bluuebunny/crossref_metadata_2025_split huggingface dataset:
View‐ordering in radial fast spin‐echo imaging
Authors: Theilmann Rebecca J. , Gmitro Arthur F. , Altbach Maria I. , Trouard Theodore P. 
Published: March 2004

AbstractRadial MRI sequences are frequently used to obtain images with reduced sensitivity to motion. To decrease imaging time, multiple spin‐echo acquisitions can be incorporated into radial sequences. In this case, different radial lines of Fourier data have different TE times and the resulting images can contain streaking artifacts due to T2 decay. The streaking is not only dependent on the T2 of the object and the timing of the data acquisition, but also on the order in which radial lines are collected (view order). The view ordering can easily be controlled to minimize artifacts due to T2 decay as well as motion. Four view‐ordering techniques are presented and evaluated for the radial FSE sequence. Magn Reson Med 51:768–774, 2004. © 2004 Wiley‐Liss, Inc.
The effect of gradient sampling schemes on measures derived from diffusion tensor MRI: A Monte Carlo study†
Authors: Jones Derek K. 
Published: March 2004

AbstractThere are conflicting opinions in the literature as to whether it is more beneficial to use a large number of gradient sampling orientations in diffusion tensor MRI (DT‐MRI) experiments than to use a smaller number of carefully chosen orientations. In this study, Monte Carlo simulations were used to study the effect of using different gradient sampling schemes on estimates of tensor‐derived quantities assuming a b‐value of 1000 smm–2. The study focused in particular on the effect that the number of unique gradient orientations has on uncertainty in estimates of tensor‐orientation, and on estimates of the trace and anisotropy of the diffusion tensor. The results challenge the recently proposed notion that a set of six icosahedrally‐arranged orientations is optimal for DT‐MRI. It is shown that at least 20 unique sampling orientations are necessary for a robust estimation of anisotropy, whereas at least 30 unique sampling orientations are required for a robust estimation of tensor‐orientation and mean diffusivity. Finally, the performance of sampling schemes that use low numbers of sampling orientations, but make efficient use of available gradient power, are compared to less efficient schemes with larger numbers of sampling orientations, and the relevant scenarios in which each type of scheme should be used are discussed. Magn Reson Med 51:807–815, 2004. Published 2004 Wiley‐Liss, Inc.
Resolution‐insensitive velocity and flow rate measurement in low‐background phase‐contrast MRA
Authors: van der Weide Remko , Viergever Max A. , Bakker Chris J. G. 
Published: March 2004

AbstractMagnetic resonance (MR) phase‐contrast (PC) flow measurements are degraded by partial volume errors when the spatial resolution is low, in particular when a large difference in signal magnitude exists between the fluid and the surrounding material. The latter is often the case in phantom studies and may be encountered when flow is measured in prosthetic vessel segments (such as shunts, grafts, and bypasses) and in contrast‐enhanced blood. This paper presents a new method that is designed to measure flow in vessels of circular cross‐section with Poiseuille flow and negligible background signal arising from static material around the lumen. The method calculates the average flow velocity directly from the original complex image data by integrating the signal in oppositely velocity‐sensitized PC images. The radius is calculated from the summed signal modulus. The method allows accurate and resolution‐insensitive measurements of the average flow velocity to be obtained in both cross‐sectional and in‐plane acquisitions. It is not critical to any of the assumed conditions. The validity and capabilities of the proposed technique are demonstrated by in vitro experiments. Magn Reson Med 51:785–793, 2004. © 2004 Wiley‐Liss, Inc.
MRI assessment of neuropathology in a transgenic mouse model of Alzheimer's disease
Authors: Helpern Joseph A. , Lee Sang‐Pil , Falangola Maria F. , Dyakin Victor V. , Bogart Adam , Ardekani Babak , Duff Karen , Branch Craig , Wisniewski Thomas , de Leon Mony J. , Wolf Oliver , O'Shea Jacqueline , Nixon Ralph A. 
Published: March 2004

AbstractThe cerebral deposition of amyloid β‐peptide, a central event in Alzheimer's disease (AD) pathogenesis, begins several years before the onset of clinical symptoms. Noninvasive detection of AD pathology at this initial stage would facilitate intervention and enhance treatment success. In this study, high‐field MRI was used to detect changes in regional brain MR relaxation times in three types of mice: 1) transgenic mice (PS/APP) carrying both mutant genes for amyloid precursor protein (APP) and presenilin (PS), which have high levels and clear accumulation of β‐amyloid in several brain regions, starting from 10 weeks of age; 2) transgenic mice (PS) carrying only a mutant gene for presenilin (PS), which show subtly elevated levels of Aβ‐peptide without β‐amyloid deposition; and 3) nontransgenic (NTg) littermates as controls. The transverse relaxation time T2, an intrinsic MR parameter thought to reflect impaired cell physiology, was significantly reduced in the hippocampus, cingulate, and retrosplenial cortex, but not the corpus callosum, of PS‐APP mice compared to NTg. No differences in T1 values or proton density were detected between any groups of mice. These results indicate that T2 may be a sensitive marker of abnormalities in this transgenic mouse model of AD. Magn Reson Med 51:794–798, 2004. © 2004 Wiley‐Liss, Inc.
Assessment of myocardial infarction in pigs using a rapid clearance blood pool contrast medium
Authors: Dewey Marc , Kaufels Nicola , Laule Michael , Schnorr Jörg , Wagner Susanne , Kivelitz Dietmar , Raynaud Jean‐Sébastien , Robert Philippe , Hamm Bernd , Taupitz Matthias 
Published: March 2004

AbstractDelayed enhancement MRI using extracellular contrast media allows reliable detection of myocardial infarction. If blood pool contrast media like P792 (Vistarem, Guerbet, France), in addition to improving coronary MR angiography, can be shown to also produce delayed enhancement in myocardial infarction they could improve the prerequisites for a comprehensive cardiac MR examination. In this study reperfused myocardial infarction in five minipigs was imaged with an inversion‐recovery fast low‐angle shot sequence using P792 (0.013 mmol Gd/kg) and the extracellular contrast medium Gd‐DOTA (Dotarem, 0.1 mmol Gd/kg, Guerbet). The infarction size determined on MRI using P792 (7.55 ± 2.31 cm2) highly correlated both with histomorphometry (7.81 ± 2.18 cm2, r = 0.991, P < 0.002) and with MRI using Gd‐DOTA (7.85 ± 2.35 cm2, r = 0.978, P < 0.005). Bland‐Altman analysis showed that the limit of agreement of MRI using P792 compared to histomorphometry was 3.3 ± 7.6% of the infarction size. The contrast‐to‐noise ratio between infarcted and remote myocardium was not significantly different between Gd‐DOTA (5.9 ± 2.4) and P792 (4.4 ± 1.1, P = 0.5). The blood pool contrast medium P792 allows reliable assessment of viability with good contrast and accuracy. Magn Reson Med 51:703–709, 2004. © 2004 Wiley‐Liss, Inc.
Active device tracking and high‐resolution intravascular MRI using a novel catheter‐based, opposed‐solenoid phased array coil
Authors: Hillenbrand Claudia M. , Elgort Daniel R. , Wong Eddy Y. , Reykowski Arne , Wacker Frank K. , Lewin Jonathan S. , Duerk Jeffrey L. 
Published: March 2004

AbstractA novel two‐element, catheter‐based phased array coil was designed and built for both active MR device tracking and high‐resolution vessel wall imaging. The device consists of two independent solenoid coils that are wound in opposite directions, connected to separate receive channels, and mounted collinearly on an angiographic catheter. The elements were used independently or together for tracking or imaging applications, respectively. The array's dual functionality was tested on a clinical 1.5 T MRI scanner in vitro, in vivo, and in situ. During real‐time catheter tracking, each element gave rise to a high‐amplitude peak in the respective projection data, which enabled reliable and robust device tracking as well as automated slice positioning. In vivo microimaging with 240 μm in‐plane resolution was achieved in 9 s using the device and TrueFISP imaging. Therefore, a single device was successfully implemented that met the combined requirements of intravascular device tracking and imaging. Magn Reson Med 51:668–675, 2004. © 2004 Wiley‐Liss, Inc.
Real‐time cardiac MRI at 3 tesla
Authors: Nayak Krishna S. , Cunningham Charles H. , Santos Juan M. , Pauly John M. 
Published: March 2004

AbstractReal‐time cardiac and coronary MRI at 1.5T is relatively “signal starved” and the 3T platform is attractive for its immediate factor of two increase in magnetization. Cardiac imaging at 3T, however, is both subtly and significantly different from imaging at 1.5T because of increased susceptibility artifacts, differences in tissue relaxation, and RF homogeneity issues. New RF excitation and pulse sequence designs are presented which deal with the fat‐suppression requirements and off‐resonance issues at 3T. Real‐time cardiac imaging at 3T is demonstrated with high blood SNR, blood‐myocardium CNR, resolution, and image quality, using new spectral‐spatial RF pulses and fast spiral gradient echo pulse sequences. The proposed sequence achieves 1.5 mm in‐plane resolution over a 20 cm FOV, with a 5.52 mm measured slice thickness and 32 dB of lipid suppression. Complete images are acquired every 120 ms and are reconstructed and displayed at 24 frames/sec using a sliding window. Results from healthy volunteers show improved image quality, a 53% improvement in blood SNR efficiency, and a 232% improvement in blood‐myocardium CNR efficiency compared to 1.5T. Magn Reson Med 51:655–660, 2004. © 2004 Wiley‐Liss, Inc.
Inversion recovery TrueFISP: Quantification of T1, T2, and spin density
Authors: Schmitt Peter , Griswold Mark A. , Jakob Peter M. , Kotas Markus , Gulani Vikas , Flentje Michael , Haase Axel 
Published: March 2004

AbstractA novel procedure is proposed to extract T1, T2, and relative spin density from the signal time course sampled with a series of TrueFISP images after spin inversion. Generally, the recovery of the magnetization during continuous TrueFISP imaging can be described in good approximation by a three parameter monoexponential function S(t) = Sstst(1‐INV exp(‐t/T). This apparent relaxation time T ≤ T1 depends on the flip angle as well as on both T1 and T2. Here, it is shown that the ratio T1/T2 can be directly extracted from the inversion factor INV, which describes the relation of the signal value extrapolated to t = 0 and the steady‐state signal. Analytical expressions are given for the derivation of T1, T2, and relative spin density directly from the fit parameters. Phantom results show excellent agreement with single point reference measurements. In human volunteers T1, T2, and spin density maps in agreement with literature values were obtained. Magn Reson Med 51:661–667, 2004. © 2004 Wiley‐Liss, Inc.
Handling constraints using multiobjective optimization concepts
Authors: Aguirre Arturo Hernández , Rionda Salvador Botello , Coello Coello Carlos A. , Lizárraga Giovanni Lizárraga , Montes Efrén Mezura 
Published: March 2004

AbstractIn this paper, we propose a new constraint‐handling technique for evolutionary algorithms which we call inverted‐shrinkable PAES (IS‐PAES). This approach combines the use of multiobjective optimization concepts with a mechanism that focuses the search effort onto specific areas of the feasible region by shrinking the constrained search space. IS‐PAES also uses an adaptive grid to store the solutions found, but has a more efficient memory‐management scheme than its ancestor (the Pareto archived evolution strategy for multiobjective optimization). The proposed approach is validated using several examples taken from the standard evolutionary and engineering optimization literature. Comparisons are provided with respect to the stochastic ranking method (one of the most competitive constraint‐handling approaches used with evolutionary algorithms currently available) and with respect to other four multiobjective‐based constraint‐handling techniques. Copyright© 2004 John Wiley & Sons, Ltd.
A fast boundary cloud method for 3D exterior electrostatic analysis
Authors: Shrivastava Vaishali , Aluru N. R. 
Published: March 2004

AbstractAn accelerated boundary cloud method (BCM) for boundary‐only analysis of 3D electrostatic problems is presented here. BCM uses scattered points unlike the classical boundary element method (BEM) which uses boundary elements to discretize the surface of the conductors. BCM combines the weighted least‐squares approach for the construction of approximation functions with a boundary integral formulation for the governing equations. A linear base interpolating polynomial that can vary from cloud to cloud is employed. The boundary integrals are computed by using a cell structure and different schemes have been used to evaluate the weakly singular and non‐singular integrals. A singular value decomposition (SVD) based acceleration technique is employed to solve the dense linear system of equations arising in BCM. The performance of BCM is compared with BEM for several 3D examples. Copyright © 2004 John Wiley & Sons, Ltd.
Preparation of N‐n‐Octyl‐D‐glucamine by the catalytic hydrogenation with palladium complex of MgO‐supported melamine‐formaldehyde polymer
Authors: Liu Pu , Zhu Weiwei 
Published: March 2004

AbstractThe palladium complex of MgO‐supported melamine‐formaldehyde polymer catalyst was prepared and characterized by X‐ray diffraction (XRD) and X‐ray photoelectron spectroscopy (XPS). The preparation of N‐n‐octyl‐D‐glucamine was investigated by using this complex as the catalyst. It was found that the palladium complex of MgO‐supported melamine‐formaldehyde polymer has a good catalytic activity for the hydrogenation of n‐octylamine with D‐glucose to produce N‐n‐octyl‐D‐glucamine. The effects of additive, solvent, temperature, hydrogen pressure, Pd content in the catalyst and the amount of catalyst on the preparation of N‐n‐octyl‐D‐glucamine have all been studied. Under the optimum experimental conditions—D‐glucose, 37.2 mmol; n‐octylamine, 31 mmol; triethylamine, 1.0 ml; ethanol, 60 ml; temperature, 333 K; hydrogen pressure, 1.5 MPa; the amount of the catalyst (Pd content 3.55%, N/Pd molar ratio 12), 0.7 g—the highest yield of N‐n‐octyl‐D‐glucamine (57.6%) was obtained. XRD results show that melamine‐formaldehyde polymer changed the structure of MgO, and XPS results suggest that coordination bonds were formed between the hexatomic ring and metal atom, and palladium particles were immobilized on the polymer. Copyright © 2004 John Wiley & Sons, Ltd.
Polystyrene prepared by reactive extrusion: kinetics and effect of processing parameters
Authors: Shishuang Gao , Ying Zhang , Anna Zheng , Xiao Huining 
Published: March 2004

AbstractThe conversion and residence time were investigated during the bulk polymerization of styrene in a twin screw extruder. It was found that polymerization mainly occurred in the zone between 400 and 1000 mm along the screw axis in the extruder, corresponding to the residence time of the reactants ranging from 1 to 4 min in the extruder. Furthermore, the processing conditions (feed rate, screw rotation rate) and average molecular weight of the polymer have a great effect on the residence time. Based on dimensionless analysis, a model of the residence time has been built‐up, which has been confirmed by the results of realistic measurements. A kinetic model of the polymerization has also been established under the assumption that the screw extruder can be regarded as an ideal plug flow reactor. Copyright © 2004 John Wiley & Sons, Ltd.
The role of thiophosphoryl disulfide on the co‐cure of CR‐EPDM blends
Authors: Das Amit , Ghosh Arup Kumar , Pal Sudipta , Basu Dipak Kumar 
Published: March 2004

AbstractBis(diisopropyl)thiophosphoryl disulfide (DIPDIS) has been used as a coupling cum curing agent for the compatibilization of blends of ethylene propylene diene monomer rubber (EPDM) with chloroprene rubber (CR). Electrical and mechanical properties of the blend vulcanizates have been studied to find the efficiency of the vulcanizing cum coupling activity of DIPDIS. The study reveals that CR in the presence of DIPDIS greatly improves the physical properties of EPDM. It is noted that the physical properties of the vulcanizates obtained from CR‐EPDM blend depend upon CR:EPDM ratio. The scanning electron microscopy (SEM) study reveals that it is possible to form a coherent blend of CR and EPDM in the presence of DIPDIS. Copyright © 2004 John Wiley & Sons, Ltd.
Effect of maleic anhydride and liquid natural rubber as compatibilizers on the mechanical properties and impact resistance of the NR‐NBR blend
Authors: Mounir Ahmed , Darwish Nabila A. , Shehata Adel 
Published: March 2004

AbstractThe degree of compatibilization between natural rubber (NR) and acrylonitrile‐butadiene rubber (NBR) was investigated by two different methods. NBR was chemically modified with maleic anhydride in a screw twin mixer with and without reaction initiator, benzoyl peroxide. Also, the effects of molecular weight of liquid natural rubber (LNR) as a compatibilizer were studied. The degree of compatibilization between NBR and NR is determined indirectly through measurements of mechanical properties and impact resistance. The maleic anhydride and benzoyl peroxide concentrations influence the mechanical properties and impact resistance of the blends. Also, the mechanical properties of the blends showed that the molecular weight of LNR played an important role in determing their performance. Copyright © 2004 John Wiley & Sons, Ltd.
A novel hyperbranched polyester acrylate used for microfabrications
Authors: Kou Huiguang , Asif Anila , Shi Wenfang , Jiang Zhongwei , Huang Wenhao 
Published: March 2004

AbstractA novel hyperbranched polyester acrylate (HPEA) was synthesized based upon ethylenediamine tetraacetic acid as a “core” molecule, 5‐hydroxyisophthalic acid as an AB2 monomer, and 2‐hydroxyethyl acrylate as an endcapping reagent. The obtained oligomer has an unsaturation concentration of 4.10 mmolCC g−1 measured by nuclear magnetic resonance and a wide molecular weight distribution of 1.64 measured by gel permeation chromatography. The two‐photon absorption (TPA) photopolymerization of HPEA under the exposure of a Ti : sapphire femtosecond laser with a wavelength of 800 nm was investigated through laser exposure dose‐dependant spatial resolutions of its resins. The TPA photopolymerization thresholds at the range 1.6–4.3 × 107 mJ cm−2, and exposure dose windows at the range 3.4–4.3 for three formulations were determined. A spatial resolution of 0.85 μm was obtained through the TPA photopolymerization of the formulation containing 1 wt% photoinitiator and 0.3 wt% photoinhibitor. A diffraction grating and real three‐dimensional coupled gear wheel created by TPA photopolymerization were described to demonstrate the unique capability of HPEA in microfabrications. Copyright © 2004 John Wiley & Sons, Ltd.
Study of interphase in glass fiber–reinforced poly(butylene terephthalate) composites
Authors: Bergeret A. , Bozec M. P. , Quantin J.‐C. , Crespy A. , Gasca J.‐P. , Arpin M. 
Published: March 2004

AbstractIt is well known that application of a coupling agent to a glass fiber surface will improve fiber/matrix adhesion in composites. However, on commercial glass fibers the coupling agent forms only a small fraction of the coating, the larger part being a mixture of processing aids whose contribution to composite properties is not well defined. The interfacial region of the composite will therefore be affected by the coating composition but also by the chemical reactions involved in the vicinity of the fiber and inside the surrounding matrix. The main feature of this study consists in dividing the interface region into two separate regions: the fiber/sizing interphase and the sizing/matrix interphase. A wide range of techniques was used, including mechanical and thermomechanical tests, infrared spectroscopy, gel permeation chromatography, carboxyl end group titrations, extraction rate measurements, and viscosity analysis. Experiments were performed on poly(butylene terephthalate) composites and results indicate that the adhesion improvement is due to the presence of a short chain coupling agent and of a polyfunctional additive, which may react both with the coupling agent and the matrix. According to the nature of this additive, it may be possible to soften the interphase and then to increase the composite impact strength.
Thermal control system for thick composite laminates based on forecasting
Authors: Shin Daniel D. , Hahn H. Thomas 
Published: March 2004

AbstractA forecast‐based thermal control system was developed to cure thick composite laminates that produced large exothermic reactions. The system used process simulation models for heat transfer and compaction to predict future cure conditions at a designated forecast time so that the system can respond to avoid approaching adverse conditions. The thermal control system derived cure cycles that eliminated exotherms and maintained uniform through‐the‐thickness temperature gradient for 3‐cm thick AS4/35016 laminates. The on‐line results indicated that cure cycles were slightly different from off‐line simulation results, mainly because of the slow response of the hot press. Nevertheless the system was able to satisfy the cure criteria under such unforeseen circumstances, which demonstrated the flexibility of the forecasting method.
Effects of styrene‐isoprene copolymer glass fiber coatings on woven glass cloth epoxy composite performance
Authors: Blakley Kevin L. , Grady Brian P. , O'Rear Edgar A. 
Published: March 2004

AbstractWoven glass‐epoxy composites were prepared from mats that had been treated in a variety of ways. Fibers were coated with a commercial sizing, no sizing, and a surfactant coating. In addition, fibers were coated with styrene‐isoprene copolymers at varying molar ratios using a novel technique termed admicellar polymerization. Dynamic contact angle measurements were used to quantify the effect of the different coating techniques on the fiber, while dynamic mechanical analysis (DMA) and flexural testing were used to characterize the cured composites. Wetting studies conducted with EPON 828 resin revealed no difference in wetting for the polymer‐treated fiber compared to the commercially‐treated fiber. Aqueous wetting results were consistent with a surfactant layer adsorbed on the polymer treated and surfactant treated fiber surface. DMA established that both the polymer and surfactant treatment depressed the alpha transition temperature of the composite and suggested an interpenetrating network existed at the fiber‐matrix interface. Flexural strength testing showed the properties of the composites made from surfactant‐treated and polymer‐treated glass fibers were comparable to composites made from commercially‐sized fibers and exceeded the flexural strength of the composite made from glass fibers without sizing.