bluuebunny/crossref_metadata_2025_split huggingface dataset:
Functional MRI of somatosensory activation in rat: Effect of hypercapnic tip‐regulation on perfusion‐ and BOLD‐imaging
Authors: Bock Christian , Schmitz Bernd , Kerskens Christian M. , Gyngell Michael L. , Hossmann Konstantin‐Alexander , Hoehn‐Berlage Mathias 
Published: March 2007

AbstractFunctional activation of somatosensory cortex was studied in α‐chloralose anesthetized rats by functional magnetic resonance imaging (fMRI), using both perfusion–weighted and T2*–weighted (blood oxygenation level dependent, BOLD) imaging. The sensitivity of functional activation was altered by ventilating animals for 3 minutes with 6% CO2. Before hyper–capnic conditioning, electrical stimulation of the left forepaw at a frequency of 3 Hz led to an increase of signal intensity (relative to the unstimulated baseline condition) in the right somatosensory cortex by 6 ± 2% (means ± SD) in T2*–weighted images and by 45% ± 48% in perfusion–weighted images. After hypercapnic conditioning the signal intensity increase in perfusion–weighted images doubled to 91% ± 62% (P = 0.034), whereas that of T2*–weighted images only marginally increased to 7 ± 4% (not significant). This different behavior in both imaging modalities is interpreted as evidence for an increased flow response in combination with a higher oxygen extraction. Thus, the fMRI data reflect hypercapniainduced resetting of the functional–metabolic coupling of the tissue during activation.
Fast imaging of phosphocreatine using a RARE pulse sequence
Authors: Greenman Robert L. , Elliott Mark A. , Vandenborne Krista , Schnall Mitchell D. , Lenkinski Robert E. 
Published: March 2007

AbstractA technique is described for acquiring phosphocreatine (PCr) images of skeletal muscle using a rapid acquisition with relaxation enhancement (RARE) pulse sequence. All of the phosphorus metabolites other than PCr are forced to dephase within the first few echoes, whereas the Carr‐Purcell Mei‐boom‐Gill (CPMG) pulse sequence maintains a high PCr signal long enough to acquire 64 echoes in a single shot. Axial PCr images of a human forearm with a signal‐to‐noise ratio of 9 were acquired in 2 min. The effect of the refocusing pulse section profile on the ratio of desired to undesired metabolite signal is demonstrated.
Dynamics of blood flow and oxygenation changes during brain activation: The balloon model
Authors: Buxton Richard B. , Wong Eric C. , Frank Lawrence R. 
Published: March 2007

AbstractA biomechanical model is presented for the dynamic changes in deoxyhemoglobin content during brain activation. The model incorporates the conflicting effects of dynamic changes in both blood oxygenation and blood volume. Calculations based on the model show pronounced transients in the deoxyhemoglobin content and the blood oxygenation level dependent (BOLD) signal measured with functional MRI, including initial dips and overshoots and a prolonged post‐stimulus undershoot of the BOLD signal. Furthermore, these transient effects can occur in the presence of tight coupling of cerebral blood flow and oxygen metabolism throughout the activation period. An initial test of the model against experimental measurements of flow and BOLD changes during a finger‐tapping task showed good agreement.
MRI of hyperpolarized 3He gas in human paranasal sinuses
Authors: Rizi Rahim R. , Dimitrov Ivan E. , Thompson Alan , Jones Gordon , Gentile Tom R. , Ishii Masaru , Reddy Ravinder , Schnall Mitchell D. , Leigh John S. 
Published: March 2007

AbstractIn this study, MRI of hyperpolarized 3He gas in human para‐nasal sinuses is presented. Helium images were obtained at 1.5 T, using a surface coil and a 2D, fast gradient‐echo sequence with a nominal constant flip angle of 12°. Coronal images of 20‐mm thick slices were generated and compared with proton images of the corresponding sections. The images enable visualization of the paranasal sinuses and the nasal cavity, suggesting a potential use of this method not only in identifying the anatomical configuration of these pneumatic spaces, but also in assessing sinus ventilation.
Temporal and regional changes during focal ischemia in rat brain studied by proton spectroscopic imaging and quantitative diffusion NMR imaging
Authors: Dreher Wolfgang , Kühn Bernd , Gyngell Michael L. , Busch Elmar , Niendorf Thoralf , Hossmann Konstantin‐Alexander , Leibfritz Dieter 
Published: March 2007

AbstractThe early development of focal ischemia after permanent occlusion of the right middle cerebral artery (MCA) was studied in six rats using interleaved measurements by diffusion‐weighted NMR imaging (DWI) of water and two variants of proton spectroscopic imaging (SI), multiecho SI (TE: 136, 272, 408 ms) and short TE SI (TE: 20 ms). Measurements on a 4.7‐T NMR imaging system were performed between the control phase and approximately 6 h postocclusion. In the center of the ischemic lesion of all rats, the apparent diffusion coefficient (ADC) decreased rapidly to 84.4 ± 4.2% (mean ± SD) of the control values approximately 2 min postocclusion. Approximately 6 h postocclusion, the ADC was reduced to 67.1 ± 5.9%. In contrast, large differences between the animals were observed for the temporal increase of lactate (Lac) in the ipsilateral hemisphere. The maximum Lac signal was reached in four rats after 0.5‐1.5 h, and in two rats was not reached even after 6 h postocclusion. Six h postocclusion, SI spectra measured at a TE of 136 ms revealed a decrease in the CH3 signal of N‐acetylaspartate (NAA) to 67 ± 13% of the control values. Differences were observed between the spatial regions of decreased NAA and increased Lac. In the lesions, a T2 relaxation time of Lac of 292 ± 40 ms, considering a J‐cou‐pling constant of 6.9 Hz, was measured. Furthermore, a prolongation of the T2 of the CH3 signal of creatine/phosphocre‐atine (Cr/PCr) was observed in the lesion, from 163 ± 22 ms during control to 211 ± 41 ms approximately 6 h postocclusion. The experiments proved that DWI and proton SI are valuable tools to provide complementary information on processes associated with brain infarcts.
A quantitative method for fast diffusion imaging using magnetization‐prepared turboFLASH
Authors: Thomas David L. , Pell Gaby S. , Lythgoe Mark F. , Gadian David G. , Ordidge Roger J. 
Published: March 2007

AbstractFor the in vivo measurement of the apparent diffusion coefficient (ADC), it is desirable for the total imaging time to be as short as possible. One technique is based on a TurboFLASH acquisition in which the diffusion gradients are inserted into a driven equilibrium Fourier transform (DEFT) combination of hard pulses. However, this sequence has the disadvantage that eddy current‐induced inhomogeneities lead to incomplete refocusing of the magnetization during the diffusion preparation and to incorrect ADC values. A modification to the sequence is suggested that eliminates this error by phase‐cycling the second 90° pulse of the preparation. This study also investigates the effect of a reduced delay time between acquisitions on the accuracy of the measurement. The quality of the TurboFLASH sequence is demonstrated by experimental validation on an agar phantom and in vivo on the rat brain using a high‐field (8.5 T) system. Reduction of the interexperiment delay time is shown to be achievable to a certain degree without compromising the measurement accuracy.
Volumetric analysis of white matter, gray matter, and CSF using fractional volume analysis
Authors: Bedell Barry J. , Narayana Ponnada A. 
Published: March 2007

AbstractQuantitative cerebral tissue volumes may be useful for an objective assessment of pathological changes in brain. Accurate determination of tissue volumes is complicated, however, by the partial volume averaging (PVA) effect. We have, therefore, developed a new pulse sequence that minimizes the PVA through the use of inversion‐recovery (IR) and double inversion‐recovery (DIR) techniques. This pulse sequence simultaneously acquires four different sets of images to provide the necessary information for volumetric analysis and reduces potential spatial misregistration of images due to patient motion. The image sets acquired from the proposed pulse sequence are 1) gray matter visible, 2) white matter visible, 3) FLAIR, and 4) fast spin‐echo proton‐density weighted images. An algorithm has been implemented to correct for differential T1‐weighting and for tissue quantitation.
Optimal design of gradient coils in MR imaging: Optimizing coil performance versus minimizing cost functions
Authors: Du Yiping P. , Parker Dennis L. 
Published: March 2007

AbstractThe “forward” method of an optimal gradient coil design provides a coil that has the minimal cost function value. It is shown in this study that the solution obtained by minimizing the cost function is directly dependent on the specified cost function and generally results in a deviation from the most desirable coil design. In this paper, a gradient coil design approach for obtaining the best achievable coil performance for pre‐determined imaging applications is presented. Through this approach, all intermediate coil performance values calculated during an optimization process, using a simulated annealing algorithm, are stored and presented in a three‐dimensional data set. Using this three‐dimensional data set, a coil designer is able to make a balance between different coil performance parameters and to select a coil that is the most desirable for the pre‐determined imaging applications.
Single‐shot halfk‐space high‐resolution gradient‐recalled EPI for fMRI at 3 tesla
Authors: Jesmanowicz Andrzej , Bandettini Peter A. , Hyde James S. 
Published: March 2007

AbstractHalfk‐space gradient‐recalled echo‐planar imaging (GR‐EPI) is discussed in detail.T2* decay during fullk‐space GR‐EPI gives rise to unequal weighting of the lines ofk‐space, loss of signal intensity at the center ofk‐space, and a point‐spread function that limits resolution. In addition, the long readout time for high‐resolution fullk‐space acquisition gives rise to severe susceptibility effects. These problems are substan tially reduced by acquiring only half ofk‐space and filling the empty side by Hermitian conjugate formation. Details of the pulse sequence and image reconstruction are presented. The point‐spread function is 3½times narrower for half than fullk‐space acquisition. Experiments as well as theoretical con siderations were carried out in a context of fMRI using a whole‐brain local gradient and an RF coil at 3 Tesla. Using a bandwidth of ±83 kHz, well‐resolved single‐shot images of the human brain, as well as good quality fMRl data sets were obtained with a matrix of 192 × 192 over 16 × 16 cm2FOV using halfk‐space techniques. The combination of high spa tial resolution using the methods presented in this article and the high temporal resolution of EPI opens opportunities for research into fMRl contrast mechanisms. Increase of percent signal change as the resolution increases is attributed to reduction of partial volume effects of activated voxels. Histo grams of fMRl pixel responses are progressively weighted to higher percent signal changes as the resolution increases. The conclusion has been reached that halfk‐space GR‐EPI is generally superior to fullk‐space GR‐EPI and should be used even for low‐resolution (64 × 64) EPI.
Automated spectral analysis II: Application of wavelet shrinkage for characterization of non‐parameterized signals
Authors: Young Karl , Soher Brian J. , Maudsley Andrew A. 
Published: March 2007

AbstractAn iterative method for differentiating between known resonances and uncharacterized baseline contributions in MR spectra is described. The method alternates parametric modeling, using a priori knowledge of spectral parameters, with non‐parametric characterization of remaining signal components, using wavelet shrinkage and denoising. Rapid convergence of the iterative method is demonstrated, and examples are shown for analysis of simulated data and an in vivo 1H spectrum from the brain. Results show good separation between metabolite signals and strong baseline contributions.
High‐accuracy MR tracking of interventional devices: The overhauser marker enhancement (OMEN) technique
Authors: Joensuu Raimo P. , Sepponen Raimo E. , Lamminen Antti E. , Savolainen Sauli E. , Standertskjöld‐Nordenstarn Carl‐Gustaf M. 
Published: March 2007

AbstractA new technique for visualization of interventional devices in magnetic resonance imaging is presented. Determination of the position of an invasive device is made possible by incorporating into the device a small marker that emits the NMR signal. This signal is enhanced by the use of the Overhauser phenomenon. This technique differs from the earlier reported techniques for marking interventional instruments in the sense that the contrast between the marker and tissue is not based on different relaxation rates, but on NMR signal enhancement. A prototype marker was constructed and inserted into an inductively fed loop‐gap resonator that couples saturation energy with the marker. Circuit analogies are presented that model the Overhauser phenomenon and the coupling circuit. In vifm experiments demonstrated that the marker is visible in MR images up to a slice thickness of 50 mm when inserted in excised animal liver and fat tissues.
Capillary transfer constant of Gd‐DTPA in the myocardium at rest and during vasodilation assessed by MRI
Authors: Fritz‐Hansen Thomas , Rostrup Egill , Sørndergaard Lars , Ring Pod B. , Amtorp Ole , Larsson Henrik B. W. 
Published: March 2007

AbstractThe purpose of this study was to determine whether the capillary transfer constant (Ki) of gadolinium‐DTPA was sensitive to perfusion changes and whether ischemic regions in the myocardium could be identified using the modified Kety formula. Ki was measured at rest and during dipyridamole‐induced vasodilation in 10 healthy volunteers and in 10 patients with ischemic heart disease. Ki increased by a factor of 2.5 ± 1.2 (mean ± SD) from 55 ± 16 ml 100 g−1min−1 at rest to 136 ± 46 ml 100 9−1min−1 (P < 0.01) during vasodilation in the healthy subjects. In the patients, there were no changes in Ki during vasodilation in ischemic regions (50 ± 18 versus 49 ± 30 ml 100 g−1min−1 (P > 04)). Ki increased in nonischemic regions by a factor of 2.0 ± 0.8 from 44 ± 17 to 81 ± 32 ml 100 g−1min−1 during vasodilation (P < 0.02). It is concluded that the capillary transfer constant is sensitive to perfusion changes and that regional ischemia can be detected with MRI. This noninvasive and quantitative method may prove useful in the evaluation of patients with ischemic heart disease.
Single‐shot, motion insensitive cardiac imaging on a standard clinical system
Authors: Meyerand M. Elizabeth , Moritz Chad H. , Wong Eric C. 
Published: March 2007

AbstractThe overall goal of this study was the development and application of a less motion sensitive, single‐shot MRI technique for use on a standard clinical system in a dynamic imaging setting, such as cardiac scanning. Time encoding, a single‐shot line scanning technique, has been used to produce single‐shot, small field‐of‐view cardiac images without the use of presaturation pulses. The major advantages of this method are: (1) as a line scanning technique, time encoding is minimally sensitive to motion when compared with 2D Fourier methods, and (2) aliasing will not occur if the object being imaged extends beyond the field of view.
Lightweight electromagnetic shields using optimized polyaniline composites in the microwave band
Authors: Hoang N. H. , Wojkiewicz J.‐L. , Miane J.‐L. , Biscarro R. S. 
Published: March 2007

AbstractA genetic algorithm (GA) was used to optimize a multilayer electromagnetic shield of polyaniline (PANI)–polyurethane (PU) conducting composites in the microwave band. First, the electronic properties of freestanding films with different mass fractions of polyaniline were studied. A very low percolation threshold (0.2%) was found, with a maximum of conductivity of 104 S/m. Second, the electromagnetic shielding effectiveness of the films were investigated in the X and Ku bands (8.2–18 GHz), showing an attenuation increase of 1–40 dB with the mass fraction of polyaniline in the blends. Then, the electromagnetic shielding properties of multi‐layered PAni–PU composites were investigated in order to obtain an attenuation superior to 40 or 80 dB, depending on the application. To improve the performances of the electromagnetic shields, three‐layered PAni–PU composites were made, using an optimization method. The intrinsic physical parameters of the composites were used as a database for the optimization calculation. The optimization results showed that materials with a thickness of <500 µm could answer many industrial or military shielding applications. As the electronic properties can be tuned easily with the mass fraction of polyaniline in the blends, conducting multi‐layered composite materials can be made following the results of the optimization. Their electromagnetic shielding effectiveness was measured, showing good agreement between the measurements and modeling. These results demonstrated that the genetic algorithm allows us to conceive lightweight and high performance electromagnetic shields using intrinsically conducting polymers. The mass per unit of surface of the shield was <200 g/m2, giving potential applications in the aeronautics domain. Copyright © 2007 John Wiley & Sons, Ltd.
Blood cell separation using crosslinkable copolymers containing N,N‐dimethylacrylamide
Authors: Natori Shizue Hayashi , Kurita Keisuke 
Published: March 2007

AbstractAmphiphilic copolymers using hydrophilic N,N‐dimethylacrylamide (DMA), hydrophobic methyl methacrylate (MMA) and a crosslinkable monomer, 3‐methacryloyloxypropyl trimethoxysilane (MTSi), were synthesized and evaluated as coating materials for leukocyte removal filters for whole blood. When filters composed of non‐woven fabrics were coated with crosslinked synthesized copolymers, the elution ratios of the copolymers to water were adequately low because of the crosslinking with trimethoxysilane groups of MTSi units in the copolymers. Filters coated with crosslinked poly(DMA‐co‐MTSi) having a 0.96 mole fraction of DMA units showed a 0.35 ± 0.44% platelet permeation ratio and a logarithmic reduction of 4.0 ± 0.68 for leukocytes. On the other hand, an increase in the content of MMA units in the DMA‐containing copolymers improved the permeation ratio of the platelets dramatically. Filters coated with crosslinked poly(DMA‐co‐MMA‐co‐MTSi) containing a 0.39 mole fraction of MMA units and a 0.58 mole fraction of DMA units showed an 86 ± 3.0% platelet permeation ratio and a logarithmic reduction of 2.1 ± 1.2 for leukocytes. This indicates that an adequate content of hydrophobic monomer units, such as MMA units, is necessary for effective platelet permeation. Copyright © 2007 John Wiley & Sons, Ltd.
Preparation, characterization and tableting properties of two new pachyman‐based pharmaceutical aids: I. disintegrants in dispersible tablets
Authors: Xiao Yuling , Liang Shucai , Qiu Guofu , Wu Jianyuan , Zhang Junbo , Hu Xianming 
Published: March 2007

AbstractLinear pachyman was isolated from the sclerotium of Poria cocos. Its hydroxypropyl and carboxymethyl derivatives, with considerable hydrophilicities, were synthesized. Their chemical structures, biocompatibilities, powder and tableting properties were determined. To exploit their novel applications in tablet excipients, ampicillin and probenecid dispersible tablets were compressed using the two derivatives as disintegrants, respectively. The detailed characterization of the tablets indicated the great potential of the two synthesized derivatives to be used as pharmaceutical excipients. Copyright © 2007 John Wiley & Sons, Ltd.
The reduction of oxidative stress, anticoagulation of platelets, and inhibition of lipopolysaccharide by conjugated linoleic acid bonded on a polysulfone membrane
Authors: Kung Fu‐Chen , Chang Jung‐Jhih , Yang Ming‐Chien 
Published: March 2007

AbstractConjugated linoleic acid (CLA) was covalently bonded onto the surface of a polysulfone (PSF) membrane via esterification. The surface was characterized with contact angle measurement and FT‐IR spectrometery. The capability of bonded CLA on the suppression of oxidative stress was evaluated. The level of reactive oxygen species (ROS) was measured by the chemiluminescence (CL) method to evaluate the oxidative stress. Furthermore, the removal of bacterial endotoxin (lipopolysaccharide, LPS) by CLA‐bonding PSF was measured with enzyme‐linked immunosorbent assay (ELISA). The reduction in the platelet adhesion on the PSF surface was evaluated using a SF‐3000 automated hematology analyzer. The result indicates that CLA‐bonding PSF can reduce the adhesion of platelets by 73%. The concentration of LPS can be reduced by CLA‐bonding PSF 1.6 times more than unmodified PSF membrane. In addition, the level of ROS against CLA‐bonding PSF membrane was 23% of that against unmodified PSF membrane. Therefore CLA‐bonding PSF membrane could offer protection for patients against oxidative stress and could also inhibit LPS for clinical applications. Copyright © 2007 John Wiley & Sons, Ltd.
Nitroxide mediated living radical polymerization of styrene onto poly (vinyl chloride)
Authors: Abbasian Mojtaba , Entezami Ali Akbar 
Published: March 2007

AbstractNitroxide‐mediated ‘living’ free radical polymerisation (LREP) was employed for the first time to prepare graft copolymer by having arylated poly (vinyl chloride) (PVC‐Ph) as a backbone and polystyrene (PS) as branches. The graft copolymerization of styrene was initiated by arylated PVC carrying 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO) groups as a macroinitiator. Thus, the arylated PVC was prepared in the mild conditions and these reaction conditions could overcome the problem of gelation and crosslinking in polymers. Then, 1‐hydroxy TEMPO was synthesized by the reduction of TEMPO with sodium ascorbate. This functional nitroxyl compound was coupled with brominated arylated PVC (PVC‐Ph‐Br). The resulting macro‐initiator (PVC‐Ph‐TEMPO) for ‘living’ free radical polymerization was then heated in the presence of styrene to form graft copolymer. DSC, GPC, 1HNMR, and FT‐IR spectroscopy were employed to investigate the structure of the polymers. Copyright © 2007 John Wiley & Sons, Ltd.
Synthesis of well‐designed polymers carrying saccharide moieties via RAFT miniemulsion polymerization
Authors: Al‐Bagoury Mohamed , Buchholz Klaus , Yaacoub Emile‐Joseph 
Published: March 2007

AbstractTwo hydrophobic vinyl saccharide monomers based on D‐glucose and D‐fructose were polymerized by employing the reversible addition‐fragmentation transfer (RAFT) miniemulsion polymerization technique to prepare well‐designed glycopolymers. Three dithiobenzoate‐RAFT agents [SC(Ph)SR], 1‐phenylethyl dithiobenzoate (PED), 2‐phenylprop‐2‐yl dithiobenzoate (PPD), and 2‐cyanoprop‐2‐yl dithiobenzoate (CPD), were used to control the growth of polymer chains. The best results were obtained in the presence of the PPD‐RAFT agent and the formed polymers have polydispersity index's (PDI) lower than 1.15. Under adequate miniemulsion polymerization conditions, a glycopolymer with PDI of 1.1 and molecular weight of 5 × 104 g/mol has been successfully synthesized in a short reaction time of 100 min. Furthermore, some block copolymers containing saccharide segment with butyl or methyl methacrylate were prepared. Copyright © 2007 John Wiley & Sons, Ltd.