protein and peptide microarrays and that antibodies can be classified by binding patterns. Since the assay uses a miniaturised system for the detection of antibody‐antigen interactions, the observed binding occurs under ambient analyte conditions as defined by Ekins (J. Pharm. Biomed. Anal. 1989, 7, 155–168). This allows the determination of a relative affinity value for each binding event, and a ranking according to affinity is possible. The new microarray based approach has an extraordinary potential to speed up the screening process for the generation of recombinant antibodies with pre‐defined selection criteria, since it is intrinsically a high‐throughput technology.