bluuebunny/crossref_metadata_2025_split huggingface dataset:
Monitoring of brain potassium with rubidium flame photometry and MRI
Authors: Yushmanov Victor E. , Kharlamov Alexander , Boada Fernando E. , Jones Stephen C. 
Published: February 2007

AbstractAn animal model was developed to monitor [K+] in the brain using partial K+ replacement with Rb+ and 87Rb MRI. Fifty‐one rats were given 0–80 mM of RbCl in the drinking water for up to 90 days. Focal cerebral ischemia was produced in 15 of the animals. Na, K, and Rb content in precision‐guided submilligram samples of cortical brain were determined by emission flame photometry. Multinuclear 87Rb/23Na/1H MRI was performed on phantoms and rats at 3T using a twisted projection imaging (TPI) scheme for 87Rb/23Na, and custom‐built surface or parallel cosine transmit/receive coils. Brain [Rb+] was safely brought up to 17–25 mEq/kg within 2–3 weeks of feeding. The characteristic patterns of [K+] decrease (with a sharp drop at 3–4 hr of ischemia) and [Na+] increase (at a rate of 31%/hr) observed previously in animals without Rb/K substitution were reproduced in ischemic cortex. The Rb/(Rb+K) ratio increased over time in ischemic areas (R = 0.91, P < 0.001), suggesting an additional index of ischemia progression. Preliminary 87Rb MRI gave an estimate of 20–25 mEq Rb/kg brain weight (N = 2). In conclusion, brain Rb+ is detectable by 87Rb MRI and does not significantly interfere with ion dynamics in ischemic brain, which enables 87Rb MRI studies of K+ in ischemia. Magn Reson Med 57:494–500, 2007. © 2007 Wiley‐Liss, Inc.
Adiabatic refocusing pulses for volume selection in magnetic resonance spectroscopic imaging
Authors: Sacolick Laura I. , Rothman Douglas L. , de Graaf Robin A. 
Published: February 2007

AbstractBecause of their excellent slice profiles and high immunity to RF inhomogeneity, adiabatic full passage (AFP) pulses are ideal for use in spatial localization. The nonlinear, position‐dependent phase of a single AFP pulse generated during refocusing of transverse magnetization traditionally is eliminated by using identical pairs of AFP pulses, at the expense of increased RF power deposition and increased echo time (TE). Here it is shown that one can achieve significant phase refocusing by executing single AFP pulses along non‐equivalent spatial axes. When used for volume selection in MR spectroscopic imaging (MRSI) the remaining nonlinear phase becomes inconsequential when the phase across a spectroscopic volume is small. Selection of rectangular and octagonal volumes is demonstrated with half the number of AFP pulses used in the traditional approach. It is shown that octagonal volume selection in the human brain provides excellent suppression of extracranial lipids, and thus allows multislice 1H MRSI at 4 Tesla to be performed within the guidelines for RF power deposition. Magn Reson Med 57:548–553, 2007. © 2007 Wiley‐Liss, Inc.
Is the “biexponential diffusion” biexponential?
Authors: Kiselev Valerij G. , Il'yasov Kamil A. 
Published: February 2007

AbstractDiffusion‐weighted signal from the brain,S, deviates from monoexponential dependence on theb‐factor. This property is often referred to as biexponential diffusion, since the corresponding model fits data well. The aim of this study is to examine the necessity of using the biexponential model in homogeneous voxels under isotropic diffusion weighting up tob= 2.5 ms/μm2. The model is compared to the cumulant expansion of lnSin a power series inb, which takes its origin in fundamental properties of the diffusion‐weighted signal, but diverges at largeb. The absence of statistically significant evidences for the biexponential diffusion is demonstrated in gray matter. The cumulant expansion terminated after the termb2describes data equally well with fewer adjustable parameters. The biexponential model is preferable in voxels with a partial volume of CSF. Magn Reson Med 57:464–469, 2007. © 2007 Wiley‐Liss, Inc.
Novel method for rapid, simultaneous T1, T*2, and proton density quantification
Authors: Warntjes J.B.M. , Dahlqvist O. , Lundberg P. 
Published: February 2007

AbstractAn imaging method called “quantification of relaxation times and proton density by twin‐echo saturation‐recovery turbo‐field echo” (QRAPTEST) is presented as a means of quickly determining the longitudinal T1 and transverse T relaxation time and proton density (PD) within a single sequence. The method also includes an estimation of the B1 field inhomogeneity. High‐resolution images covering large volumes can be achieved within clinically acceptable times of 5–10 min. The range of accuracy for determining T1, T, and PD values is flexible and can be optimized relative to any anticipated values. We validated the experimental results against existing methods, and provide a clinical example in which quantification of the whole brain using 1.5 mm3 voxels was achieved in less than 8 min. Magn Reson Med 57:528–537, 2007. © 2007 Wiley‐Liss, Inc.
Inversion recovery prepared turbo spin echo sequences with reduced SAR using smooth transitions between pseudo steady states
Authors: Weigel Matthias , Zaitsev Maxim , Hennig Juergen 
Published: February 2007

AbstractThis study investigates the contrast behavior of 2D inversion recovery (IR) prepared turbo spin echo (TSE) sequences that use RF pulse schemes with variable low flip angles (hyperTSE) to reduce RF power deposition. A framework of equations and calculations for adapting the sequence parameters is presented by which equivalent image contrast is achieved compared to conventional IR‐TSE imaging. Although the inversion time (TI) and repetition time (TR) do not need to be changed, the echo time (TE) has to be prolonged such that the effective TE (TEeff) is preserved. Measurements in healthy volunteers confirmed this finding for IR‐TSE sequences using different TIs: fluid attenuated inversion recovery (FLAIR), gray matter (GM)‐white matter (WM)‐IR, and short tau IR (STIR). The results demonstrate that hyperTSE sequences enable high‐quality IR‐prepared imaging with a considerably reduced specific absorption rate (SAR). Magn Reson Med 57:631–637, 2007. © 2007 Wiley‐Liss, Inc.
Flow‐metabolism coupling in human visual, motor, and supplementary motor areas assessed by magnetic resonance imaging
Authors: Chiarelli Peter A. , Bulte Daniel P. , Gallichan Daniel , Piechnik Stefan K. , Wise Richard , Jezzard Peter 
Published: February 2007

AbstractCombined blood oxygenation level‐dependent (BOLD) and arterial spin labeling (ASL) functional MRI (fMRI) was performed for simultaneous investigation of neurovascular coupling in the primary visual cortex (PVC), primary motor cortex (PMC), and supplementary motor area (SMA). The hypercapnia‐calibrated method was employed to estimate the fractional change in cerebral metabolic rate of oxygen consumption (CMRO2) using both a group‐average and a per‐subject calibration. The group‐averaged calibration showed significantly different CMRO2−CBF coupling ratios in the three regions (PVC: 0.34 ± 0.03; PMC: 0.24 ± 0.03; and SMA: 0.40 ± 0.02). Part of this difference emerges from the calculated values of the hypercapnic calibration constant M in each region (MPVC = 6.6 ± 3.4, MPMC = 4.3 ± 3.5, and MSMA = 7.2 ± 4.1), while a relatively minor part comes from the spread and shape of the sensorimotor BOLD–CBF responses. The averages of the per‐subject calibrated CMRO2−CBF slopes were 0.40 ± 0.04 (PVC), 0.31 ± 0.03 (PMC), and 0.44 ± 0.03 (SMA). These results are 10–30% higher than group‐calibrated values, and are potentially more useful for quantifying individual differences in focal functional responses. The group‐average calibrated motor coupling value is increased to 0.28 ± 0.03 when stimulus‐correlated increases in end‐tidal CO2 are included. Our results support the existence of regional differences in neurovascular coupling, and argue for the importance of achieving optimal accuracy in hypercapnia calibrations to resolve method‐dependent variations in published results. Magn Reson Med 57:538–547, 2007. © 2007 Wiley‐Liss, Inc.
Array‐optimized composite pulse for excellent whole‐brain homogeneity in high‐field MRI
Authors: Collins Christopher M. , Wang Zhangwei , Mao Weihua , Fang Jieming , Liu Wanzhan , Smith Michael B. 
Published: February 2007

AbstractA number of methods to improve excitation homogeneity in high‐field MRI have been proposed, and some of these methods rely on separate control of radiofrequency (RF) coils in a transmit array. In this work we combine accurate RF field calculations and the Bloch equation to demonstrate that by using a sequence of pulses with individually optimized current distributions (i.e., an array‐optimized composite pulse), one can achieve remarkably homogeneous distributions of available signal intensity over the entire brain volume. This homogeneity is greater than that achievable using the same transmit array to produce either a single optimized (or RF shimmed) pulse or a single RF shimmed field distribution in a standard 90x‐90y composite pulse arrangement. Simulations indicate that with a very simple array‐optimized composite pulse, excellent whole‐brain excitation homogeneity can be achieved at up to 600 MHz. Magn Reson Med 57:470–474, 2007. © 2007 Wiley‐Liss, Inc.
Water‐ and fat‐suppressed proton projection MRI (WASPI) of rat femur bone
Authors: Wu Yaotang , Dai Guangping , Ackerman Jerome L. , Hrovat Mirko I. , Glimcher Melvin J. , Snyder Brian D. , Nazarian Ara , Chesler David A. 
Published: February 2007

AbstractInvestigators often study rats by μCT to investigate the pathogenesis and treatment of skeletal disorders in humans. However, μCT measurements provide information only on bone mineral content and not the solid matrix. CT scans are often carried out on cancellous bone, which contains a significant volume of marrow cells, stroma, water, and fat, and thus the apparent bone mineral density (BMD) does not reflect the mineral density within the matrix, where the mineral crystals are localized. Water‐ and fat‐suppressed solid‐state proton projection imaging (WASPI) was utilized in this study to image the solid matrix content (collagen, tightly bound water, and other immobile molecules) of rat femur specimens, and meet the challenges of small sample size and demanding submillimeter resolution. A method is introduced to recover the central region of k‐space, which is always lost in the receiver dead time when free induction decays (FIDs) are acquired. With this approach, points near the k‐space origin are sampled under a small number of radial projections at reduced gradient strength. The typical scan time for the current WASPI experiments was 2 hr. Proton solid‐matrix images of rat femurs with 0.4‐mm resolution and 12‐mm field of view (FOV) were obtained. This method provides a noninvasive means of studying bone matrix in small animals. Magn Reson Med 57:554–567, 2007. © 2007 Wiley‐Liss, Inc.
Optimized and combined T1 and B1 mapping technique for fast and accurate T1 quantification in contrast‐enhanced abdominal MRI
Authors: Treier Reto , Steingoetter Andreas , Fried Michael , Schwizer Werner , Boesiger Peter 
Published: February 2007

AbstractFast T1 mapping techniques are a valuable means of quantitatively assessing the distribution and dynamics of intravenously or orally applied paramagnetic contrast agents (CAs) by noninvasive imaging. In this study a fast T1 mapping technique based on the variable flip angle (VFA) approach was optimized for accurate T1 quantification in abdominal contrast‐enhanced (CE) MRI. Optimization methods were developed to maximize the signal‐to‐noise ratio (SNR) and ensure effective RF and gradient spoiling, as well as a steady state, for a defined T1 range of 100–800 ms and a limited acquisition time. We corrected B1 field inhomogeneities by performing an additional measurement using an optimized fast B1 mapping technique. High‐precision in vitro and abdominal in vivo T1 maps were successfully generated at a voxel size of 2.8 × 2.8 × 15 mm3 and a temporal resolution of 2.3 s per T1 map on 1.5T and 3T MRI systems. The application of the proposed fast T1 mapping technique in abdominal CE‐MRI enables noninvasive quantification of abdominal tissue perfusion and vascular permeability, and offers the possibility of quantitatively assessing dilution, distribution, and mixing processes of labeled solutions or drugs in the gastrointestinal tract. Magn Reson Med 57:568–576, 2007. © 2007 Wiley‐Liss, Inc.
Linear discriminant analysis of brain tumour 1H MR spectra: a comparison of classification using whole spectra versus metabolite quantification
Authors: Opstad K. S. , Ladroue C. , Bell B. A. , Griffiths J. R. , Howe F. A. 
Published: February 2007

Abstract1H MRS is an attractive choice for non‐invasively diagnosing brain tumours. Many studies have been performed to create an objective decision support system, but there is not yet a consensus as to the best techniques of MRS acquisition or data processing to be used for optimum classification. In this study, we investigate whether LCModel analysis of short‐TE (30 ms), single‐voxel tumour spectra provide a better input for classification than the use of the original spectra. A total of 145 histologically diagnosed brain tumour spectra were acquired [14 astrocytoma grade II (AS2), 15 astrocytoma grade III (AS3), 42 glioblastoma (GBM), 41 metastases (MET) and 33 meningioma (MNG)], and linear discriminant analyses (LDA) were performed on the LCModel analysis of the spectra and the original spectra. The results consistently suggest improvement in classification when the LCModel concentrations are used. LDA of AS2, MNG and high‐grade tumours (HG, comprising GBM and MET) correctly classified 94% using the LCModel dataset compared with 93% using the spectral dataset. The inclusion of AS3 reduced the accuracy to 82% and 78% for LCModel analysis and the original spectra, respectively, and further separating HG into GBM and MET gave 70% compared with 60%. Generally MNG spectra have profiles that are visually distinct from those of the other tumour types, but the classification accuracy was typically about 80%, with MNG with substantial lipid/macromolecule signals being classified as HG. Omission of the lipid/macromolecule concentrations in the LCModel dataset provided an improvement in classification of MNG (91% compared with 76%). In conclusion, there appears to be an advantage to performing pattern recognition on the quantitative analysis of tumour spectra rather than using the whole spectra. However, the results suggest that a two‐step LDA process may help in classifying the five tumour groups to provide optimum classification of MNG with high lipid/macromolecule contributions which maybe misclassified as HG. Copyright © 2007 John Wiley & Sons, Ltd.
Multi‐path routing scheme for non‐interactive multicast communications
Authors: Srinivasan R. , Vaidehi V. , Ranjani N. , Sathya M. , Subramani D. 
Published: February 2007

AbstractThis paper proposes a multicast routing algorithm that makes use of multiple node‐disjoint distribution trees for its routing from the source to the multicast group members. The specialty of this scheme is that the different packets of a message between a source and destinations are routed through node‐disjoint paths to provide reliable and secure multicast communication. In this proposed routing scheme the computation of the node‐disjoint path for packet routing is done either at a centralized route moderator or in a distributed fashion at all destinations in order to avoid single point failure. An effective provision is made to enable new members to join the existing multicast trees and to prune leaving members. The performance parameters of the proposed reliable and secure multi‐path routing scheme are studied under various network conditions using GloMoSim. Copyright © 2006 John Wiley & Sons, Ltd.
Generalized midpoint integration algorithms for J2 plasticity with linear hardening
Authors: Artioli E. , Auricchio F. , Beirão da Veiga L. 
Published: February 2007

AbstractWe consider four schemes based on generalized midpoint rule and return map algorithm for the integration of the classical J2 plasticity model with linear hardening. The comparison, aiming to establish which is the preferable scheme among the four considered, is both theoretical and numerical. On one side, extending and completing the existing results in the literature, we investigate the four schemes from the theoretical viewpoint, addressing in particular the existence of solution, long‐term behaviour, accuracy and stability. On the other hand, we develop an extensive set of numerical tests, based on pointwise stress–strain loading histories, iso‐error maps and initial boundary‐value problems. Copyright © 2007 John Wiley & Sons, Ltd.
Properties of a novel thermal sensitive polymer based on poly(vinyl alcohol) and its layer‐by‐layer assembly
Authors: Lu Hong , Zheng Anna , Xiao Huining 
Published: February 2007

AbstractStructurally modified poly(vinyl alcohol) (PVA) was prepared as novel thermally sensitive polymers by partially acetalyzing and/or ionizing the commercially available PVA. Their aqueous solutions experience completely reversible polymer aggregation and dissolution above and below the lower critical solution temperature (LCST), respectively. The LCST of a partially acetalyzed PVA (APVA) can be readily controlled by the degree of acetalysis or the molecular weight of the starting PVA. Introduction of a small amount of cationic group onto the APVA backbone increases the LCST obviously, while the LCST is highly sensitive to NaCl concentration. Then APVA and cationic APVA multilayers are assembled on rayon to make a thermal responsive fiber. The atomic force microscopy (AFM) images of the surface reveal the increment of roughness stimulated by temperature. Copyright © 2007 John Wiley & Sons, Ltd.
Hybrid proton exchange membranes based on sulfonated poly(phthalazinone ether ketone) and zirconium hydrogen phosphate
Authors: Zhang Hong‐wei , Du Chun‐hui , Xu You‐yi , Zhu Bao‐ku 
Published: February 2007

AbstractSulfonated poly(phthalazinone ether ketone)s (SPPEKs) and zirconium hydrogen phosphate (ZrP) hybrid membranes for direct methanol fuel cells (DMFCs) were prepared by the impregnation method and direct blending method. The physicochemical properties of these hybrid membranes were studied by means of field‐emission scanning electron microscope (FSEM), X‐ray diffraction (XRD) analysis, and thermogravimetry analysis (TGA). For the hybrid membranes prepared from impregnation procedure, the highest proton conductivity could reach 0.074 S/cm at 80°C under 100% relative humidity and the methanol permeability at room temperature is more than 10 times lower than that of Nafion 117. Copyright © 2007 John Wiley & Sons, Ltd.
Co‐prescriptions with itraconazole and fluconazole as a signal for possible risk of drug–drug interactions: a four‐year analysis from Italian general practice
Authors: Galatti Laura , Mazzaglia Giampiero , Greco Antonella , Sessa Emiliano , Cricelli Claudio , Schito Gian Carlo , Nicoletti Giuseppe , Spina Edoardo , Caputi Achille P. 
Published: February 2007

AbstractPurposeTo determine the prevalence of concomitant use of drugs potentially responsible for interactions among itraconazole and fluconazole users in general practice.MethodsDuring the years 1999–2002, we obtained information from the ‘Health Search Database’, (HSD) an Italian general practice research database. Among a total sample of 457 672 eligible patients, we included those aged >16 years, and whose diagnoses could be classified as mycosis. Itraconazole and fluconazole users were then selected. A potentially drug–drug interaction (DDI) occurred when the use of concomitant drugs were recorded within ±30 days from the date of the first azoles prescription. Interacting drugs were classified according to the summary of product characteristics (SPC) as provided by the Italian Pharmaceutical Repertory (REFI).ResultsFrom 18 323 cases of mycosis, we selected 4843 itraconazole and 1446 fluconazole users. Potentially interacting drugs were prescribed in 8.7% of itraconazole and 6.1% of fluconazole users. For itraconazole, calcium channel blockers were the most common interacting drugs (3.3%), followed by statins (1.7%) and clarithromycin (1.3%), whereas gestoden + ethynylestradiol (2.5%) and benzodiazepines (1.8%) resulted as the most common interacting drugs among fluconazole users.ConclusionData indicate a relevant prevalence of concomitant use of medications potentially leading to drug interactions among azoles users. Because of the wide use of these medications in general practice, they should be used with clinical monitoring in view of their known side effects as well as their potential risk for drug interaction. Copyright © 2007 John Wiley & Sons, Ltd.
Roboter lernen Fußball spielen: Autonome Roboter
Authors: Lauer Martin , Hafner Roland 
Published: February 2007

AbstractSeit zehn Jahren gibt es jährlich die Weltmeisterschaft Robocup für autonome, fußballspielende Roboter. Inzwischen sind der mechanische Aufbau der Roboter, die Sensorauswertung und Verhaltenssteuerung per Bordrechner so weit entwickelt, dass ein echtes Fußballspiel entstehen kann. Allerdings erfordert die Übertragung der Techniken von radbasierten Robotern auf zweibeinige, humanoide Roboter noch intensive Forschung. Das gilt auch für eine technische Ausstattung, die die Entwicklung eines umfassenden taktischen Spiels ermöglicht. Trotz des ermutigenden Fortschritts ist der Weg noch weit, bis ein Fußballroboter mit menschlichen Spielern mithalten kann.
SCIAMACHY – Neue Ansichten der Erdatmosphäre: Atmosphären‐ und Klimaforschung aus dem All
Authors: Gottwald Manfred , Bovensmann Heinrich 
Published: February 2007

AbstractDas Atmosphäreninstrument SCIAMACHY auf ENVISAT ermöglicht einzigartige Untersuchungen unserer Erdatmosphäre. Erstmals können weltweit die Luftschadstoffe und Ozonvorläufersubstanzen Stickstoffdioxid, Kohlenmonoxid, Schwefeldioxid, Formaldehyd und Glyoxal global mit einer räumlichen Auflösung vermessen werden, die Aussagen über die Luftqualität einzelner Großstädte und Ballungszentren sowie die Verifikation von Emissionskatastern erlaubt. Auch wichtige Treibhausgase wie Methan und Kohlenstoffdioxid werden erstmals erfasst. Zudem sind viele bedeutende Atmosphärenparameter von der Erdoberfläche bis in die Mesosphäre zugänglich. Dazu zählt insbesondere Ozon zusammen mit global bestimmbaren dreidimensionalen Verteilungen wichtiger ozonzerstörender Substanzen wie etwa Stick‐ und Halogenoxiden.
Schnittfeste Saucenwürfel – kleckerfreie Sauce
Authors: Vilgis Thomas 
Published: February 2007

AbstractDie Diskussion bei der Nachsitzung des physikalischen Kolloquiums ist angeregt. Das Fleisch geschnitten, zum Mund geführt, und schwupp, landet ein Saucenspritzer mitten auf der neuen Krawatte. Inspiriert durch neue Trends in der Avantgardeküche ließe sich dieses Missgeschick vermeiden: kleckerfreie Saucen, schnittfest und trotzdem heiß, das wär's. Tatsächlich sind schmackhaft warme, feste Gele in der haute cuisine keine Utopie. Und aus physikalischer Sicht ist der feste Saucenwürfel ein interessantes Beispiel für einen Sol‐Gel‐Übergang.
Schwingende Nanoschichten im Röntgen‐Stroboskop
Authors: Bargheer Matias , v. Korff Schmising Clemens , Wörner Michael , Elsässer Thomas 
Published: February 2007

AbstractEine Arbeitsgruppe am Max‐Born‐Institut (MBI) in Berlin verwendet mit Hochleistungslasern erzeugte ultrakurze Röntgenimpulse, um atomare Bewegungen in Nanostrukturen stroboskopisch abzubilden. Die Methode ermöglicht simultan eine Zeitauflösung von 100 Femtosekunden und eine Ortsauflösung von 100 Femtometern.
Eine schwebende Lichtkugel in einer Kugelleuchte
Authors: Schlichting H. Joachim 
Published: February 2007

AbstractGläserne Kugelleuchten können zu Hohlspiegeln werden und von den im Innern befindlichen Lampen reelle, frei schwebende Bilder erzeugen. Dem unvorbereiteten Beobachter erscheint ein solches Bilder wie ein glühendes Plasma.