bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization of paired helical filaments by scanning transmission electron microscopy
Authors: Ksiezak‐Reding Hanna , Wall Joseph S. 
Published: August 2005

AbstractPaired helical filaments (PHFs) are abnormal twisted filaments composed of hyperphosphorylated tau protein. They are found in Alzheimer's disease and other neurodegenerative disorders designated as tauopathies. They are a major component of intracellular inclusions known as neurofibrillary tangles (NFTs). The objective of this review is to summarize various structural studies of PHFs in which using scanning transmission electron microscopy (STEM) has been particularly informative. STEM provides shape and mass per unit length measurements important for studying ultrastructural aspects of filaments. These include quantitative comparisons between dispersed and aggregated populations of PHFs as well as comparative studies of PHFs in Alzheimer's disease and other neurodegenerative disorders. Other approaches are also discussed if relevant or complementary to studies using STEM, e.g., application of a novel staining reagent, Nanovan. Our understanding of the PHF structure and the development of PHFs into NFTs is presented from a historical perspective. Others goals are to describe the biochemical and ultrastructural complexity of authentic PHFs, to assess similarities between authentic and synthetic PHFs, and to discuss recent advances in PHF modeling. Microsc. Res. Tech. 67:126–140, 2005. © 2005 Wiley‐Liss, Inc.
Amyloid‐β aggregates formed at polar–nonpolar interfaces differ from amyloid‐β protofibrils produced in aqueous buffers
Authors: Nichols Michael R. , Moss Melissa A. , Reed Dana Kim , Hoh Jan H. , Rosenberry Terrone L. 
Published: August 2005

AbstractThe deposition of aggregated amyloid‐β (Aβ) peptides in the brain as senile plaques is a pathological hallmark of Alzheimer's disease (AD). Several lines of evidence indicate that fibrillar and, in particular, soluble aggregates of these 40‐ and 42‐residue peptides are important in the etiology of AD. Recent studies also stress that amyloid aggregates are polymorphic and that a single polypeptide can fold into multiple amyloid conformations. Here we review our recent reports that Aβ(1‐40) in vitro can form soluble aggregates with predominant β‐structures that differ in stability and morphology. One class of aggregates involved soluble Aβ protofibrils, prepared by vigorous overnight agitation of monomeric Aβ(1‐40) in low ionic strength buffers. These aggregates were quite stable and disaggregated to only a limited extent on dilution. A second class of soluble Aβ aggregates was generated at polar–nonpolar interfaces. Aggregation in a two‐phase system of buffer over chloroform occurred more rapidly than in buffer alone. In buffered 2% hexafluoroisopropanol (HFIP), microdroplets of HFIP were formed and the half‐time for aggregation was less than 10 minutes. Like Aβ protofibrils, these interfacial aggregates showed increased thioflavin T fluorescence and were rich in β‐structure by circular dichroism. However, electron microscopy and atomic force microscopy revealed very different morphologies. The HFIP aggregates formed initial globular clusters that progressed over several days to soluble fibrous aggregates. When diluted out of HFIP these aggregates initially were very unstable and disaggregated completely within 2 minutes. However, their stability increased as they progressed to fibers. It is important to determine whether similar interfacial Aβ aggregates are produced in vivo. Microsc. Res. Tech. 67:164–174, 2005. © 2005 Wiley‐Liss, Inc.
Characterization of Alzheimer paired helical filaments by electron microscopy
Authors: Hernández Félix , Engel Tobias , Gómez‐Ramos Alberto , Pérez Mar , Avila Jesús 
Published: August 2005

AbstractWe show how electron microscopy can be used to answer several critical issues in neurodegenerative disorders that course with the formation of aberrant filamentous structures. Thus, electron microscopy is a useful technique to study in vitro assembly of pathogenic proteins, to map the regions involved in filament formation, as well as to detect by immunoelectron microscopy which proteins bind to the filaments. Furthermore, electron microscopy is the main technique used to discover if an animal model develops fibrillar pathology and if those filaments are similar to those found in human patients. This review focuses on Alzheimer's disease and related tauopathies, although similar studies have been done with other neurodegenerative disorders as, for example, Huntington's disease. Microsc. Res. Tech. 67:121–125, 2005. © 2005 Wiley‐Liss, Inc.
Paired helical filaments (PHFs) are a family of single filament structures with a common helical turn period: Negatively stained PHF imaged by TEM and measured before and after sonication, deglycosylation, and dephosphorylation
Authors: Ruben George C. , Wang Jian‐zhi , Iqbal Khalid , Grundke‐Iqbal Inge 
Published: August 2005

AbstractIsolated paired helical filaments (PHFs) were visualized on glutaraldehyde vapor‐treated thin ∼10‐nm thick indirect carbon films using high‐resolution transmission electron microscopy (TEM) and the negative stain, phosphotungstate acid (PTA) at near neutral pH of 6.8. PHF preparations were prepared with and without 1 minute of sonication. These same PHF were also deglycosylated with endoglycosidase F/N‐glycosidase F for 1 hour or the PHF were dephosphorylated with PP‐2A for 1 hour. The negatively stained PHF filaments were quantitatively studied by measuring their wide regions (W) their thin regions (T) and their helical turn period (L) and these separate parameters were averaged for each filament. In the unsonicated PHF preparation there were PHF, cylindrical filaments with periodic thin regions (CF‐PT), cylindrical filaments (CF), as well as 2.0‐nm tau polymer‐like filaments. The CF‐PT were characterized by W, T, and L measurements and the CF were characterized by diameter measurements. The paired helical filament model proposed by Kidd (1963, Nature 197:192–193) of two ∼10 nm filaments twisting around each other every ∼80 nm with a thin region of 10 nm and a wide region of 25 nm does not correspond to the PHF structures found. None of the PHF we observed were composed of a pair of filaments and all of the PHF appear to be a single filament. The wide regions ranged from 12.5–27 nm and the thin regions ranged from 4.5–12.3 nm. The helical turn periods ranged from 76–85 nm and were generally about 80 nm. Only the helical turn period of ∼80 nm was a common property of the whole family of PHF structures. The CF‐PT appear to be a PHF precursor filament. Deglycosylation of the PHF and CF‐PT reduced their sizes by 0.5–0.6 nm and 0.7–1.0 nm, respectively, and the right‐hand helicity of the PHF was lost after deglycosylation. Dephosphorylation with PP‐2A reduced the PHF wide regions by 6.0 nm and the thin regions by 2.6 nm. Microsc. Res. Tech. 67:175–195, 2005. © 2005 Wiley‐Liss, Inc.
Alzheimer paired helical filaments (PHFs) studied by high‐resolution TEM: What can vertical Pt‐C replication tell us about the organization of the pronase‐digested PHF core?
Authors: Ruben George C. , Novak Michal , Edwards Patricia C. , Iqbal Khalid 
Published: August 2005

AbstractUntreated paired helical filaments (PHFs) and pronase‐digested PHF‐core filaments were stereoscopically imaged with a freeze‐drying vertical platinum‐carbon replication preparation method for TEM. The untreated PHF have an average wide region (W) = 22.8 ± 2.4 nm, a narrow region (T) = 10.6 ± 1.7 nm, and a helical turn period (L) = 78.6 ± 13.4. The surfaces of the untreated PHF's fuzzy coat appears disorganized. The widths of the pronase‐treated PHF‐core filaments were significantly reduced (Wd = 14.8 ± 1.2 nm, Td = 5.7 ± 1.0 nm, and Ld = 75.4 ± 17 nm). The surfaces of the untreated PHF contained ∼1.1 nm strands, the same size as tau monomer (∼1.0 nm). The pronase‐digested PHF cores mostly contained ∼1.6 ± 0.3 nm strands although strand diameters ranged from 0.6–2.5 nm. The strands sometimes appear to be wrapped around the filament axis; less often, they appear to be roughly parallel to the PHF axis, and otherwise appear to be randomly oriented. Images of pronase‐digested PHF core images are discussed in relation to the core's biochemical composition, its proposed beta structure, and structural subunit models. Images of the untreated and the pronase‐digested PHF support a helical ribbon morphology. Microsc. Res. Tech. 67:196–209, 2005. © 2005 Wiley‐Liss, Inc.
Retrospective motion compensation using variable‐density spiral trajectories
Authors: Leung General , Plewes Donald B. 
Published: August 2005

AbstractPurposeTo develop a method of retrospectively correcting for motion artifacts using a variable‐density spiral (VDS) trajectory.Materials and MethodsEach VDS interleaf was designed to adequately sample the same center region of k‐space. This central overlapping region can then be used to measure rigid body motion between the acquisition of each VDS interleaf. By applying appropriate phase shifts and rotations of the k‐space data, rigid body motion artifacts can be removed, resulting in images with less motion corruption.ResultsBoth phantom and volunteer experiments are shown, demonstrating the technique's ability to further reduce artifacts in images acquired with an already motion‐resistant acquisition trajectory. Registration accuracy is highly dependent on the trajectory design parameters. This space was explored to find an optimal design of VDS trajectories for motion compensation.ConclusionUsing appropriately designed VDS trajectories, residual motion artifacts can be significantly reduced by retrospectively correcting for in‐plane rigid body motion. An overlapping region of approximately 8% of the central region of k‐space and approximately 70 interleaves were found to be near‐optimal parameters for retrospective correction using VDS trajectories. J. Magn. Reson. Imaging 2005. © 2005 Wiley‐Liss, Inc.
Detection of acute renal ischemia in swine using blood oxygen level‐dependent magnetic resonance imaging
Authors: Alford Sara K. , Sadowski Elizabeth A. , Unal Orhan , Polzin Jason A. , Consigny Daniel W. , Korosec Frank R. , Grist Thomas M. 
Published: August 2005

AbstractPurposeTo determine the feasibility and sensitivity of blood oxygen level‐dependent (BOLD) magnetic resonance imaging (MRI) to detect acute renal ischemia, using a swine model, and to present the causes of variability and assess techniques that minimize variability introduced during data analysis.Materials and MethodsBOLD MRI was performed in axial and coronal planes of the kidneys of five swine. Color R2* maps were calculated and mean R2* values and 95% confidence intervals (CIs) for the cortex and medulla were determined for baseline, renal artery occlusion and reperfusion conditions. Paired Student's t‐tests were used to determine significance.ResultsMean R2* measurements increased from baseline during renal artery occlusion in the cortex (axial, 13.8–24.6 second−1; coronal, 14.4–24.7 second−1) and medulla (axial, 19.3–32.2 second−1; coronal, 20.1–30.7 second−1). These differences were significant for both the cortex (axial, P < 0.04; coronal, P < 0.005) and medulla (axial, P < 0.02; coronal, P < 0.0005). No significant change was observed in the contralateral kidney.ConclusionR2* values were significantly higher than baseline for medulla and cortex during renal artery occlusion. More variability exists in R2* measurements in the medulla than the cortex and in the axial than the coronal plane. J. Magn. Reson. Imaging 2005. © 2005 Wiley‐Liss, Inc.
Functional magnetic resonance imaging activation detection: Fuzzy cluster analysis in wavelet and multiwavelet domains
Authors: Jahanian Hesamoddin , Soltanian‐Zadeh Hamid , Hossein‐Zadeh Gholam‐Ali 
Published: August 2005

AbstractPurposeTo present novel feature spaces, based on multiscale decompositions obtained by scalar wavelet and multiwavelet transforms, to remedy problems associated with high dimension of functional magnetic resonance imaging (fMRI) time series (when they are used directly in clustering algorithms) and their poor signal‐to‐noise ratio (SNR) that limits accurate classification of fMRI time series according to their activation contents.Materials and MethodsUsing randomization, the proposed method finds wavelet/multiwavelet coefficients that represent the activation content of fMRI time series and combines them to define new feature spaces. Using simulated and experimental fMRI data sets, the proposed feature spaces are compared to the cross‐correlation (CC) feature space and their performances are evaluated. In these studies, the false positive detection rate is controlled using randomization. To compare different methods, several points of the receiver operating characteristics (ROC) curves, using simulated data, are estimated and compared.ResultsThe proposed features suppress the effects of confounding signals and improve activation detection sensitivity. Experimental results show improved sensitivity and robustness of the proposed method compared to the conventional CC analysis.ConclusionMore accurate and sensitive activation detection can be achieved using the proposed feature spaces compared to CC feature space. Multiwavelet features show superior detection sensitivity compared to the scalar wavelet features. J. Magn. Reson. Imaging 2005. © 2005 Wiley‐Liss, Inc.
The impact of partial‐volume effects in dynamic susceptibility contrast magnetic resonance perfusion imaging
Authors: Chen Jean J. , Smith Michael R. , Frayne Richard 
Published: August 2005

AbstractPurposeTo demonstrate the degree of the cerebral blood flow (CBF) estimation bias that could arise from distortion of the arterial input function (AIF) as a result of partial‐volume effects (PVEs) in dynamic susceptibility contrast (DSC) magnetic resonance imaging (MRI).Materials and MethodsA model of the volume fraction an artery occupies in a voxel was devised, and a mathematical relationship between the amount of PVE and the measured baseline MR signal intensity was derived. Based on this model, simulation studies were performed to assess the impact of PVE on CBF. Furthermore, the effectiveness of linear PVE compensation approaches on the concentration function was investigated.ResultsSimulation results showed a nonlinear relationship between PVE and the resulting CBF measurement error. In addition to AIF underestimation, PVE also causes distortions of AIF frequency characteristics, leading to CBF errors varying with mean transit time (MTT). An uncorrected AIF measured at a voxel with a partial‐volume fraction of ≤50% could produce a CBF overestimation of more than fourfold. Linear compensation of the concentration curves did not produce correct CBF estimates.ConclusionPVE can induce significant CBF estimation biases. In addition, the MTT dependence of CBF accuracy raises doubts of the validity of adopting a single cross‐calibration factor (i.e., setting normal white matter to 22 mL minute−1 (100 g)−1) to obtain CBF values with absolute units. The impact of PVE may be reduced by decreasing the maximum arterial signal drop in the perfusion images. To correct the AIF distortions introduced by PVE, the nonlinear relationship between the impact of PVE on MR signal intensity and contrast concentration function must be considered. J. Magn. Reson. Imaging 2005. © 2005 Wiley‐Liss, Inc.
Comparison of Gd [DTPA‐bis (2‐aminoethoxy) ethane] polymeric contrast agent with gadodiamide injection for interstitial MR lymphography: Experimental study with rabbits
Authors: Zhou Zhengyang , Guo Jian , Yu Haiping , Zhu Bin , Liu Changjian , Jiang Xiqun , Zhang Ming , Chen Junkun 
Published: August 2005

AbstractPurposeTo compare the differences between macromolecular and small molecular contrast agents in interstitial magnetic resonance (MR) lymphography.Materials and MethodsIn two groups of rabbits (N = 12 each), 0.5‐mL volumes of 0.5 M and 0.1 M gadodiamide, respectively, were injected subcutaneously into the dorsal feet of both hind legs. After a 24‐hour interval, 0.5 mL of Gd [DTPA‐bis (2‐aminoethoxy) ethane] polymeric contrast agent (Gd‐poly‐DTPA‐EOEA) injection (0.1 M) was injected into the same sites in each rabbit. T1‐weighted three‐dimensional gradient‐echo and maximum intensity projection (MIP) images were obtained before and after the administration of each agent. The nodal maximum short‐axis diameter (MSAD) and signal‐to‐noise ratio (SNR) at each time point were measured. Postmortem measurements of nodal MSADs were also performed. The nodal MSAD measurements obtained by MR lymphography were compared with the postmortem measurements. As an additional control experiment, six rabbits received a subcutaneous injection of 0.5 mL of 0.1 M gadodiamide at the same sites as those described above. This procedure was repeated after a 24‐hour interval to determine whether the first injected gadodiamide had any effect on the performance of the subsequently injected agent, by comparing the differences in nodal MSADs obtained by MR lymphography after each injection.ResultsGd‐poly‐DTPA‐EOEA showed a significantly longer enhancement plateau compared to gadodiamide. In comparison with postmortem measurements, nodal measurements by MR lymphography with Gd‐poly‐DTPA‐EOEA at the peak‐enhancement phase revealed no significantly different MSADs (P > 0.05), whereas nodal measurements by MR lymphography with gadodiamide showed significantly smaller MSADs (P < 0.05). A comparison of the nodal MSADs measured in two gadodiamide‐enhanced MR examinations after the 24‐hour interval showed no significant difference (P > 0.05).ConclusionInterstitial MR lymphography with polymeric Gd‐poly‐DTPA‐EOEA enhancer enables more sufficient and reliable visualization of lymph nodes compared to small molecular gadodiamide. J. Magn. Reson. Imaging 2005. © 2005 Wiley‐Liss, Inc.
Quantitative analysis of regional airways obstruction using dynamic hyperpolarized 3He MRI—Preliminary results in children with cystic fibrosis
Authors: Koumellis Panos , van Beek Edwin J.R. , Woodhouse Neil , Fichele Stan , Swift Andrew J. , Paley Martyn N.J. , Hill Catherine , Taylor Chris J. , Wild Jim M. 
Published: August 2005

AbstractPurposeTo investigate regional airways obstruction in patients with cystic fibrosis (CF) with quantitative analysis of dynamic hyperpolarized (HP) 3He MRI.Materials and MethodsDynamic radial projection MRI of HP 3He gas was used to study respiratory dynamics in a group of eight children with CF. Signal kinetics in a total of seven regions of interest (ROIs; three in each lung, and one in the trachea) were compared with the results of spirometric pulmonary function tests (PFTs). The tracheal signal intensity was used as a form of “input function” to normalize for input flow effects.ResultsA pattern of low flow rate in the upper lobes was observed. When the flow measurements from the peripheral ROIs were averaged to obtain an index of flow in the peripheral lung, a good correlation was found (P = 3.74 × 10−5) with the forced expired volume in one second (FEV1).ConclusionThese results suggest that a quantitative measurement of localized airways obstruction in the early stages of CF may be obtained from dynamic 3He MRI by using the slope of the signal rise as a measure of air flow into the peripheral lung. This study also demonstrates that children can cooperate well with the 3He MRI technique. J. Magn. Reson. Imaging 2005. © 2005 Wiley‐Liss, Inc.
Combined T1‐T2 mapping of human femoro‐tibial cartilage with turbo‐mixed imaging at 1.5T
Authors: Van Breuseghem Iwan , Palmieri Francesco , Peeters Ronald R. , Maes Frederik , Bosmans Hilde T.C. , Marchal Guy J. 
Published: August 2005

AbstractPurposeTo evaluate the influence of Gd‐DTPA on cartilage T2 mapping using turbo‐mixed (tMIX) imaging, and to show the possible usefulness of the tMIX technique for simultaneously acquiring T1 and T2 information in cartilage.Materials and MethodsTwenty volunteers underwent MRI of the knee using the tMIX sequence before and after gadolinium administration. T1 and T2 maps were calculated. The mean T1 was determined on the pre‐ and postcontrast T1 maps. T2 relaxation values before and after gadolinium administration were statistically analyzed.ResultsThe obtained relaxation values are in correspondence with previously published data. The mean T1 before gadolinium administration was 449 msec ± 34.2 msec (SD), and after gadolinium administration it was 357 msec ± 55.8 msec (SD). The postcontrast T1 relaxation range was 221.5–572.8 msec. The mean T2 of the precontrast T2 maps was 34.2 msec ± 3.1 msec (SD), and the mean T2 of the postcontrast T2 maps was 32.5 msec ± 3.1 msec (SD). These are statistically significant different values. A correction for the postcontrast T2 values, using a back‐calculation algorithm, yielded a 98% correlation with the precontrast T2 values.ConclusionThe absolute difference of pre‐ and postcontrast T2 is very small and is ruled out using the back‐calculation algorithm. Combined T1‐T2 tMIX cartilage mapping is a valuable alternative for separate T1 and T2 cartilage mapping. J. Magn. Reson. Imaging 2005. © 2005 Wiley‐Liss, Inc.
Electron ionization and methane chemical ionization mass spectrometry study of some 2,2‐disubstituted 1,3‐dioxolanes, 1,3‐dithiolanes, 1,3‐oxathiolanes and 1,3‐dioxanes. Gas‐phase lactone and thiolactone formation
Authors: Pakarinen Jaana M. H. , Kolehmainen Jaana , Yrjölä Sari , Vainiotalo Pirjo 
Published: August 2005

AbstractThe electron ionization and methane chemical ionization mass spectra of some 2,2‐disubstituted 1,3‐dioxolanes, 1,3‐dithiolanes and 1,3‐oxathiolanes were studied. Especially, the effect of the length of the side chain in ring position 2 of these compounds and the ease of formation of possible lactone/thiolactone ion as a fragmentation product were examined. In addition, two 2,2‐disubstituted 1,3‐dioxanes were studied to see the effect of the bigger ring size. The formation of lactone ions was more favorable under methane chemical ionization than under electron ionization conditions. The structures of fragment ions and the ions generated from model compounds were carefully studied using both high‐ and low‐energy collision‐induced dissociation. Also ab initio molecular orbital calculations up to the HF/6–31G** level of theory for protonated 2‐methyl‐2‐propanoic acid ethyl ester of 1,3‐dioxolane, 1,3‐oxathiolane and 1,3‐dithiolane and for two isomeric bicyclic ions were carried out. The theoretical results obtained favor the formation of the lactone ion. Copyright © 2005 John Wiley & Sons, Ltd.
Analysis of molecular weight distributions of styrene‐methyl methacrylate copolymers using size exclusion chromatography data
Authors: Matusinović Zvonimir , Tomić Tatjana , Šegudović Nikola , Rogošić Marko 
Published: August 2005

AbstractSize exclusion chromatography (SEC) is a common method for the determination of molecular weight distributions (MWD) of polymers. Using appropriate normalization procedures, MWD data may be put in a form suitable for the description by different theoretical distribution functions. In this paper such a procedure is described and applied to a model system. Statistical copolymers of styrene and methyl methacrylate (SMMA) of different compositions were synthesized by radical copolymerization in a batch isothermal reactor with toluene as solvent and azobisisobutyronitrile as initiator. Copolymer MWDs were obtained by SEC and average copolymer composition by elemental analysis. MWDs of SMMA copolymers were correlated with the lognormal, Flory, Schulz, and Tung theoretical function. The best match between experimental and calculated data was obtained by the Schulz distribution. The α‐parameter of Schulz's function was related to the average molecular weight and showed its maximum at the midpoint of the copolymer composition range, in connection with the observed minimal copolymerization rate. The variation of the b‐parameter was found to be less pronounced; the parameter was related to the polydispersity index. This feature indicated that there was no significant change in the copolymerization reaction mechanism throughout the entire copolymer composition range.