bluuebunny/crossref_metadata_2025 huggingface dataset:
On the behaviour of the elongational viscosity of a nematic polymer in elongational flow
Authors: Diogo A. C.
Published: March 2011

For nematic materials, the elongational viscosity depends on the orientation of the director field relative to the velocity field. A computation of the elongational viscosity for various flow geometries is presented. It is shown that for uniaxial elongational flow the director aligns along the flow direction with a characteristic time τE = −2γ1/(3γ2ϵ); for planar elongational flow, the director aligns perpendicular to the flow with a characteristic time τE2 = ‐γ1/(γ2ϵ).
Stress‐strain behavior of polyacrylamide networks
Authors: Baselga J. , Piérola I. F. , Hernández‐fuentes I. , Llorente M. A.
Published: March 2011

The mechanical properties of a number of polyacrylamide gels have been studied by means of elastic measurements in elongation. Different gels were prepared by varying the proportions of both comonomers, acrylamide and N, N‐methylene‐bisacrylamide which is used as crosslinker, and a very broad range of concentrations was covered. The most important results considered were the elastic phantom modulus, the degree of (equilibrium) swelling and the elongation at rupture. The data were interpreted in terms of the mechanism of the gelation process taking into account a number of parameters that affect the final structure of the gels: comonomer reactivities, sequence length distributions and cycles formation. Consideration of these factors can explain properly all the features of the elastic results as well as some other properties related to the gelation process such as gel point data.
Analysis of enthalpy relaxation in amorphous poly(ethylene terephthalate)
Authors: Montserrat S. , Cortks P.
Published: March 2011

Endothermic peaks below or superposed to Tg have been observed by Differential Scanning Calorimetry in samples of amorphous poly(ethy1ene terephthalate) (PET) which were submitted to a wide range of annealing conditions. These endothermic peaks allow the obtention of the excess of enthalpy (6) and subsequently the effective relaxation times T(eff) On applying an empirical equation of T∼∼, with separate contribution of temperature and structure (6), kinetic parameters have been found in a range close to Tg, resulting for PET an apparent activation energy of 860.5 kJ/mol (between 60 and 68OC). This parameter has been also calculated from de dependence of Tg with the heating rate in a DSC scan and the values found are between 314 and 419 kJ/moL
Study of the molecular origin of the mechanical and dielectric β relaxation of methyl methacrylate/isopropenyl methyl ketone copolymers
Authors: Ribes‐Greus A. , Soria V. , Figueruelo J. E. , Díaz‐calleja R.
Published: March 2011

A study of the β relaxation in a series of methyl methacrylate and isopropenyl methyl ketone copolymers by dielectric, mechanical and thermally stimulated current methods has been carried out. It is observed that the position on the axis of temperature and height of the β relaxation is nearly the same in all the pure polymer and in the two copolymers. This points out that the molecular origin of the β relaxation is related to the partial rotation of the alkoxycarbonyl group in the side chains. However, the apparent activation energy of the β relaxation seems to have a smooth energy distribution, which we have associated with the intermolecular barrier that opposes to this relaxation.
Mechanical properties of two interpenetrating networks
Authors: Poussin D. , Lataillade J. L. , Pouyet J.
Published: March 2011

Interpenetration of polyepoxide, polyurethane and polyester networks leads to matrix for high performance composites. The increase of ultimated elongation, shock resistance is due to a mechanical homogeneization, because of a better stereometric organization. On the other hand, it seems that this does not contribute to the rubber plateau behaviour, the molecular mass between crosslinks and the glassy transition.
Dynamic mechanical behaviour of a polysulfone in the glass transition region
Authors: Macho E. , Alberdi J. M. , Alegría A. , Colmenero J.
Published: March 2011

Dynamic mechanical measurements on commercial samples of a polysulfone have been performed at different frequencies at a temperature range from 400 to 510 K. Bending mode measurements were carried out in a Standard Polymer Laboratories DMTA apparatus, which simultaneously delivers both real and imaginary components of Young's complex modulus. Two main dispersion regions are apparent in the relaxation spectrum, the mechanical α‐relaxation, located at temperatures just above the calorimetric glass‐transition, and the high temperature dispersion process, which is related to the behaviour of the entanglement network. Master curves have been built from the experimental data. Shift factors corresponding to the two dispersion processes have been well fitted by only one Vogel‐Fulcher law. Below Tg, shift factor deviates towards an Arrhenius‐like behaviour which has been associated to a low strength sub‐Tg relaxation. Master curves allow the shape parameters of the two main dispersion processes to be calculated. Values obtained indicate that the dispersion process associated to the glass transition arises from a relatively high‐coupled intra‐cluster molecular motion with a nearly random cluster size distribution. However, the high temperature (low frequency) dispersion process seems to arise from the motion of units with weaker coupling.
On the microhardness of irradiated polycarbonate
Authors: Bajpai R. , Keller J. M. , Datt S. C.
Published: March 2011

Polycarbonate specimens were irradiated with gamma irradiation doses ranging from 2–75 Mrad. Vickers hardness number (Hv) of these specimens has been calculated. It has been found that Hv decreases with irradiation dose upto 50 Mrad and thereafter it suddenly increases at 75 Mrad. This variation of Hv with gamma irradiation has been explained on the basis of scissioning and crosslinking in polymers.
Microhardness measurement of polypropylene, poly(ethylene terephthalate) and poly(tetra‐fluoroethylene)
Authors: Parashar P. , Bajpai R. , Keller J. M. , Datt S. C.
Published: March 2011

Microhardness studies of commercially available polypropylene, poly(ethylene terephthalate) and poly(tetrafluoroethylene) have been carried out to investigate the effect of load on Vickers hardness number. The nature of the polymers have also been explained on the basis of the logarithmic index n and small stress behaviour with the help of Newtonian resistance pressure.
The use of subcomponents for the prediction of the mechanical behaviour of polypropylene injection moulded products
Authors: Cunha A. M. , Pouzada A. S. , Oliveira M. J. , Crawford R. J.
Published: March 2011

The mechanical performance of injection moulded products is strongly dependent on the processing conditions due mainly to the way in which these affect the microstructure of the moulded material. This paper presents a new approach to this problem whereby the mechanical behaviour is predicted using data obtained from subcomponents, such as discs. These were moulded in polypropylene using different gate types and moulding conditions (injection rate and mould temperature). The microstructure of the subcomponents was examined by polarized light microscopy to assess the average size of the spherulites and the skin/wall thickness ratio. These were then related to the mechanical properties of the subcomponents as characterized by a three point bending test and by an instrumented tensile impact test. The paper presents the data obtained and describes the correlation between processing structure and mechanical behaviour. The value of this subcomponent approach is illustrated through its application to some commercial mouldings.
The relationship between processing conditions, morphological structure and mechanical properties of knit lines of an injection molded semi‐crystalline thermoplastic
Authors: Singh D. , Moslé H. G.
Published: March 2011

The structure‐property relationship of injection molded polypropylene samples with knit lines was investigated. Double gated tensile bars were injection molded under different molding conditions in order to study the influence of molding parameters on crystallinity and spherulite diameter. It was observed that the degree of crystallinity and spherulite size were highly dependent on cooling rate. To improve weld line strength and elastic modulus, an increase in crystalline fraction and the diameter of the crystalline aggregates seems to be necessary.
A kinetic model for network formation in free radical polymerization
Authors: Tobita H. , Hamielec A. E.
Published: March 2011

A new model for gelation in free radical polymerization based on the pseudo‐kinetic rate constant method is proposed. This model which considers all of the important reactions in free radical polymerization can be used to make calculations of the average properties during network formation. The model is more general than the statistical model based on Flory/Stockmayer treelike concepts and under special limiting conditions reduces to the Flory/Stockmayer model. The present model is easy to use and provides greater insight into the phenomenon of gelation and growth and structure of crosslinked polymers synthesized by free radical polymerization.
The role of the cosurfactant in the miniemulsion copolymerization of vinyl acetate and n‐butyl acrylate
Authors: Delgado J. , El‐Aasser M. S. , Silebi C. A. , Vanderhoff J. W.
Published: March 2011

The role of the cosurfactant in the miniemulsion copolymerization process of 50:50 molar ratio vinyl acetate/n‐butyl acrylate miniemulsion copolymerization is analyzed. The mixed emulsifier system used to prepare the miniemulsions was sodium hexadecyl sulfate as surfactant and hexadecane as cosurfactant. It is shown that even though hexadecane plays an important role in the distribution of the monomers between the different phases present during the copolymerization process, it does not greatly affect the kinetics. It is the presence of stable submicron droplets what really alters the kinetics by shifting the particle nucleation mechanism from the aqueous phase to the monomer droplets.
Charge carrier transport in polymers: A view by thermally stimulated currents
Authors: Zieliński Marek , Plans Joaquin
Published: March 2011

Thermally Stimulated Currents (TSC) technique is widely used to study electronic properties of polymers. In this paper we will sketch the history of how this technique was applied to look at basic phenomena in electrical conduction: generation and transport of charge carriers, electrons and holes. We will also discuss the latest developments in the analysis of the TSC spectra, including the transport and release peaks.
Thermally stimulated and isothermal discharges of corona‐charged polypropylene
Authors: Singh Ranjit , Keller J. M. , Datt S. C.
Published: March 2011

Detailed investigation of short‐ and open‐circuit thermally stimulated currents (TSC's) along with that of isothermal charge decay and absorption currents have been made on corona‐charged 40 μm thick commercial‐grade polypropylene (PP) foils. Comparison of two types of TSC's revealed that the polymer is characterized by energetically deep surface traps giving rise to a 145°C peak in open‐circuit TSC's. However, the other three peaks occurring at temperatures below 145°C in both types of TSC's are concluded to be due to bulk traps. The observed anomalous TSC's flowing in the same direction as the charging current at higher values of polarizing field and temperature have been considered to be due to space‐charge injection assisted by localized states and the blocking nature of the electrodes. The equivalence between TSC and discharge techniques has been established.
Etude comparative de la conductivite dans des films et des plaquettes de polymeres electroactifs (PPS et PPP) dopes par implantation ionique
Authors: Moliton A. , Duroux J. L. , Ratier B. , Froyer G. , Pelous Y.
Published: March 2011

In our laboratory, we have studied in a systematic way, ion effect on the conductivity of the polyparaphenylene (PPP) versus implantation parameters. In a first time, we have made a basic study on PPP pallets, and then compared these results with the other ones obtained with PPP and PPS (polyphenylene sulfide) films.
Conducting injection moulded carbon black filled polyethylene
Authors: Baltá calleja F. J. , Bayer R. K. , Ezquerra T. A. , Salazar Martinez J. , Zachmann H. G.
Published: March 2011

Carbon black filled polyethylenes were prepared by injection moulding using a mould which induces elongational flow. In case of high molecular weight matrices, a microadditive segregation within the material leads to conductivity values σ ≈ 10−1 ω−1 cm−1 which are much larger than those obtained for the compression moulded material. The use of lower molecular weight matrices leads to lower conductivity levels. This is attributed to a less pronounced destruction of carbon black agglomerates during the mixing process and to an orientation effect of these particles by injection flow.
Recent developments in the synthesis and functionalization of conducting poly(thiophenes)
Authors: Roncali Jean , Garreau Robert , Delabouglise Didier , Garnier Francis , Lemaire Marc
Published: March 2011

The mechanism of the electropolymerization of thiophene derivatives has been investigated by varying the electrosynthesis conditions and the monomer structure. The results of these analyses led to the definition of optimized electrosynthesis conditions allowing the control of the electrical and electrochemical properties of poly(thiophenes). On the basis of these results, the properties of these polymers have been modified by means of a new one‐step electrosynthesis of conducting composite materials and by the direct electropolymerization of tailor‐made functionalized monomers. For this purpose, the steric conditions associated to the various possibilities of covalent derivatization have been analyzed, leading to the definition of a “functionalization space”, compatible with the preservation of high conductivity and electrochemical reversibility in the resulting polymers. This concept has been applied to the synthesis of highly conducting chiral poly(thiophenes) on which an effect of enantioselective molecular recognition has been demonstrated for the first time.
Modification of poly(N‐vinylcarbazole): Nitration and thermally stimulated depolarization current study
Authors: Zamora Fernando , Del Carmen Gonzalez Maria , Del Val Juan José
Published: March 2011

In order to introduce some electronic affinity in poly(N‐vinylcarbazole), we proceeded to incorporate NO2 groups in its pendant aromatic group. Two samples obtained by different polymerization processes were chosen: a commercial sample LUVICAN (BASF) and a cationically polymerized one. Both samples were fractionated and characterized by GPC and viscometry. The first ones were treated with a sulphuric acid‐nitric acid mixture, while the second ones were nitrated in presence of dimethyl sulphoxide. The glass transition temperature and the corresponding dielectric α relaxation were studied by differential scanning calorimetry and thermally stimulated currents techniques, respectively. Rigidity of the macromolecular chain and the degree of nitration lead to different behaviour in the relaxation process.
EPR parameters of radical ions and polarizability effect
Authors: Egorochkin Alexey N. , Kuznetsova Olga V. , Khamaletdinova Nadiya M. , Domratcheva‐Lvova Lada G.
Published: March 2011

The literature data on substituent influence on the g factors, hyperfine coupling (hfc) constants (a) of the EPR signals and the spin densities (ρ) have been analyzed for 25 series of the organic radical cations and radical anions as well as of the transition metal complexes. The g, a, and ρ values were first established to depend not only on the inductive and resonance effects but also on the polarizability of substituents which can be characterized by the σα constants. The polarizability effect is caused by the partial charge on the radical center. This effect consists in an electrostatic attraction between the charge and the dipole moments induced by this charge in the substituents. The polarizability contribution ranges up to 92%. Copyright © 2011 John Wiley & Sons, Ltd.
Experimental and computational studies of nJ(77Se,1H) selenium–proton couplings in selenoglycosides
Authors: Kövér Katalin E. , Kumar Ambati Ashok , Rusakov Yury Yu. , Krivdin Leonid B. , Illyés Tünde‐Zita , Szilágyi László
Published: March 2011

Selenoglycosides are important starting materials in synthetic carbohydrate chemistry and play a role in biological interactions as well. Both aspects are influenced by the conformation around the glycosidic bond. Here, we present a combined experimental and computational approach to measure and evaluate nJ(77Se,1H) coupling constants for their use in conformational analysis. The measurements were carried out using a modified CPMG‐HSQMBC pulse scheme which yields pure absorption antiphase multiplets to allow accurate determination of the nJXH values regardless of the size of the proton‐proton couplings. Theoretical calculations were performed at the Second‐Order Polarization Propagator Approach (SOPPA) level. Population‐averaged values calculated for geminal and vicinal couplings are in a good agreement with experiment indicating an adequate theoretical level of the calculations. Experimental observations and computations alike have indicated that two‐bond 77Se‐1H couplings, 2J(77Se,1H), in a H1‐C1‐Se‐X moiety are very sensitive to the torsion angle around the C1‐Se‐bond and will, therefore, be useful for conformational studies. Copyright © 2011 John Wiley & Sons, Ltd.
Resolution of a nonionic surfactant oligomeric mixture by means of DOSY with inverse micelle assistance
Authors: Asaro Fioretta , Savko Nina
Published: March 2011

DOSY is a recognized, efficient technique in the analysis of mixtures. It relies on the differences in self‐diffusion coefficients, which are determined by the molecular size. Nowadays, efforts are directed towards devising matrices able to interact with the components of the mixture with differential affinity, and therefore capable to interfere with the diffusion processes and to display resolving power towards species of close, or even equal molecular weight, like isomers. Usually, commercial nonionic surfactants are mixtures of oligomeric species, since the head group, which is a short polyoxyehtylene chain, is somewhat polydisperse. The embedment of Igepal CA‐520, 5 polyoxyethylene iso‐octylphenyl ether, in an inverse microemulsion led to the separation of 1H signals of the various oligomeric components. This ensued from the differential partitioning between the oil and the surface of the inverse micelles, which depends on the ethyleneoxide number (EON) of the head groups. Thus, it was possible to ascertain that the length distribution of the polyethyleneoxide chains is ingood agreement with the Poisson distribution theoretically predicted for the polymerization of ethylene oxide. The DOSY spectrum contributed to the assignment of the signals and afforded the partition degree, between the two environments, for each individual oligomeric species, providing further insight into nonionic inverse microemulsions, at present widely employed reaction media in the nanotechnological syntheses. Copyright © 2011 John Wiley & Sons, Ltd.
Rapid acquisition of 1H and 19F NMR experiments for direct and competition ligand‐based screening
Authors: Dalvit Claudio , Gossert Alvar D. , Coutant Jérôme , Piotto Martial
Published: March 2011

Direct and competition ligand‐based NMR experiments are often used in the screening of chemical fragment libraries against a protein target due to the high relative sensitivity of NMR for protein‐binding events. A plethora of NMR methods has been proposed for this purpose. Two of these techniques are the 19F T2 filter and the 1H selective T2 filter experiments. Modifications of the pulse sequences of these experiments have resulted in a ∼2‐fold reduction in the experiment time thus allowing an increase in the screening throughput and making NMR an attractive technique for screening large compound collections. Copyright © 2011 John Wiley & Sons, Ltd.
Dynamic 1H NMR study around the carbon–carbon single bond and partial carbon–carbon double bond in the two particular phosphorus ylides and in an enaminoester
Authors: Habibi‐Khorassani Sayyed Mostafa , Ebrahimi Ali , Maghsoodlou Malek Taher , Same‐Salari Sara , Nasiri Shahin , Ghasempour Hojjat
Published: March 2011

Herein, a series of separate dynamic 1H NMR effects are reported at different temperatures within a particular enaminoester involving a phenanthridine. These effects are attributed to restricted rotation around the two single bonds such as carbon–carbon (HaCCHb) and nitrogen–carbon (NCCOOCH3). Activation energies (Ea) for these interconversion processes in their rotational isomers are equal to 20 and 20 ± 1 kJ mol−1, respectively. In addition, three dynamic 1H NMR effects are investigated at different temperatures for a particular phosphorus ylide involving a 2‐indolinone around the carbon–carbon single bond (HCCPPh3) within the two Z‐ and E‐rotational isomers and partial carbon–carbon double bond (OCH3‐CC‐PPh3). Activation energies (Ea) for these interconversion processes in rotational isomers are equal to 53, 63 and 73 ± 1 kJ mol−1, respectively. This behavior was also observed for other phosphorus ylide containing 2‐mercaptobenzoxazole around the carbon–carbon single bond and partial carbon–carbon double bond with their relevant activation energies containing 13, 10 and 75 ± 1 kJ mol−1, respectively. Copyright © 2011 John Wiley & Sons, Ltd.
Application of fluorine NMR for structure identification of steroids
Authors: Ampt Kirsten A. M. , Aspers Ruud L. E. G. , Jaeger Martin , Geutjes Pepijn E. T. J. , Honing Maarten , Wijmenga Sybren S.
Published: March 2011

Fluorinated steroids were examined using 1D and 2D homo‐ and heteronuclear 19F NMR, such as 19F1H and 19F13C. The utilization of fluorine NMR accounted for spectral simplification and resulted in a straightforward pathway for the determination of structures including the configuration of these compounds; these steroids present an illustrative example for other types of fluorinated compounds, which are increasingly encountered in drug discovery. The potential of 19F NMR is elaborated on in detail for two compounds containing diastereotopic fluorines with different coupling patterns. The analysis of the coupling patterns and the through‐space interactions resulted in the determination of the structure and configuration. Heteronuclear correlation experiments, i.e. 19F1H HETCOR, 19F13C HMQC and HMBC, and 19F1H HOESY, were applied to determine first the relative stereochemistry and then the molecular configuration at C4 and C5 of a steroidal compound bearing a fused three‐membered ring with two fluorine substituents. These examples proved 19F NMR to be a useful addition to the extensively used 1H and 13C NMR within structure elucidation and configuration determination of small molecules. Copyright © 2011 John Wiley & Sons, Ltd.
From CCSD(T)/aug‐cc‐pVTZ‐J to CCSD(T) complete basis set limit isotropic nuclear magnetic shieldings via affordable DFT/CBS calculations
Authors: Kupka Teobald , Stachów Michał , Nieradka Marzena , Kaminsky Jakub , Pluta Tadeusz , Sauer Stephan P. A.
Published: March 2011

It is shown that a linear correlation exists between nuclear shielding constants for nine small inorganic and organic molecules (N2, CO, CO2, NH3, CH4, C2H2, C2H4, C2H6 and C6H6) calculated with 47 methods (42 DFT methods, RHF, MP2, SOPPA, SOPPA(CCSD), CCSD(T)) and the aug‐cc‐pVTZ‐J basis set and corresponding complete basis set results, estimated from calculations with the family of polarization‐consistent pcS‐n basis sets. This implies that the remaining basis set error of the aug‐cc‐pVTZ‐J basis set is very similar in DFT and CCSD(T) calculations. As the aug‐cc‐pVTZ‐J basis set is significantly smaller, CCSD(T)/aug‐cc‐pVTZ‐J calculations allow in combination with affordable DFT/pcS‐n complete basis set calculations the prediction of nuclear shieldings at the CCSD(T) level of nearly similar accuracy as those, obtained by fitting results obtained from computationally demanding pcS‐n calculations at the CCSD(T) limit. A significant saving of computational efforts can thus be achieved by scaling inexpensive CCSD(T)/aug‐cc‐pVTZ‐J calculations of nuclear isotropic shieldings with affordable DFT complete basis set limit corrections. Copyright © 2011 John Wiley & Sons, Ltd.
On the mechanisms enabling myocardial edema contrast in bSSFP‐based imaging approaches
Authors: Zhou Xiangzhi , Rundell Veronica , Liu Ying , Tang Richard , Shah Saurabh , Zuehlsdorff Sven , Li Debiao , Dharmakumar Rohan
Published: March 2011

The biophysical mechanisms influencing balanced steady‐state free precession (bSSFP) based edema imaging in the setting of acute myocardial infarction are not well understood. To assess the various mechanisms that enable the detection of myocardial edema on bSSFP‐based imaging approaches (cine bSSFP and T2‐prepared bSSFP), experiments were conducted in canine models subjected to ischemia‐reperfusion injury. Results showed that in addition to relaxation effects, the alteration in thermal equilibrium (M0) (including magnetization transfer) has a significant contribution to the image contrast between edematous and healthy myocardium. The relative signal‐intensity ratios between edematous and healthy myocardium were: 1.51 ± 0.18 (cine bSSFP) and 1.58 ± 0.20 (T2‐prepared bSSFP); the theoretically estimated relative relaxation and M0 effects were: 1.17 ± 0.09 and 1.30 ± 0.19, respectively (cine bSSFP), and 1.49 ± 0.23 and 1.06 ± 0.07, respectively (T2‐prepared bSSFP). There were no significant difference between cine bSSFP and T2‐prep bSSFP relative signal‐intensity ratios. However, the relative relaxation effect in cine bSSFP was significantly lower than in T2‐prep bSSFP (P < 0.05), and the M0 effect in cine bSSFP was significantly higher than in T2‐prep bSSFP (P < 0.05). Hence the acquisition strategies that wish to maximize myocardial edema contrast in cine bSSFP imaging should take both relaxation and M0 effects into account. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.
Assessment of tissue edema in patients with acute myocardial infarction by computer‐assisted quantification of triple inversion recovery prepared MRI of the myocardium
Authors: Johnstone R. I. , Greenwood J. P. , Biglands J. D. , Plein S. , Ridgway J. P. , Radjenovic A.
Published: March 2011

The aim of this study was to design a computer algorithm to assess the extent of cardiac edema from triple inversion recovery MR images of the human left ventricular myocardium. Twenty‐one patients presenting with acute myocardial infarction were scanned within 48 h of the onset of symptoms. Eight patients were scanned a second time, 4 weeks after the initial event. Myocardial edema was detected in 27 of 29 studies using visual contour‐based manual segmentation. A reference standard, created from the segmentations of three raters by voxel‐wise majority voting, was compared to the edema mass estimates obtained using a newly developed computer algorithm. At baseline (n = 20), the reference standard yielded an edema mass of 16.4 ± 15.0 g (mean ± SD) and the computer algorithm edema mass was 16.4 ± 12.6 g. At follow‐up (n = 7), the reference standard edema mass was 7.1 ± 4.4 g compared to 16.3 ± 7.7 g at baseline. Computer algorithm estimates showed the same pattern of change with 5.7 ± 5.7 g at follow‐up compared to 20.8 ± 13.8 g at baseline. Although there was a significant degree of discrepancy between reference standard and computer algorithm estimates of edema mass in individual patients, their overall agreement was good, with intraclass correlation coefficient ICC(3, 1) = 0.753. Magn Reson Med, 2010. © 2011 Wiley‐Liss, Inc.
Extended graphical model for analysis of dynamic contrast‐enhanced MRI
Authors: Chen Huijun , Li Feiyu , Zhao Xihai , Yuan Chun , Rutt Brian , Kerwin William S.
Published: March 2011

Kinetic analysis with mathematical models has become increasingly important to quantify physiological parameters in computed tomography (CT), positron emission tomography (PET), and dynamic contrast‐enhanced MRI (DCE‐MRI). The modified Kety/Tofts model and the graphical (Patlak) model have been widely applied to DCE‐MRI results in disease processes such as cancer, inflammation, and ischemia. In this article, an intermediate model between the modified Kety/Tofts and Patlak models is derived from a mathematical expansion of the modified Kety/Tofts model. Simulations and an in vivo experiment involving DCE‐MRI of carotid atherosclerosis were used to compare the new extended graphical model with the modified Kety/Tofts model and the Patlak model. In our simulated circumstances and the carotid artery application, we found that the extended graphical model exhibited lower noise sensitivity and provided more accurate estimates of the volume transfer constant (Ktrans) and fractional plasma volume (vp) than the modified Kety/Tofts model for DCE‐MRI acquisitions of total duration less than 100–300 s, depending on kinetic parameters. In comparison with the Patlak model, we found that the extended graphical model exhibited 74.4–99.8% less bias in estimates of Ktrans. Thus, the extended graphical model may allow kinetic modeling of DCE‐MRI results with shortened data acquisition periods, without sacrificing accuracy in estimates of Ktrans and vp. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.
Spatially dependent filtering for removing phase distortions at the cortical surface
Authors: Ng Amanda , Johnston Leigh , Chen Zhaolin , Cho Zang‐Hee , Zhang Jingxin , Egan Gary
Published: March 2011

Recent advances in high field magnetic resonance technology have increased the interest in the phase of the complex data. Processed phase images are derived from the phase signal by removing the bias field and phase wraps from the initial data. However, the usefulness of this data has been hindered by artifacts at the brain/non‐brain surface, particularly in cortical regions. A method is proposed that efficiently removes surface artifacts by performing Gaussian filtering with spatially varying parameters of unwrapped or complex filtered phase images. The proposed method is shown to produce improved images, revealing underlying structure and detail that are otherwise obscured by surface artifacts in images produced by traditional phase processing methods. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.
Multipathway sequences for MR thermometry
Authors: Madore Bruno , Panych Lawrence P. , Mei Chang‐Sheng , Yuan Jing , Chu Renxin
Published: March 2011

MR‐based thermometry is a valuable adjunct to thermal ablation therapies as it helps to determine when lethal doses are reached at the target and whether surrounding tissues are safe from damage. When the targeted lesion is mobile, MR data can further be used for motion‐tracking purposes. The present work introduces pulse sequence modifications that enable significant improvements in terms of both temperature‐to‐noise‐ratio properties and target‐tracking abilities. Instead of sampling a single magnetization pathway as in typical MR thermometry sequences, the pulse‐sequence design introduced here involves sampling at least one additional pathway. Image reconstruction changes associated with the proposed sampling scheme are also described. The method was implemented on two commonly used MR thermometry sequences: the gradient‐echo and the interleaved echo‐planar imaging sequences. Data from the extra pathway enabled temperature‐to‐noise‐ratio improvements by up to 35%, without increasing scan time. Potentially of greater significance is that the sampled pathways featured very different contrast for blood vessels, facilitating their detection and use as internal landmarks for tracking purposes. Through improved temperature‐to‐noise‐ratio and lesion‐tracking abilities, the proposed pulse‐sequence design may facilitate the use of MR‐monitored thermal ablations as an effective treatment option even in mobile organs such as the liver and kidneys. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.
Increasing spoiling efficiency in RF‐spoiled gradient echo sequences by averaging of RF phase‐cycle‐adaptedk‐spaces
Authors: Leupold Jochen , Hennig Jürgen
Published: March 2011

A method is presented that improves the effectiveness of RF‐spoiling whenever an image consists of the averaging of several identical single acquisitions. Using this method, it becomes possible to reduce the necessary moment of the spoiler gradient by a factor equal to the number of averages. The idea is to perform the collection ofk‐space lines such that the averaging takes over a part of the spoiling process. The number of sequence cycles played out between two acquisitions of a certaink‐space line is adjusted based on both the number of total averages of this line and the phase‐cycling pattern of the RF‐pulse train of a RF‐spoiled gradient echo sequence. In this way, ghost artifacts visible in the single images add to zero in the averaged image while the depiction of the object experiences normal averaging with enhanced signal‐to‐noise ratio. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.
Structure and function of the skeletal muscle extracellular matrix
Authors: Gillies Allison R. , Lieber Richard L.
Published: March 2011

The skeletal muscle extracellular matrix (ECM) plays an important role in muscle fiber force transmission, maintenance, and repair. In both injured and diseased states, ECM adapts dramatically, a property that has clinical manifestations and alters muscle function. Here we review the structure, composition, and mechanical properties of skeletal muscle ECM; describe the cells that contribute to the maintenance of the ECM; and, finally, overview changes that occur with pathology. New scanning electron micrographs of ECM structure are also presented with hypotheses about ECM structure–function relationships. Detailed structure–function relationships of the ECM have yet to be defined and, as a result, we propose areas for future study. Muscle Nerve 44: 318–331, 2011
Looking for differences in copy number between blood and brain in sporadic amyotrophic lateral sclerosis
Authors: Pamphlett Roger , Morahan Julia M. , Luquin Natasha , Yu Bing
Published: March 2011

Introduction: Most analyses of blood DNA in sporadic neuromuscular disorders have been inconclusive. This may be because some genetic variants occur only in brain tissue. We therefore looked for copy number variants (CNVs) in both blood and brain in patients with sporadic amyotrophic lateral sclerosis (SALS). Methods:
Genome‐wide CNVs were compared in blood and brain from 32 SALS patients and from 26 normal (control) brains, using Affymetrix 6.0 arrays. Results: There were 410 CNVs present in brain but not blood (somatic CNVs) in 94% of the patients (median 8 CNVs per patient). Twenty‐four of the somatic CNVs were rare, were not found in control brains, and overlapped with genes. Conclusions: Brain‐specific CNVs may be common and appear to be present in a proportion of patients with SALS. The more detailed copy number analysis that is becoming available with massively parallel sequencing may uncover brain‐specific CNVs that underlie some cases of SALS. Muscle Nerve, 2011
Transmit gain calibration for nonproton MR using the Bloch–Siegert shift
Authors: Schulte Rolf F. , Sacolick Laura , Deppe Martin H. , Janich Martin A. , Schwaiger Markus , Wild Jim M. , Wiesinger Florian
Published: March 2011

Transmit gain (B) calibration is necessary for the adjustment of radiofrequency (RF) power levels to the desired flip angles. In proton MRI, this is generally an automated process before the actual scan without any user interaction. For other nuclei, it is usually time consuming and difficult, especially in the case of hyperpolarised MR. In the current work, transmit gain calibration was implemented on the basis of the Bloch–Siegert phase shift. From the same data, the centre frequency, line broadening and SNR could also be determined. The T1 and B0 insensitivity, and the wide range of B over which this technique is effective, make it well suited for nonproton applications. Examples are shown for hyperpolarised 13C and 3He applications. Copyright © 2011 John Wiley & Sons, Ltd.
MR evaluation of response to targeted treatment in cancer cells
Authors: Podo Franca , Canevari Silvana , Canese Rossella , Pisanu Maria Elena , Ricci Alessandro , Iorio Egidio
Published: March 2011

The development of molecular technologies, together with progressive sophistication of molecular imaging methods, has allowed the further elucidation of the multiple mutations and dysregulatory effects of pathways leading to oncogenesis. Acting against these pathways by specifically targeted agents represents a major challenge for current research efforts in oncology. As conventional anatomically based pharmacological endpoints may be inadequate to monitor the tumor response to these targeted treatments, the identification and use of more appropriate, noninvasive pharmacodynamic biomarkers appear to be crucial to optimize the design, dosage and schedule of these novel therapeutic approaches. An aberrant choline phospholipid metabolism and enhanced flux of glucose derivatives through glycolysis, which sustain the redirection of mitochondrial ATP to glucose phosphorylation, are two major hallmarks of cancer cells. This review focuses on the changes detected in these pathways by MRS in response to targeted treatments. The progress and limitations of our present understanding of the mechanisms underlying MRS‐detected phosphocholine accumulation in cancer cells are discussed in the light of gene and protein expression and the activation of different enzymes involved in phosphatidylcholine biosynthesis and catabolism. Examples of alterations induced in the MRS choline profile of cells exposed to different agents or to tumor environmental factors are presented. Current studies aimed at the identification in cancer cells of MRS‐detected pharmacodynamic markers of therapies targeted against specific conditional or constitutive cell receptor stimulation are then reviewed. Finally, the perspectives of present efforts addressed to identify enzymes of the phosphatidylcholine cycle as possible novel targets for anticancer therapy are summarized. Copyright © 2011 John Wiley & Sons, Ltd.
MR elastography monitoring of tissue‐engineered constructs
Authors: Othman Shadi F. , Curtis Evan T. , Plautz Sarah A. , Pannier Angela K. , Butler Stephanie D. , Xu Huihui
Published: March 2011

The objective of tissue engineering (TE) is to create functional replacements for various tissues; the mechanical properties of these engineered constructs are critical to their function. Several techniques have been developed for the measurement of the mechanical properties of tissues and organs; however, current methods are destructive. The field of TE will benefit immensely if biomechanical models developed by these techniques could be combined with existing imaging modalities to enable noninvasive, dynamic assessment of mechanical properties during tissue growth. Specifically, MR elastography (MRE), which is based on the synchronization of a mechanical actuator with a phase contrast imaging pulse sequence, has the capacity to measure tissue strain generated by sonic cyclic displacement. The captured displacement is presented in shear wave images from which the complex shear moduli can be extracted or simplified by a direct measure, termed the shear stiffness. MRE has been extended to the microscopic scale, combining clinical MRE with high‐field magnets, stronger magnetic field gradients and smaller, more sensitive, radiofrequency coils, enabling the interrogation of smaller samples, such as tissue‐engineered constructs. The following topics are presented in this article: (i) current mechanical measurement techniques and their limitations in TE; (ii) a description of the MRE system, MRE theory and how it can be applied for the measurement of mechanical properties of tissue‐engineered constructs; (iii) a summary of in vitro MRE work for the monitoring of osteogenic and adipogenic tissues originating from human adult mesenchymal stem cells (MSCs); (iv) preliminary in vivo studies of MRE of tissues originating from mouse MSCs implanted subcutaneously in immunodeficient mice with an emphasis on in vivo MRE challenges; (v) future directions to resolve current issues with in vivo MRE in the context of how to improve the future role of MRE in TE. Copyright © 2011 John Wiley & Sons, Ltd.
A novel background field removal method for MRI using projection onto dipole fields (PDF)
Authors: Liu Tian , Khalidov Ildar , de Rochefort Ludovic , Spincemaille Pascal , Liu Jing , Tsiouris A. John , Wang Yi
Published: March 2011

For optimal image quality in susceptibility‐weighted imaging and accurate quantification of susceptibility, it is necessary to isolate the local field generated by local magnetic sources (such as iron) from the background field that arises from imperfect shimming and variations in magnetic susceptibility of surrounding tissues (including air). Previous background removal techniques have limited effectiveness depending on the accuracy of model assumptions or information input. In this article, we report an observation that the magnetic field for a dipole outside a given region of interest (ROI) is approximately orthogonal to the magnetic field of a dipole inside the ROI. Accordingly, we propose a nonparametric background field removal technique based on projection onto dipole fields (PDF). In this PDF technique, the background field inside an ROI is decomposed into a field originating from dipoles outside the ROI using the projection theorem in Hilbert space. This novel PDF background removal technique was validated on a numerical simulation and a phantom experiment and was applied in human brain imaging, demonstrating substantial improvement in background field removal compared with the commonly used high‐pass filtering method. Copyright © 2011 John Wiley & Sons, Ltd.
Efficient γ‐aminobutyric acid editing at 3T without macromolecule contamination: MEGA‐SPECIAL
Authors: Near Jamie , Simpson Robin , Cowen Philip , Jezzard Peter
Published: March 2011

One of the most commonly used methods for in vivo MRS detection of γ‐aminobutyric acid (GABA) is the MEGA‐point‐resolved spectroscopy (MEGA‐PRESS) technique. However, accurate quantification of GABA using MEGA‐PRESS is complicated by spectral co‐editing of macromolecular resonances. In this article, a new pulse sequence is presented which enables GABA editing at 3T with the removal of macromolecule contamination. This sequence combines the conventional MEGA editing scheme with the SPECIAL localisation technique, and is therefore named MEGA‐SPECIAL. Simulations and phantom experiments indicate that this new approach provides improved GABA editing efficiency relative to MEGA‐PRESS, and in vivo results demonstrate effective removal of macromolecule contamination. In a study of the occipital lobe of five healthy volunteers, the macromolecule‐corrected GABA/creatine ratio was found to be 0.093 ± 0.007 (mean ± standard deviation), whereas prior to macromolecule correction, the ratio was found to be 0.173 ± 0.013. Copyright © 2011 John Wiley & Sons, Ltd.
Diffusion‐weighted MRI in early chemotherapy response evaluation of patients with diffuse large B‐cell lymphoma – a pilot study: comparison with 2‐deoxy‐2‐fluoro‐ D‐glucose‐positron emission tomography/computed tomography
Authors: Wu Xingchen , Kellokumpu‐Lehtinen Pirkko‐Liisa , Pertovaara Hannu , Korkola Pasi , Soimakallio Seppo , Eskola Hannu , Dastidar Prasun
Published: March 2011

To determine the feasibility of diffusion‐weighted MRI (DWI) in the evaluation of the early chemotherapeutic response in patients with aggressive non‐Hodgkin's lymphoma (NHL), eight patients with histologically proven diffuse large B‐cell lymphoma were imaged by MRI, including DWI, and positron emission tomography/computed tomography (PET/CT) before treatment (E1), and after 1 week (E2) and two cycles (E3) of chemotherapy. In all patients, whole‐body screening using T1‐ and T2‐weighted images in the coronal plane was performed. To quantitatively evaluate the chemotherapeutic response, axial images including DWI were acquired. Apparent diffusion coefficient (ADC) maps were reconstructed, and the ADC value of the tumor was measured. In addition, the tumor volume was estimated on axial T2‐weighted images. The maximum standardized uptake value (SUVmax) and active tumor volume were measured on fused PET/CT images. Lymphomas showed high signal intensity on DW images and low signal intensity on ADC maps, except for necrotic foci. The mean pre‐therapy ADC was 0.71 × 10−3 mm2/s; it increased by 77% at E2 (p < 0.05) and 24% more at E3 (insignificant); the total increase was 106% (p < 0.05). The mean tumor volume by MRI was 276 mL at baseline; it decreased by 58% at E2 (p < 0.05) and 65% more at E3 (p < 0.05), giving a total decrease of 84% (p < 0.05). All the imaged pre‐therapy tumors were strongly positive on PET/CT, with a mean SUVmax of 20. The SUVmax decreased by 60% at E2 (p < 0.05) and 59% more at E3 (p < 0.05), giving a total decrease of 83% (p < 0.05). The active tumor burden decreased by 66% at E2 (p < 0.05). At baseline, both central and peripheral tumor ADC values correlated inversely with SUVmax (p < 0.05), and also correlated inversely with active tumor burden on PET/CT and with tumor volume on MRI at E2 (p < 0.05). In conclusion, the results of DWI in combination with whole‐body MRI were comparable with those of integrated PET/CT. Copyright © 2011 John Wiley & Sons, Ltd.
Detection accuracy of network anomalies using sampled flow statistics
Authors: Kawahara Ryoichi , Ishibashi Keisuke , Mori Tatsuya , Kamiyama Noriaki , Harada Shigeaki , Hasegawa Haruhisa , Asano Shoichiro
Published: March 2011

We investigated the detection accuracy of network anomalies when using flow statistics obtained through packet sampling. Through a case study based on measurement data, we showed that network anomalies generating a large number of small flows, such as network scans or SYN flooding, become difficult to detect during packet sampling. We then developed an analytical model that enables us to quantitatively evaluate the effect of packet sampling and traffic conditions, such as anomalous traffic volume, on detection accuracy. We also investigated how the detection accuracy worsens when the packet sampling rate decreases. In addition, we show that, even with a low sampling rate, spatially partitioning monitored traffic into groups makes it possible to increase detection accuracy. We also developed a method of determining an appropriate number of partitioned groups, and we show its effectiveness. Copyright © 2011 John Wiley & Sons, Ltd.
A Bessel collocation method for numerical solution of generalized pantograph equations
Authors: Yüzbaşi Şuayip , Şahin Niyazi , Sezer Mehmet
Published: March 2011

This article is concerned with a generalization of a functional differential equation known as the pantograph equation which contains a linear functional argument. In this article, we introduce a collocation method based on the Bessel polynomials for the approximate solution of the pantograph equations. The method is illustrated by studying the initial value problems. The results obtained are compared by the known results. © 2011 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2011