bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reduction of RF power for magnetization transfer with optimized application of RF pulses in k‐space
Authors: Lin Chen , Bernstein Matt A. , Gibbs Gordon F. , Huston John 
Published: June 2003

AbstractMore efficient use of RF power for RF‐intensive applications such as magnetization transfer (MT) is necessary at high field strength (3.0 T or greater) to keep the specific absorption rate (SAR) within regulatory limits. It has been demonstrated that RF power deposition can be reduced with minimal impact on image quality by preferential application of MT pulses to the central phase‐encoding views. This work extends that approach to both phase‐encoding directions in a 3D acquisition (i.e., phase and slice) and further improves it by modulating the flip angle of the MT pulse according to the phase‐encoded view's distance to the center of k‐space. This technique is implemented for 3D time‐of‐flight (TOF) MR angiography (MRA) and the parameters for MT pulse are optimized based on phantom studies at 3.0 T. MT applied with this method at 3.0 T is shown to improve the blood vessel detectability in high‐resolution intracranial 3D TOF MRA exams of 11 patients. Magn Reson Med 50:114–121, 2003. © 2003 Wiley‐Liss, Inc.
Quantitative magnetization transfer mapping of bound protons in multiple sclerosis
Authors: Tozer D. , Ramani A. , Barker G.J. , Davies G.R. , Miller D.H. , Tofts P.S. 
Published: June 2003

AbstractQuantitative analysis of magnetization transfer images has the potential to allow a more thorough characterization of the protons, both bound and free, in a tissue by extracting a number of parameters relating to the NMR properties of the protons and their local environment. This work develops previously presented techniques to produce estimates of parameters such as the bound proton fraction, f, and the transverse relaxation time of the bound pool, T2B, for the whole brain in a clinically acceptable imaging time. This is achieved by limiting the number of data collected (typically to 10); to collect 28 5‐mm slices with a reconstructed resolution of 0.94 × 0.94 mm. The protocol takes 82 sec per data point. The fitting technique is assessed against previous work and for fitting failures. Maps and analysis are presented from a group of seven controls and 20 multiple sclerosis patients. The maps show that the parameters are sensitive to tissue‐specific differences and can detect pathological change within lesions. Statistically significant differences in parameters such as T2B and f are seen between normal‐appearing white matter, multiple sclerosis lesions, and control white matter. Whole‐brain histograms of these parameters are also presented, showing differences between patients and controls. Magn Reson Med 50:83–91, 2003. © 2003 Wiley‐Liss, Inc.
Super‐parallel MR microscope
Authors: Matsuda Yoshimasa , Utsuzawa Shin , Kurimoto Takeaki , Haishi Tomoyuki , Yamazaki Yukako , Kose Katsumi , Anno Izumi , Marutani Mitsuhiro 
Published: June 2003

AbstractA super‐parallel MR microscope in which multiple (up to 100) samples can be imaged simultaneously at high spatial resolution is described. The system consists of a multichannel transmitter–receiver system and a gradient probe array housed in a large‐bore magnet. An eight‐channel MR microscope was constructed for verification of the system concept, and a four‐channel MR microscope was constructed for a practical application. Eight chemically fixed mouse fetuses were simultaneously imaged at the 200 μm3 voxel resolution in a 1.5 T superconducting magnet of a whole‐body MRI, and four chemically fixed human embryos were simultaneously imaged at 120 μm3 voxel resolution in a 2.35 T superconducting magnet. Although the spatial resolutions achieved were not strictly those of MR microscopy, the system design proposed here can be used to attain a much higher spatial resolution imaging of multiple samples, because higher magnetic field gradients can be generated at multiple positions in a homogeneous magnetic field. Magn Reson Med 50:183–189, 2003. © 2003 Wiley‐Liss, Inc.
Three‐dimensional BOLD fMRI with spin‐echo characteristics using T2 magnetization preparation and echo‐planar readouts
Authors: Denolin Vincent , Metens Thierry 
Published: June 2003

AbstractA new approach to mixed T2‐ and T‐weighted BOLD fMRI is presented, which combines T2 magnetization preparation (T2prep) with a series of EPI readouts. This technique allows full 3D, time‐efficient imaging to be performed with low RF power deposition. Steady‐state calculations are performed in order to study signal formation in 3D T2prep‐EPI sequences. Results obtained under the hypothesis of ideal spoiling are compared to full Bloch equation solutions. The theoretical findings are validated by means of in vitro and in vivo signal measurements. Several variants of the 3D T2prep‐EPI approach are shown to be usable for visual cortex fMRI and compared to conventional 3D coherent gradient‐echo EPI. The relative sensitivity of these sequences is shown to be predictable by means of a simple ΔT2/ΔT model. Magn Reson Med 50:132–144, 2003. © 2003 Wiley‐Liss, Inc.
Tracer arrival timing‐insensitive technique for estimating flow in MR perfusion‐weighted imaging using singular value decomposition with a block‐circulant deconvolution matrix
Authors: Wu Ona , Østergaard Leif , Weisskoff Robert M. , Benner Thomas , Rosen Bruce R. , Sorensen A. Gregory 
Published: June 2003

AbstractRelative cerebral blood flow (CBF) and tissue mean transit time (MTT) estimates from bolus‐tracking MR perfusion‐weighted imaging (PWI) have been shown to be sensitive to delay and dispersion when using singular value decomposition (SVD) with a single measured arterial input function. This study proposes a technique that is made time‐shift insensitive by the use of a block‐circulant matrix for deconvolution with (oSVD) and without (cSVD) minimization of oscillation of the derived residue function. The performances of these methods are compared with standard SVD (sSVD) in both numerical simulations and in clinically acquired data. An additional index of disturbed hemodynamics (oDelay) is proposed that represents the tracer arrival time difference between the AIF and tissue signal. Results show that PWI estimates from sSVD are weighted by tracer arrival time differences, while those from oSVD and cSVD are not. oSVD also provides estimates that are less sensitive to blood volume compared to cSVD. Using PWI data that can be routinely collected clinically, oSVD shows promise in providing tracer arrival timing‐insensitive flow estimates and hence a more specific indicator of ischemic injury. Shift maps can continue to provide a sensitive reflection of disturbed hemodynamics. Magn Reson Med 50:164–174, 2003. © 2003 Wiley‐Liss, Inc.
Detection of the anoxic depolarization of focal ischemia using manganese‐enhanced MRI
Authors: Aoki Ichio , Ebisu Toshihiko , Tanaka Chuzo , Katsuta Kiyotaka , Fujikawa Akihiko , Umeda Masahiro , Fukunaga Masaki , Takegami Tetsuro , Shapiro Erik M. , Naruse Shoji 
Published: June 2003

AbstractMismatch between diffusion‐ and perfusion‐weighted MRI was used to indicate a treatable area following focal ischemia, called the penumbra. Activity‐induced manganese contrast MRI has been reported as a new visualization method for neural activation using manganese ions as a depolarization‐dependent contrast agent. It is well known that energy failure induced by cerebral ischemia produces anoxic depolarization. The purpose of this study was to detect manganese accumulation caused by permanent middle cerebral artery occlusion (MCAO) of rat brain and to compare regional differences between manganese accumulation and decreased apparent diffusion coefficient (ADC). The ratios of signal intensity of manganese‐enhanced MRI in the ipsilateral cortex to that in the contralateral cortex were 171.0 ± 17.5% in MCAO group and 108.4 ± 13.2% in the sham group. In addition, the enhanced region was much smaller than the area which was detected as having a reduced ADC. Magn Reson Med 50:7–12, 2003. © 2003 Wiley‐Liss, Inc.
Jaco J.M. Zwanenburg, Joost P.A. Kuijer, J. Tim Marcus, Robert M. Heethaar. Steady‐state free precession with myocardial tagging: CSPAMM in a single breathhold, Magnetic Resonance in Medicine (2003)49(4):722‐730
Authors: Zwanenburg Jaco J.M. , Kuijer Joost P.A. , Marcus J. Tim , Heethaar Robert M. 
Published: June 2003

AbstractThe original article to which this Erratum refers was published in Magnetic Resonance in Medicine (2003) 49(4):722–730
Modified perturbation method for transverse electromagnetic (TEM) coil tuning and evaluation
Authors: Avdievich Nikolai I. , Krymov Vladimir N. , Hetherington Hoby P. 
Published: June 2003

AbstractA modified perturbation method for tuning and testing volume head coils was developed. The common perturbation method, utilizing the change in resonance frequency of a resonator in response to the presence of a small dielectric or magnetic probe, was modified to modulate the frequency shift due to rotation of a probe. This modification enabled the RF magnetic and electric fields as well as the angular distribution of current in the longitudinal elements of the coil to be mapped. The latter serves as a quick test of magnetic field homogeneity by comparing the measured distribution with the sinusoidal function required for the field to be homogenous. The method was experimentally applied to tune and test a transverse electromagnetic (TEM) head coil. Magn Reson Med 50:13–18, 2003. © 2003 Wiley‐Liss, Inc.
Mortuary patterns in burial caves on Mangaia, Cook Islands
Authors: Antón S. C. , Steadman D. W. 
Published: June 2003

AbstractThe behavioural, cultural, and political implications of archaeological human remains in non‐mortuary, possibly culinary, contexts requires that we understand the range of mortuary practices in a particular region. Although several rockshelter sites on Mangaia, Cook Islands have yielded burned, fragmentary human bones in earth ovens that seem to support archaeological models and ethnohistoric accounts of ritual sacrifice and cannibalism, the absence of data on the range of Mangaian mortuary patterns obscures these interpretations. We describe burial patterns based on 40 above‐ground interments representing at least 92 individuals in caves of Mangaia, Cook Islands, in order to begin to develop an island‐wide perspective on mortuary patterns. Sampling both pre‐ and post‐European contact sites we found that multiple interments dominate probable pre‐contact burials (73%, 19 of 26) and single interments dominate post‐contact contexts (80%, eight of ten burials), probably reflecting the influence of Christianity on mortuary ritual. Subadults were more frequent in all post‐contact contexts suggesting alternative burial places, probably church cemeteries, for adults. Burial cave remains are broadly consistent with ethnohistoric accounts of interment in caves, however, they also illustrate additional burial practices and differences between time periods, such as primary body position and the role of multiple‐individual interments, which are not discussed ethnohistorically. The mortuary practices in Mangaian burial caves differ from burials associated with marae and seem completely unrelated to the presence of highly fragmentary and burnt human remains in pre‐contact rockshelter middens elsewhere on the island. Copyright © 2003 John Wiley & Sons, Ltd.
Lessons from temporal variation in the mammalian faunas from two collections of owl pellets in Columbia County, Washington
Authors: Lyman R. L. , Lyman R. J. 
Published: June 2003

AbstractCollections of owl pellets deposited before and after a change in nearby habitats from producing wheat fields only to producing wheat fields and a patchy grass field were obtained from Columbia County, southeastern Washington. Pellets deposited before the change contained more than three times as many deer mice (Peromyscus maniculatus) as montane vole (Microtus montanus); pellets deposited after the change contained more than three times as many voles (M. montanus, M. longicaudus) as deer mice. The change in the ratio of deer mice to voles mirrors changes in rodent faunas in nearby areas caused by altered agricultural practices and resulting changes in vegetation. Because biologists correctly suggest the change in prey ratios could reflect variation in predation behaviours or prey availability, it is apparent that multiple lines of evidence are necessary to establish that changes in rodent faunas reflect changes in habitats. Copyright © 2003 John Wiley & Sons, Ltd.
Differential diagnosis of a prehistoric biological object from the Koster (Illinois) Site
Authors: Komar Debra , Buikstra Jane E. 
Published: June 2003

AbstractThis paper details the differential diagnosis of a biological artifact recovered from a burial within the Koster Middle Archaic site in Illinois. The burial was excavated from the Middle Archaic 3, Helton Phase component (∼5800–4900 BP). The artifact was a calcified nodule of unequivocal biological origin recovered from the pelvic region of an adult (50+ years) female. Morphological and radiographic analysis of the object resulted in the consideration of 19 possible diagnoses; all but four could be eliminated. Possible interpretations of the object as a lithopaedion, calcified lymph node, amputated ovary or simple ovarian cyst are examined in detail. Of these, calcified lymph node or amputated ovary remain most probable. Copyright © 2003 John Wiley & Sons, Ltd.
Determination of a controllable set for a class of non‐linear stochastic control systems
Authors: Liu Yazeng , Peng Shige 
Published: June 2003

AbstractA controllable set of a class of non‐linear stochastic control systems to a given set is defined. A value function associated with an optimal control problem is introduced. Under some reasonable conditions, the controllable set is characterized by a level set of the viscosity solution of a Hamilton–Jacobi–Bellman equation. Copyright © 2003 John Wiley & Sons, Ltd.
Discrete‐time polynomial systems approach to combined fault monitoring and control
Authors: Grimble M. J. 
Published: June 2003

AbstractThe combined fault monitoring and control problem is discussed, using an H2 optimization framework. The main aim is to investigate the frequency‐domain and pole‐zero properties of the combined control and fault estimation compensator. The solution of the LQG stochastic optimal multivariable control and fault estimation problem is obtained using a polynomial matrix systems approach. The combined control and fault estimation problem involves a performance index including the usual regulating error and control weighting terms and also fault estimation error terms. The system model includes input disturbances, reference, coloured noise signals and actuator/sensor fault signals. The proposed numerical algorithm has common polynomial terms, so that the computation of the fault estimates and control law, is not significantly more difficult than the calculation of the control law alone. Copyright © 2003 John Wiley & Sons, Ltd.
A new method for mixedH2/H∞control with regional pole constraints
Authors: Wu Jenq‐Lang , Lee Tsu‐Tian 
Published: June 2003

AbstractIn this paper, the problem of state feedback mixedH2/H∞control with regional pole constraints is studied. The constraint region is represented by several algebraic inequalities. This constrained optimization problem cannot be solved via the LMI approach. Based on the barrier method, we instead solve an auxiliary minimization problem to get an approximate solution. We shall show that the obtained minimal solution of the auxiliary minimization problem can be arbitrarily close to the infimal solution of the original problem. An example is provided to illustrate the benefits of the approach. Copyright © 2003 John Wiley & Sons, Ltd.
Simulation of pedestrian flows by optimal control and differential games
Authors: Hoogendoorn Serge , H.L. Bovy Piet 
Published: June 2003

AbstractGaining insights into pedestrian flow operations and assessment tools for pedestrian walking speeds and comfort is important in, for instance, planning and geometric design of infrastructural facilities, as well as for management of pedestrian flows under regular and safety‐critical circumstances. Pedestrian flow operations are complex, and vehicular flow simulation modelling approaches are generally not applicable to pedestrian flow modelling. This article focusses on pedestrian walking behaviour theory and modelling. It is assumed that pedestrians are autonomous predictive controllers that minimize the subjective predicted cost of walking. Pedestrians predict the behaviour of other pedestrians based on their observations of the current state as well as predictions of the future state, given the assumed walking strategy of other pedestrians in their direct neighbourhood. As such, walking can be represented by a (non‐co‐operative or co‐operative) differential game, where pedestrians may or may not be aware of the walking strategy of the other pedestrians. Copyright © 2003 John Wiley & Sons, Ltd.
Self‐diffusion of styrene, 2,2′‐azobisisobutyronitrile, and polystyrene in bulk polymerization by pulsed‐gradient spin‐echo nuclear magnetic resonance spectroscopy
Authors: Arcos‐Casarrubias José Antonio , Olayo Roberto 
Published: June 2003

AbstractThe self‐diffusion of styrene, polystyrene, and 2,2′‐azobisisobutyronitrile has been determined in the bulk polymerization of styrene with pulsed‐gradient spin‐echo nuclear magnetic resonance at 25 °C. Data on small molecules are discussed with respect to recent diffusion models. They can fit self‐diffusion coefficient data of small molecules in dilute or semidilute polymer solutions; in concentrated solutions, however, there is a breakdown. A semiempirical model based on scaling laws is used to describe the self‐diffusion of styrene and 2,2′‐azobisisobutyronitrile over the whole range of concentrations studied. The dependence of the polystyrene self‐diffusion coefficient on the polymer concentration is described with a stretched exponential function, D = D0 exp(−αcν), where α depends on the molecular weight of the polymer and ν depends on the kind of solvent. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1605–1614, 2003
Network structure and swelling behavior of poly(acrylamide/crotonic acid) hydrogels in aqueous salt solutions
Authors: Çaykara Tuncer , Bozkaya Uğur , Kantoğlu Ömer 
Published: June 2003

AbstractHydrogels with various ionic group contents were prepared from acrylamide and crotonic acid (CrA) monomers with 0–12.9 mol % CrA in aqueous solutions by radiation‐induced polymerization and gelation with γ rays from a 60Co source. The volume swelling ratio of the poly(acrylamide/crotonic acid) hydrogels was investigated as a function of the pH and ionic strength of the swelling medium and the type of counterion in the swelling medium. The volume swelling ratio increased with an increase in pH and a decrease in the ionic strength. The volume swelling ratio of these hydrogels was evaluated with an equation, based on the Flory–Huggins thermodynamic theory, the James–Guth phantom network theory, and the Donnan theory of swelling of weakly charged ionic gels, that was modified here for the determination of the molecular weight between crosslinks (Mc) and the polymer–solvent interaction parameter (χ). The modified equation described very well the swelling behavior of the charged polymeric network. The same equation also provided the simultaneous measurement of these parameters for the systems investigated. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1656–1664, 2003
Viscoelastic properties of nanostructured natural rubber/polystyrene interpenetrating polymer networks
Authors: Mathew Aji P. , Groeninckx Gabriel , Michler G. H. , Radusch H. J. , Thomas Sabu 
Published: June 2003

AbstractThe effects of the blend ratio and initiating system on the viscoelastic properties of nanostructured natural rubber/polystyrene‐based interpenetrating polymer networks (IPNs) were investigated in the temperature range of −80 to 150 °C. The studies were carried out at different frequencies (100, 50, 10, 1, and 0.1 Hz), and their effects on the damping and storage and loss moduli were analyzed. In all cases, tan δ and the storage and loss moduli showed two distinct transitions corresponding to natural rubber and polystyrene phases, which indicated that the system was not miscible on the molecular level. However, a slight inward shift was observed in the IPNs, with respect to the glass‐transition temperatures (Tg's) of the virgin polymers, showing a certain degree of miscibility or intermixing between the two phases. When the frequency increased from 0.1 to 100 Hz, theTgvalues showed a positive shift in all cases. In a comparison of the three initiating systems (dicumyl peroxide, benzoyl peroxide, and azobisisobutyronitrile), the dicumyl peroxide system showed the highest modulus. The morphology of the IPNs was analyzed with transmission electron microscopy. The micrographs indicated that the system was nanostructured. An attempt was made to relate the viscoelastic behavior to the morphology of the IPNs. Various models, such as the series, parallel, Halpin–Tsai, Kerner, Coran, Takayanagi, and Davies models, were used to model the viscoelastic data. The area under the linear loss modulus curve was larger than that obtained by group contribution analysis; this showed that the damping was influenced by the phase morphology, dual‐phase continuity, and crosslinking of the phases. Finally, the homogeneity of the system was further evaluated with Cole–Cole analysis. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1680–1696, 2003
Effect of annealing on the viscoelastic and viscoplastic responses of low‐density polyethylene
Authors: Drozdov Aleksey D. , Yuan Qiang 
Published: June 2003

AbstractTwo series of tensile tests with constant crosshead speeds (ranging from 5 to 200 mm/min) and tensile relaxation tests (at strains from 0.03 to 0.09) were performed on low‐density polyethylene in the subyield region of deformations at room temperature. Mechanical tests were carried out on nonannealed specimens and on samples annealed for 24 h at the temperatures T = 50, 60, 70, 80, and 100 °C. Constitutive equations were derived for the time‐dependent response of semicrystalline polymers at isothermal deformations with small strains. A polymer is treated as an equivalent heterogeneous network of chains bridged by temporary junctions (entanglements, physical crosslinks, and lamellar blocks). The network is thought of as an ensemble of mesoregions linked with each other. The viscoelastic behavior of a polymer is modeled as a thermally induced rearrangement of strands (separation of active strands from temporary junctions and merging of dangling strands with the network). The viscoplastic response reflects sliding of junctions in the network with respect to their reference positions driven by macrostrains. Stress‐strain relations involve five material constants that were found by fitting the observations. Fair agreement was demonstrated between the experimental data and the results of numerical simulation. This study focuses on the effects of strain rate and annealing temperature on the adjustable parameters in the constitutive equations. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1638–1655, 2003