bluuebunny/crossref_metadata_2025_split huggingface dataset:
Environmentally Friendly Films Made With a New Family of Linear Ethylene Polymers
Authors: Halle Richard W. 
Published: March 2007

The public's ever-increasing environmental consciousness is driv ing the plastics packaging industry to constantly consider the complete life cy cle of their products. One avenue by which packaging film producers are responding to the "green" movement is by manufacturing polyolefin-based films containing Post-Consumer Recycled (PCR) polyolefins. These types of films are commercial in a wide variety of end uses, many of which have been tradition ally serviced by films made from high pressure process-low density polyethyl ene (HRLDPE). One obvious technical approach toward improving on this effort is to produce a film having as high a recycle content as possible but with a strength and toughness similar to that of the original HP-LDPE films. Any polymer which could effectively incorporate very high (50% +) levels of PCR into these type films would be of significant interest to the industry. Several new linear ethylene polymers have been used to increase the recycle content of these type films to very high levels while maintaining good film toughness properties. A series of blown films produced during an early screen ing study demonstrated the good physical properties and acceptable processing characteristics of these high PCR content blends containing these unique linear ethylene polymers.
How cost-effective is screening for abdominal aortic aneurysms?
Authors: Kim L G , Thompson S G , Briggs A H , Buxton M J , Campbell H E 
Published: March 2007

Objective: To provide reliable estimates of the long-term cost-effectiveness of abdominal aortic aneurysm screening in men. Methods: A Markov health economic decision model for screening is described and extrapolated to 30 years. The strategy modelled involves a one-off scan at age 65 years, with annual and three-monthly follow-up scans for small and medium aneurysms, respectively. Referral for elective surgery occurs at an aortic diameter of 5.5 cm. Model parameters are estimated from patient-level data from the UK Multi-centre Aneurysm Screening Study. Model structure is validated on this trial's data, and input parameter uncertainty is addressed by probabilistic sensitivity analysis. Costs and life-years gained are obtained for both screening and no systematic screening strategies. Results: Cost-effectiveness improves dramatically when considered over longer timescales. Taking a 30-year perspective, screening for abdominal aortic aneurysms in men is highly cost-effective at £2320 per life-year gained (95% uncertainty interval: £1600 to £4240). Adjusting life-years for the age-specific health-related quality of life experienced in this population gave a figure of £2970 (95% uncertainty interval: £2030 to £5430) per quality-adjusted life-year gained. The additional cost of screening the UK male population is estimated to be £19 m per year. Conclusions: The long-term cost-effectiveness of screening for abdominal aortic aneurysms in men is highly attractive and this evidence provides further support for a national screening programme in the UK.
Evidence for the dissociation of the hepatobiliary MRI contrast agent Mn‐DPDP
Authors: Gallez Bernard , Bacic Goran , Swartz Harold M. 
Published: March 2007

AbstractThese experiments assessed and quantitated the release of free manganese Mn++ from the hepatobiliary contrast agent Mn‐DPDP (manganese dipyridoxal diphosphate), using several magnetic resonance techniques (EPR spectroscopy, 31P‐NMR spectroscopy, and relaxometry) to differentiate between free Mn++ and Mn++ in complexes in various preparations. The presence of calcium and magnesium in physiological concentrations in aqueous solutions induced the release of Mn++ from the complex, as did incubation of the complex in liver homogenates. After intravenous injection of 15 μmol/kg of Mn‐DPDP, both EPR and 31P‐NMR spectroscopy demonstrated that Mn‐DPDP is partly dissociated (approximately 25%) in the liver. By comparing in vitro and ex vivo data from the liver, we concluded that the dissociation of Mn‐DPDP occurs primarily in the liver, whereas a minor portion of the dissociated Mn found in the liver comes from dissociation of the complex in the blood. Most of the dissociated Mn in liver becomes bound to macromolecules and is responsible for the enhancement of relaxivity observed with this agent.
Perfusion changes in human skeletal muscle during reactive hyperemia measured by echo‐planar imaging
Authors: Toussaint Jean‐François , Kwong Kenneth K. , M′Kparu Fidelis , Weisskoff Robert M. , Laraia Paul J. , Kantor Howard L. 
Published: March 2007

AbstractMuscle performance is markedly influenced by tissue perfu‐sion. Techniques that allow quantification of microvascular flow are limited by the use of ionizing radiation. In this investigation, we apply an NMR model previously developed by Detre ef al. to the measurement of human muscle perfusion during reactive hyperemia. We compare our results with conventional plethysmography adapted to NMR. Using echo‐planar imaging, T1 and T2 were measured in 14 subjects during rest, ischemia, and reactive hyperemia. Mean leg muscle T1 in healthy volunteers is 850 ms at rest and 834 ms at reperfusion, leading to a calculated reactive hyperemia flow increase (T1 flow) of 103 ± 40 ml/100 ml/min. T1 flows correlate well with NMR‐plethysmography values. Changes in T2, which are sensitive to both deoxyhemoglobin content and vessel diameter variations, are also correlated with perfusion measurements. T1 changes allow quantification of regional perfusion in human muscle during reactive hyperemia.
Perfusion imaging with compensation for asymmetric magnetization transfer effects
Authors: Pekar James , Jezzard Peter , Roberts David A. , Leigh John S. , Frank Joseph A. , McLaughlin Alan C. 
Published: March 2007

AbstractThe effects of off‐resonance radio‐frequency irradiation on the intensity of the MR signal from water protons in the cat brain are asymmetric around the chemical shift of the water signal. This asymmetry, which could arise from a shift in the magnetization transfer spectrum ˜1.5 ppm upfield from the solvent water signal, must be taken into account to compensate for magnetization transfer effects inherent in arterial spin tagging approaches that use a single radio‐frequency coil. Two approaches that either correct for, or circumvent, the apparent upfield shift of the magnetization transfer spectrum are presented, and a perfusion image of the cat brain, using flow‐induced adiabatic inversion of arterial water protons, is presented. Other problems in obtaining quantitative cerebral blood flow values using the arterial spin tagging approach are discussed.
Reperfused ischemia of the rat intestine: Detection by MR imaging with polylysine‐Gd‐DTPA enhancement
Authors: Mottet Isabelle , van Beers Bernard E. , Delos Monique , Goudemant Jean‐François , Jamart Jacques , Demeure Roger , Pringot Jacques 
Published: March 2007

AbstractTo detect reperfused ischemia of the rat intestine, T2‐weighted spin‐echo images were acquired, followed by T1‐weighted images before and after administration of polylysine‐Gd‐DTPA or Gd‐DTPA. Before administration of the contrast agent, the reperfused intestine was hyperintense on T2‐weighted images, and to a lesser extent on T1‐weighted images. After administration of polylysine‐Gd‐DTPA, the reperfused intestine enhanced more than the normal one, giving a significantly better contrast‐to‐noise (CNR) ratio than on unenhanced images. Gd‐DTPA induced the same enhancement of the reperfused and the normal intestine and the CNR was lower than on unenhanced T2‐weighted images. Reperfused intestinal ischemia could thus be better detected on polylysine‐Gd‐DTPA‐enhanced MR images than on unenhanced images or on Gd‐DTPA‐ enhanced images.
Noninvasive measurement of protein concentration
Authors: Jiao Xiaoqi , Bryant Robert G. 
Published: March 2007

AbstractAt selected magnetic field strengths, protein and water proton spin‐lattice relaxation rates are sensitive to the concentration of rotationally immobilized peptide nitrogen because of field dependent heteronuclear cross relaxation coupling between protein proton and nitrogen‐14 spins that is carried to the water by proton homonuclear cross‐relaxation. Measurement of the water proton spin‐lattice relaxation time, or a signal amplitude proportional to it, may provide a noninvasive measure of peptide bond concentration, which provides a direct measure of immobilized protein content in most tissues. The approach using protein gels in two magnetic field strengths is demonstrated. At 66.7 mT, the proton Zeeman energy matches one of the peptide nitrogen transitions dominated by the unaveraged nuclear electric quadrupole interaction; cross‐relaxation between the protons and nitrogen‐14 is efficient At 77.5 mT, the proton Zeeman energy is not matched with the nitrogen energy and proton‐nitrogen cross‐relaxation is not efficient. It is shown that the difference in the water proton spin‐lattice relaxation rates on and off the energy level match condition is a linear function of the rotation‐ally immobilized protein concentration.
Effects of osmotically driven cell volume changes on diffusion‐weighted imaging of the rat optic nerve
Authors: Anderson Adam W. , Zhong Jianhui , Petroff Ognen A. C. , Szafer Aaron , Ransom Bruce R. , Prichard James W. , Gore John C. 
Published: March 2007

AbstractThe apparent diffusion coefficient (ADC) of the rat optic nerve was measuredIn vitro, using magnetic resonance imaging, to determine the effects of changes in cellular volume fraction on the diffusion of tissue water. Nerve ADC was determined under conditions of cell membrane depolarization and (i) increased intracellular volume, (ii) decreased intracellular volume, and (iii) negligible volume change. Depolarization alone had little affect on ADC, whereas volume changes produced strong, reversible effects. Increased cell volume decreased ADC andvice versa. These results are consistent with the view that changes in the extracellular space are the major source of ADC changes in brain tissue.
Comparison of ultrafast dipyridamole magnetic resonance imaging with dipyridamole sestamibi SPECT for detection of perfusion abnormalities in patients with one‐vessel coronary artery disease: Assessment by quantitative model fitting
Authors: Matheijssen Niels A. A. , Louwerenburg Hans W. , van Rugge F. Paul , Arens Ruud Pj. H. , Kauer Ben , de Roos Albert , van der Wall Ernst E. 
Published: March 2007

AbstractThe value of ultrafast MRI for detection of myocardial perfusion abnormalities in patients with coronary artery disease (CAD) was assessed in 10 patients with stable angina pectoris and angiographically proven one‐vessel CAD using double‐level short‐axis ultrafast MRI with bolus injection of gadolinium‐DTPA and tomographic technetium‐99m SestaMIBI imaging (SPECT) during dipyridamole‐induced coronary hy‐peremia. Abnormally perfused regions were assessed with SPECT and MRI in all (100%) patients. Agreement in localization between arteriography and SPECT was 80%; between arteriography and MR, 70%; and between SPECT and MR, 90%. The signal intensity increase after the bolus injection of gadolinium‐DTPA using a linear fit, and the slope of gado‐linium‐DTPA wash‐in using double exponential model fitting were significantly different between abnormally and normally perfused regions. These preliminary results demonstrate the potential of dipyridamole ultrafast MR to monitor stress‐induced flow maldistribution in patients with single vessel CAD.
Calibration of the radio frequency field for magnetic resonance imaging
Authors: Foxall David L. , Hoppel Bernice E. , Hariharan Hari 
Published: March 2007

AbstractWe have developed and validated the performance of a novel slice selective pulse sequence that allows direct calibration of the RF field using a simple rectangular pulse. The new sequence offers a number of substantial advantages. It operates at steady state and has an accurate calibration response at short repetition times. The slice selection train is insensitive to RF field strength changes caused by patient loading. The issue of patient motion has been addressed in our data collection and analysis routines. The applicability of the method to human scanning has been demonstrated in the automated RF power calibration routine of a commercial imaging system.
A new ytterbium chelate as contrast agent in chemical shift imaging and temperature sensitive probe for MR spectroscopy
Authors: Aime Silvio , Botta Mauro , Fasano Mauro , Terreno Enzo , Kinchesh Paul , Calabi Luisella , Paleari Lino 
Published: March 2007

AbstractA paramagnetic Yb(lll) complex that is the prototype of a novel class of probes for MRI and MRS has been developed. The complex displays highly shifted 1H resonances that are characterized by short relaxation times and, as such, may prove to be a valuable alternative in applications that currently require fluorine‐containing probes. Selective excitation of the para‐magnetically shifted resonances allows the spatial distribution of the complex to be mapped. This communication reports the images that were obtained by selectively exciting the most intense methyl group (−14.2 ppm at 27°C) for complex concentrations ranging from 0.003−0.1 M. Spectroscopically, the complex may be used as a temperature probe since the proton chemical shifts exhibit a strong temperature dependence. In human serum the chemical shift difference of a selected pair of proton resonances was observed to follow a gradient of −0.42 ± 0.01 ppm/°C. Furthermore, since the chemical shift of the methyl resonance displays a temperature coefficient of −0.04 ± 0.01 ppm/°C, it should be possible to use the image phase for thermal mapping.
Human cardiac high‐energy phosphate metabolite concentrations by 1D‐resolved NMR spectroscopy
Authors: Bottomley Paul A. , Atalar Ergin , Weiss Robert G. 
Published: March 2007

AbstractWe have developed a method that can measure high‐energy phosphate metabolite concentrations in humans with 1D resolved surface‐coil NMR spectroscopy. The metabolites are measured by phosphorus (31P) NMR spectroscopy, and the tissue water proton (1H) resonance from the same volume serves as an internal concentration reference. The method requires only the additional acquisition of a 1H data set, and a simple calibration, performed separately, to determine the ratio of the signal per proton to the signal per phosphorus nucleus. The quantification method is particularly useful for human cardiac spectroscopy, where it eliminates image‐based tissue volumetry and the corrections for signal sensitivity and phase nonuniformity necessary in prior approaches. Corrections are introduced to account for blood and fat contributions to the spectra. The method was validated on phantoms of phosphate of varying concentrations and on the human calf muscle. In calf, the adenosine triphosphate (ATP) and phosphocreatine (PCr) concentrations were 5.6 ± 1.6 (mean ± SD) and 26 ± 4 mmol/kg wet wt, respectively. In normal heart, [ATP] was 5.8 ± 1.6 and [PCr] was 10 ± 2 mmol/kg wet wt. These values are in excellent agreement with prior NMR studies and biopsy data. The protocol is easily accommodated within existing 1D cardiac patient protocols, and the same approach is advantageous for eliminating tissue volumetry and sensitivity corrections when measuring concentrations by 2D and 3D resolved spectroscopy.
Single‐shot diffusion MRI of human brain on a conventional clinical instrument
Authors: Liu Guoying , Van Gelderen Peter , Duyn Jeff , Moonen Chrit T. W. 
Published: March 2007

AbstractA single‐shot diffusion MRI technique on a standard clinical 1.5T scanner is presented. The method incorporates the following elements: (a) an inversion RF pulse followed by a delay of 1.3 s to null cerebral spinal fluid (CSF) signal, (b) a stimulated echo sequence (TE=56 ms, TM=100 ms) to obtain strong diffusion weighting, (c) a single‐shot gradient‐ and spin‐echo (GRASE) sequence for imaging with a modified k‐space trajectory and Carr‐Purcell Meiboom‐Gill (CPMG)‐phase cycle. The trace of the diffusion coefficient obtained with this approach is in good agreement with values reported for animal brain, and for recent human studies. It is demonstrated that single‐shot diffusion imaging of human brain is feasible on an unmodified standard instrument without high‐gradient slew rate or extreme field homogeneity.
Metabolite 1H relaxation in normal and hyponatremic brain
Authors: Rooney William D. , Ebisu Toshihiko , Mancuso Anthony , Graham Steven , Weiner Michael W. , Maudsley Andrew A. 
Published: March 2007

AbstractProton spin relaxation rate constants in normal and hyponatremic rat brain were measured to determine the sensitivity of metabolite relaxation properties to cytotoxic edema and to quantify metabolite concentration in normal and edematous brain. Relaxation rate constants for protons of water and spectral regions with dominant contributions from methyl protons of cholines (Cho), creatines (Cr), N‐acetylaspartate (NA), and lactate (Lac), and for methylene protons of glutamate (Glu) were measured at 7 T. Changes in metabolite relaxation properties associated with cytotoxic edema were a decrease in the Cr longitudinal rate constant, from 0.63 ± 0.02 s−1 (mean ± SE) in controls to 0.50 ± 0.03 s−1 in edematous brain, and an increase in the transverse rate constant of NA from 5.3 ± 0.2 s−1 in controls to 6.6 ± 0.3 s−1 in edematous brain. Four hours after induction of hyponatremia, there was a 14% reduction in summed metabolite concentrations of Cho, Cr, and NA, and a 200% increase in Lac signal intensity. It is concluded that changes in both metabolite spin relaxation and detectable spin concentration accompany the cerebral pathology of cytotoxic edema complicated with secondary ischemia.
NMR studies on water and polymer diffusion in dextran gels. Influence of potassium ions on microstructure formation and gelation mechanism
Authors: Watanabe Tokuko , Ohtsuka Akihiro , Murase Norio , Barth Peter , Gersonde Klaus 
Published: March 2007

AbstractAt room temperature aqueous solutions of dextrans with concentrations >25% (w/w) exhibit a sol‐gel transition in the presence of >1.0 M potassium chloride. In dextrans the gelation was unexpected due to missing anionic groups that usually provide the binding sites for cations. The quantitative investigation of the gel formation is based on changes of the diffusibility of water and dextran chains. The apparent diffusion coefficients of bulk water (in the order of 10−6 cm2/s) and of water trapped in the junction zones as well as of polymer chains (in the order of 10−7 to 10−8 cm2/s) are determined by employing pulsed field gradient stimulated echo (PFGSTE) NMR. The restricted diffusion of bulk water in viscous sols and in soft and rigid gels has been quantitatively analyzed providing data for interbarrier distances (pore size), permeabilities of the diffusion barriers (density of junction zones) and interbarrier diffusion coefficients of water. Based on already published x‐ray structure data and in accordance with the diffusion data presented in this paper “potassium‐bonding” is assumed to be the most important interaction for the formation of a microstructure and for the stabilization of crosslinks. The ionic radius of the potassium ion perfectly fits to the cage established by six oxygen atoms of glucose units of three polymer chains. Other cations, such as Li+, Na+, Rb+ and Cs+, according to their nonfitting ionic radii, do not provoke dextran gelation under these conditions. The mechanism of the transitions from sol to soft gel and further to rigid gel is discussed on the basis of restricted diffusion and x‐ray structure data.
Frequency response of multi‐phase segmented k‐space phase‐contrast
Authors: Polzin Jason A. , Frayne Richard , Grist Thomas M. , Mistretta Charles A. 
Published: March 2007

AbstractA theoretical analysis of the temporal frequency response of multi‐phase segmented k‐space phase‐contrast was developed. This includes the effects of both segment duration and the number of cardiac phases that are reconstructed. An increase in the number of views per segment and the corresponding increase in segment duration results in an increased smoothing or low‐pass filtering of the time‐resolved flow waveform. Reconstruction of all intermediate cardiac phases makes the Nyquist sampling frequency independent of the number of views per segment. This analysis was verified experimentally using a multi‐phase phase‐contrast segmented k‐space MR pulse sequence. This sequence reconstructs all intermediate cardiac phases and uses fractional segments at the end of the cardiac cycle if an entire segment does not fit. The use of fractional segments increases the portion of the cardiac cycle over which data are acquired.
Detecting cortical activities from fMRI time‐course data using the music algorithm with forward and backward covariance averaging
Authors: Sekihara Kensuke , Koizumi Hideaki 
Published: March 2007

AbstractA method is proposed for processing time‐course fMRI data taken wKh successlve single‐shot echo‐planar imaging. The proposed method uses a two‐dimensional version of the multiple signal classification (MUSIC) algorithm and the technique called covariance averaging, both of which were developed in the field of sensor‐array processing. The proposed method consists of four steps: calculate the averaged data covariance matrix, determine the number of activities using this covariance matrix, estimate the locations of the activities, and estimate their time evolution curves. Computer simulation resutts showed that a nearly fourfold improvement in the spatial resolution can be attained due to the method's super‐resolution capability.
Pencil excitation with interleaved fourier velocity encoding: NMR measurement of aortic distensibility
Authors: Hardy Christopher J. , Bolster Bradley D. , McVeigh Elliot R. , Iben Icko E. T. , Zerhouni Elias A. 
Published: March 2007

AbstractA technique is presented for rapidly and noninvasively determining aortic distensibiltty, by NMR measurement of pulse‐wave velocrty in the aorta. A cylinder of magnetization is excited along the aorta, wtth Fourier‐veloctty encoding and readout gradients applied along the cylinder axis. Cardiac gating and data interleaving improve the effective time resolution to as high as 3 ms. Wave velocities are determined from the position of the f oot of the flow wave in the velocity profiles. Evidence of helical flow distal to the aortic arch can be seen in normal subjects, while disturbed flow patterns are visible in patients with aneurysms and dissections.
Regional myocardial oxygen tension: 19F MRI of sequestered perfluorocarbon
Authors: Shukla Himu P. , Mason Ralph P. , Bansal Navin , Antich Peter P. 
Published: March 2007

AbstractA novel noninvasive method of measuring local myocardial oxygen tension (pO2) In the perfused rat heart using 19F MRI is demonstrated. Tissue pO2 was determined on the basis of the 19F spin‐lattice relaxation rate (R1) of perflubron (perfluorooctyl bromide) sequestered in the heart after IV infusion of an emulsion. Spectroscopic measurement of R1 was previously used to measure a global weighted average of oxygen status. 19F MRI now provides 3D spatial resolution indicating local cardiac pO2 under normally perfused, globally ischemic, and regionally ischemic conditions.