bluuebunny/crossref_metadata_2025_split huggingface dataset:
Automatic segmentation of the brain and intracranial cerebrospinal fluid in T1‐weighted volume MRI scans of the head, and its application to serial cerebral and intracranial volumetry
Authors: Lemieux Louis , Hammers Alexander , Mackinnon Toby , Liu Rebecca S.N. 
Published: April 2003

AbstractA new fully automatic algorithm for the segmentation of the brain and total intracranial cerebrospinal fluid (CSF) from T1‐weighted volume MRI scans of the head, called Exbrain v.2, is described. The algorithm was developed in the context of serial intracranial volumetry. A brain mask obtained using a previous version of the algorithm forms the basis of the CSF segmentation. Improved brain segmentation is then obtained by iterative tracking of the brain–CSF interface. Gray matter (GM), white matter (WM), and intracranial CSF volumes and probability maps are calculated based on a model of intensity probability distribution (IPD) that includes two partial volume classes: GM‐CSF and GM‐WM. Accuracy was assessed using the Montreal Neurological Institute's (MNI) digital phantom scan. Reproducibility was assessed using scan pairs from 24 controls and 10 patients with epilepsy. Segmentation overlap with the gold standard was 98% for the brain and 95%, 96%, and 97% for the GM, WM, and total intracranial contents, respectively; CSF overlap was 86%. In the controls, the Bland and Altman coefficient of reliability (CR) was 35.2 cm3 for the total brain volume (TBV) and 29.0 cm3 for the intracranial volume (ICV). Scan‐matching reduced CR to 25.2 cm3 and 17.1 cm3 for the TBV and ICV, respectively. For the patients, similar CR values were obtained for the ICV. Magn Reson Med 49:872–884, 2003. © 2003 Wiley‐Liss, Inc.
Arterial spin labeling perfusion fMRI with very low task frequency
Authors: Wang Jiongjiong , Aguirre Geoffrey K. , Kimberg Daniel Y. , Roc Anne C. , Li Lin , Detre John A. 
Published: April 2003

AbstractFunctional magnetic resonance imaging (fMRI) has become the most widely used modality for visualizing regional brain activation in response to sensorimotor or cognitive tasks. While the majority of fMRI studies have used blood oxygenation level‐dependent (BOLD) contrast as a marker for neural activation, baseline drift effects result in poor sensitivity for detecting slow variations in neural activity. By contrast, drift effects are minimized in arterial spin labeling (ASL) perfusion contrast, primarily as a result of successive pairwise subtraction between images acquired with and without labeling. Recent data suggest that ASL contrast shows stable noise characteristics over the entire frequency spectrum, which makes it suitable for studying low‐frequency events in brain function. The present study investigates the relative sensitivities of ASL and BOLD contrast in detecting changes in motor cortex activation over a spectrum of frequencies of experimental design, where the alternating period between the resting state and activation is varied from 30 s up to 24 hr. The results demonstrate that 1) ASL contrast can detect differences in motor cortex activation over periods of minutes, hours, and even days; 2) the functional sensitivity of ASL contrast becomes superior to that of BOLD contrast when the alternating period between the resting state and activation is greater than a few minutes; and 3) task activation measured by ASL tends to have less intersubject variability than BOLD contrast. The improved sensitivity of the ASL contrast for low task frequency and longitudinal studies, along with its superior power in group analysis, is expected to extend the range of experimental designs that can be studied using fMRI. Magn Reson Med 49:796–802, 2003. © 2003 Wiley‐Liss, Inc.
Quantitative proton short‐echo‐time LASER spectroscopy of normal human white matter and hippocampus at 4 Tesla incorporating macromolecule subtraction
Authors: Kassem Mohamed N.E. , Bartha Robert 
Published: April 2003

AbstractAccurate quantification of in vivo short‐echo‐time (TE) 1H spectra must account for contributions from both mobile metabolites and less mobile macromolecules, which can fluctuate in disease. The purpose of this study was to develop an approach for the acquisition and processing of macromolecule information to optimize metabolite quantification accuracy and precision. Human parietal white matter (8‐cm3 voxel) and posterior hippocampus (1.7‐cm3 voxel) metabolite levels were quantified, following manomolecule subtraction, from short‐echo‐time spectra (TE = 46 ms) acquired at 4.0 Tesla with localization by adiabatic selective refocusing (LASER). Nineteen metabolites were fit using a time domain Levenberg‐Marquardt minimization that incorporated prior knowledge of metabolite lineshapes. The macromolecule contribution to the spectrum was reduced by 87% (P < 0.05) when the acquisition of single averages of the full spectrum and macromolecule spectrum were interleaved to reduce subtraction errors due to motion. Subtracting the Hankel Lanczos singular value decomposition (HLSVD) fit of the macromolecule spectrum, which contained no random noise, did not alter quantified metabolite levels but did not increase metabolite quantification precision. Several metabolites had higher concentrations in the posterior hippocampus compared to parietal white matter, which emphasizes the need to carefully control for partial volume contamination in hippocampal spectroscopy studies. Magn Reson Med 49:918–927, 2003. © 2003 Wiley‐Liss, Inc.
Fast U‐FLARE‐based correlation‐peak imaging with complete effective homonuclear decoupling
Authors: Mayer Dirk , Dreher Wolfgang , Leibfritz Dieter 
Published: April 2003

AbstractA new fast correlation‐peak imaging technique is presented that combines 2D correlation spectroscopy with an ultrafast low‐angle rapid acquisition with relaxation enhancement (U‐FLARE) imaging module. Constant time chemical shift (CS) encoding is used in both time dimensions to achieve effective homonuclear decoupling in both frequency dimensions. The intervals between excitation and mixing (tc1) and between mixing and start of the MRI module (tc2) can be optimized to maximize the coherence transfer for a particular metabolite. Experiments were performed with evolution times tc1 and tc2 of 100 ms and 50 ms, respectively, which were determined by simulation of the spectroscopic part of the sequence for the spin systems of myo‐inositol (Ins) and taurine (Tau). The use of a circularly reduced CS‐encoding scheme shortened the minimum total measurement time to 35 min. The sequence was implemented on a 4.7 T imaging system and tested on a spherical phantom filled with a solution of Ins. The in vivo application of this method on healthy rat brain demonstrates its improved spectral resolution, as cross‐peak signals from both Ins and Tau can be separated clearly. Magn Reson Med 49:810–816, 2003. © 2003 Wiley‐Liss, Inc.
Quantitative evaluation of susceptibility and shielding effects of nitinol, platinum, cobalt‐alloy, and stainless steel stents
Authors: Wang Yi , Truong Thuy N. , Yen Cecil , Bilecen Deniz , Watts Richard , Trost David W. , Prince Martin R. 
Published: April 2003

AbstractThe purpose of this study is to quantitatively estimate the shielding and susceptibility effects of commonly used metallic stents on MR signal. Two experiments were performed using a 3D gradient echo sequence with short TE to image a stent phantom: 1) short TR and high flip angle (contrast enhanced MRA parameters), and 2) long TR (TR ≫ T1) and low flip angle. The factor characterizing susceptibility effects was estimated from the signal phase of the first experiment, and then the factor characterizing the shielding effects was derived from the second experiment. Susceptibility induced signal loss was negligible (<1%) for nonstainless‐steel (nitinol, platinum, and cobalt‐alloy) stents and totally destructive (100%) for the stainless steel stent. Signal loss due to RF shielding was 31–62% for nitinol stents, 14–50% for platinum stents, 50–77% for the cobalt‐alloy stents (undetermined for the stainless steel stent), varied with stent orientation, diameter, and wall geometry. In summary, stents made of nitinol, platinum, and cobalt‐alloy have negligible susceptibility effects but stents made of stainless steel may have complete dephasing. All stents have substantial shielding effects, which vary with composition, geometry, and orientation. Large platinum stents may have the smallest artifacts and are the best suited for postinterventional MR imaging. Magn Reson Med 49:972–976, 2003. © 2003 Wiley‐Liss, Inc.
Balanced phase‐contrast steady‐state free precession (PC‐SSFP): A novel technique for velocity encoding by gradient inversion
Authors: Markl M. , Alley M.T. , Pelc N.J. 
Published: April 2003

AbstractA technique for measuring velocity is presented that combines cine phase contrast (PC) MRI and balanced steady‐state free precession (SSFP) imaging, and is thus termed PC‐SSFP. Flow encoding was performed without the introduction of additional velocity encoding gradients in order to keep the repetition time (TR) as short as in typical SSFP imaging sequences. Sensitivity to through‐plane velocities was instead established by inverting (i.e., negating) all gradients along the slice‐select direction. Velocity sensitivity (VENC) could be adjusted by altering the first moments of the slice‐select gradients. Disturbances of the SSFP steady state were avoided by acquiring different flow echoes in consecutively (i.e., sequentially) executed scans, each over several cardiac cycles, using separate steady‐state preparation periods. A comparison of phantom measurements with those from established 2D‐cine‐PC MRI demonstrated excellent correlation between both modalities. In examinations of volunteers, PC‐SSFP exhibited a higher intrinsic signal‐to‐noise ratio (SNR) and consequently low phase noise in measured velocities compared to conventional PC scans. An additional benefit of PC‐SSFP is that it relies less on in‐flow‐dependent signal enhancement, and thus yields more uniform SNRs and better depictions of vessel geometry throughout the whole cardiac cycle in structures with slow and/or pulsatile flow. Magn Reson Med 49:945–952, 2003. © 2003 Wiley‐Liss, Inc.
Increased brain white matter diffusivity in normal adult aging: Relationship to anisotropy and partial voluming
Authors: Pfefferbaum Adolf , Sullivan Edith V. 
Published: April 2003

AbstractDiffusion tensor imaging (DTI) was used to examine 1) age‐related changes in genu, splenium, and centrum semiovale white matter diffusivity in 64 healthy men and women (age 23–85 years); 2) the relationship between diffusivity (trace) and fractional anisotropy (FA) across and within individuals; and 3) the role of macrostructural and microstructural partial voluming effects on the DTI metrics. Regional differences were greater in FA (∼43%) than in trace (∼16%). Depending on the region of interest, trace increased with age (r = 0.24 to 0.58) and FA decreased with age (r = −0.29 to −0.79). FA was inversely correlated with trace, even when controlling for age. Histogram analysis of trace and FA following systematic expansion and dilation of the white matter regions demonstrated greater susceptibility of FA than trace to error arising from macrostructural partial voluming, i.e., erroneous inclusion of primarily nonwhite‐matter voxels. Three‐phase ellipsoid shape analysis revealed that after morphometric erosion the spherical component remained greater in older than younger subjects in the splenium and centrum, suggesting that age‐related reduction in FA arises from intravoxel increased interstitial fluid. Reducing the size of the white matter samples to control for macrostructural partial voluming attenuated but did not negate effects, indicating that observed changes in white matter with aging can reflect real microstructural alterations rather than sampling artifact. Morphological dilation of white matter regions of interest resulting in purposeful inclusion of non‐white matter pixels significantly reduced mean FA, suggesting that reports of FA values below 0.25 in healthy adults may reflect partial voluming rather than actual changes in white matter coherence. Magn Reson Med 49:953–961, 2003. © 2003 Wiley‐Liss, Inc.
Physicochemical characterization of dispersed chicken feather keratin
Authors: Ward Wilfred H. , High Loretta M. , Lundgren Harold P. 
Published: April 2003

AbstractReduced chicken feather keratin forms a soluble complex in neutral aqueous sodium alkylbenzenesulfonate (average: dodecylbenzenesulfonate). The chemical composition, specific refractive increment, partial specific volume, electrophoretic mobility, osmotic pressure, diffusion constants, and ultracentrifugal sedimentation of the complex have been studied. The complex is heterogeneous but similar to egg albumin–sodium alkylbenzenesulfonate mixtures previously studied in general properties, including fiber‐forming properties, the average molecular weight of the dispersed protein units, and the relative symmetry of the dispersed units in dilute solution.
Characterization of cellulose derivatives by solution properties: Plasticizers as solvents
Authors: Spurlin H. M. , Martin A. F. , Tennent H. G. 
Published: April 2003

AbstractThe dimensional stability of molded thermoplastic articles is a function of the extent to which stresses are frozen into them on molding. The kind and amount of plasticizer included in the material to be molded may be varied to minimize the amount of these stresses. Methods of obtaining fundamental information about polymer–plasticizer systems from simple measurements of viscosity and osmotic pressure are suggested in this paper, and some results for cellulose derivatives are given.
Cellulose acetate esters containing amino nitrogen
Authors: Gardner Thomas S. 
Published: April 2003

AbstractNitrogen was introduced into cellulose acetate by the incorporation of amino acid groups. Some of the mixed esters were soluble in organic solvents. Cast films were examined for dyeing properties with wool‐type dyes. Many of the mixed esters containing above 1% nitrogen dyed well with xylene brilliant blue, a typical wool‐type dye, Mixed cellulose acetate esters were synthesized containing glycine, dl‐α‐alanine, β‐alanine, and α‐isoaminobutyric, d‐glutamic, and p‐aminobenzoic acids. The amino groups were protected by acetylation prior to use. The N‐acetyl amino acids were treated with cellulose diacetate in dioxane solution containing chloroacetic anhydride and magnesium perchlorate as impellor and catalyst, respectively. Cellulose acetate metanilate was prepared by use of the aminosulfo acid chloride. An attempt was made to prepare 6‐aminocellulose by the reaction of aqueous ammonia, and also sodamide in liquid ammonia on 6‐iodotosylcellulose acetate. Only traces of nitrogen were introduced by this procedure and the recovered products showed signs of extreme degradation.
Density of cellulose fibers. I. Introduction and experiments on the penetration of liquids into dry cellulose
Authors: Hermans P. H. , Vermaas D. 
Published: April 2003

AbstractIn this paper it is emphasized that density is a typically macroscopic concept which cannot be transferred to small particles or bodies with small pores. This fact has not been duly accounted for in earlier work on the density of cellulose fibers. The usual interpretation of density determinations in various media is criticized and the point of view that cellulose fibers should be considered as porous bodies is dropped. The pore system occurring in native fibers is coarse enough not to interfere with density determinations in indifferent organic liquids.It is shown experimentally that even substances like water and glycerol penetrate very slowly into dry cellulose and that indifferent organic liquids do not penetrate at all. In the experiments with water vapor a new phenomenon, the heterogeneous course of absorption, is observed, giving rise to sharp microscopically visible boundary lines between the wet and the dry portion of the fiber.
Statistical behavior of the single chain molecule and its relation to the statistical behavior of assemblies consisting of many chain molecules
Authors: Kuhn Werner , Grün Franz 
Published: April 2003

AbstractThe molecules of high‐molecular substances, for instance, those present in rubber, can be treated statistically in two ways. On the one hand, these molecules are such complicated structures that it is possible to attribute a separate entropy and free energy to each giant molecule. On the other hand, solutions of high‐molecular substances represent systems in which the single chain molecule is the elementary particle, and to which statistical considerations and concepts such as entropy and free energy can be applied. Depending upon the parameter considered, the same chain molecule must sometimes be treated as a complicated system and at other times as an elementary particle. The problems originating from the simultaneous existence of two stages in the statistical treatment are examined. It is shown that the entropy of an assembly of many chain molecules is not simply equal to the sum of the entropies of the separate chain molecules. This becomes apparent particularly when determining the distribution function with respect to a particular parameter (e.g., distance between the two end points of a molecule) from a statistical consideration of the single molecule on the one hand, and from a consideration of an assembly of identical molecules on the other hand. The relations between entropy and free energy of the individual particle and the a priori probabilities on which the treatment of an assembly is to be based are explained. It is further shown that the same particle can give rise to a macroscopic phenomenon in two ways and to approximately the same extent: first, as a complicated system, and second, as an element in a large assembly of identical particles. This applies in particular to the elastic retractive force and to the strain birefringence in rubber and related substances.
Relation between molecular weight and intrinsic viscosity for polymethyl methacrylate
Authors: Baxendale J. H. , Bywater S. , Evans M. G. 
Published: April 2003

AbstractThe chain lengths of polymethyl methacrylates prepared with ferrous ion–hydrogen peroxide as the initiating system are consistent with the scheme advanced for the mechanism of the polymerization. The relation between intrinsic viscosity in benzene and molecular weight for fractionated polymethyl methacrylate has been determined and leads to the equation: n = 2.81 × 103 [η]C6H61.32. This equation agrees very well with the data of Schulz, provided that the correct method of extrapolating the osmotic pressures to zero concentration is used. Using the relationship between [η]C6H6 and [η]CHCl3 obtained experimentally, the relation between n and [η]CHCl3 (at 20°C.) is: n = 1.81 l3 × 103[η]CHCl31.22.
Modern views on the chemistry of vulcanization changes. I. Nature of the reaction between sulfur and olefins
Authors: Farmer E. Harold , Shipley F. W. 
Published: April 2003

AbstractWhatever additional factors may be concerned in the production of good vulcanizates from natural rubber by the action of sulfur, there is no doubt that the action of sulfur on olefinic materials in general at the ordinary vulcanization temperature is a chemical one, the primary course of which is determined largely by the constitution of the olefin, and hence may be profitably studied by experimentation with olefins of different unsaturation patterns. Unaccelerated reaction between sulfur and simple monoolefins leads almost exclusively to cross linking of the separate olefin molecules, mostly in pairs, by groups of sulfur atoms. When, however, two or more olefinic units occur in the same molecule, as in the disoprenic hydrocarbons, intramolecular cross linking, i.e., cyclization, at once becomes possible, and the result of sulfur action consists partly in the cross linking of separate molecules as with the monoolefins, but largely in cyclization of the individual olefinic chains, thereby forming sulfur‐containing rings. These changes entail a certain loss of unsaturation, from which deductions can be made as to the mechanism of the reaction.
Modern views on the chemistry of vulcanization changes. II. Role of hydrogen sulfide
Authors: Naylor Ralph F. 
Published: April 2003

AbstractHydrogen sulfide has often been thought to play an important role in the sulfur vulcanization of natural rubber. A study has therefore been made of the reaction of hydrogen sulfide with olefins, including polyisoprenes, with special reference to the capacity of the reagent to react with olefins in the presence of free sulfur. Comparison of the products so obtained with those derived (a) by light‐catalyzed reaction of hydrogen sulfide and (b) by reaction of free sulfur with polyisoprenes has greatly assisted the understanding of the course of sulfur reaction in vulcanization processes.
Elastic properties of textile yarns, represented with the aid of a mechanical model
Authors: Vreedenberg H. A. 
Published: April 2003

AbstractA series of experiments on the elastic behavior of various textile materials was carried out. All results are described with the aid of a mechanical model. For this purpose it is necessary to introduce the possibility of a blockade of a part of the model. The elastic properties are characterized by the values of seven independent fundamental constants of the model. The value of one of these constants associated with the blockade can be determined experimentally in a direct way; it is found to be independent of the moisture content. The most important properties of the model correspond with the molecular image of Hermans.
Deformation mechanism of cellulose gels. I. Present status of the problem
Authors: Hermans P. H. 
Published: April 2003

AbstractA brief outline is given of the present status of research on the problem of the deformation mechanism of cellulose gels. Emphasis is placed on the prevailing idea of a molecular network structure and recognition of the existence of an intimate relationship between the phenomena of deformation and those of swelling. In these respects the problems involved in cellulose research seem to show a marked convergence with those which emerge from recent developments in rubber research. The principle of Kratky's theory of “affined transformation” and the experiments carried out by this author in order to verify his theory are discussed briefly.