bluuebunny/crossref_metadata_2025_split huggingface dataset:
MR tracking of transplanted cells with “positive contrast” using manganese oxide nanoparticles
Authors: Gilad Assaf A. , Walczak Piotr , McMahon Michael T. , Na Hyon Bin , Lee Jung Hee , An Kwangjin , Hyeon Taegwhan , van Zijl Peter C.M. , Bulte Jeff W.M. 
Published: June 2008

AbstractRat glioma cells were labeled using electroporation with either manganese oxide (MnO) or superparamagnetic iron oxide (SPIO) nanoparticles. The viability and proliferation of SPIO‐labeled cells (1.9 mg Fe/ml) or cells electroporated with a low dose of MnO (100 μg Mn/ml) was not significantly different from unlabeled cells; a higher MnO dose (785 μg Mn/ml) was found to be toxic. The cellular ion content was 0.1–0.3 pg Mn/cell and 4.4 pg Fe/cell, respectively, with cellular relaxivities of 2.5–4.8 s−1 (R1) and 45–84 s−1 (R2) for MnO‐labeled cells. Labeled cells (SPIO and low‐dose MnO) were each transplanted in contralateral brain hemispheres of rats and imaged in vivo at 9.4T. While SPIO‐labeled cells produced a strong “negative contrast” due to the increase in R2, MnO‐labeled cells produced “positive contrast” with an increased R1. Simultaneous imaging of both transplants with opposite contrast offers a method for MR “double labeling” of different cell populations. Magn Reson Med 60:1–7, 2008. © 2008 Wiley‐Liss, Inc.
NMR probes for measuring magnetic fields and field dynamics in MR systems
Authors: De Zanche Nicola , Barmet Christoph , Nordmeyer‐Massner Jurek A. , Pruessmann Klaas P. 
Published: June 2008

AbstractHigh‐resolution magnetic field probes based on pulsed liquid‐state NMR are presented. Static field measurements with an error of 10 nanotesla or less at 3 tesla are readily obtained in 100 ms. The further ability to measure dynamic magnetic fields results from using small (∼1 μL) droplets of MR‐active liquid surrounded by susceptibility‐matched materials. The consequent high field homogeneity allows free induction decay signals lasting 100 ms or more to be readily achieved. The small droplet dimensions allow the magnetic field to be measured even in the presence of large gradients. Highly sensitive detection yields sufficient SNR to follow the relevant field evolution without signal averaging and at bandwidths up to hundreds of kHz. Transient, nonreproducible effects and drifts are thus readily monitored. The typical application of k‐space trajectory mapping has been demonstrated. Potential further applications include characterization, tuning, and maintenance of gradient systems as well as the mapping of the static field distribution of MRI magnets. Connection of the probes to a standard MR spectrometer is similar to that used for imaging coils. Magn Reson Med 60:176–186, 2008. © 2008 Wiley‐Liss, Inc.
Nuclear magnetic resonance‐based metabolomics predicts exercise‐induced ischemia in patients with suspected coronary artery disease
Authors: Barba Ignasi , de León Gustavo , Martín Eva , Cuevas Antonio , Aguade Santiago , Candell‐Riera Jaume , Barrabés José A. , Garcia‐Dorado David 
Published: June 2008

AbstractThe purpose of this study was to develop a 1H‐nuclear magnetic resonance metabolomic approach capable of predicting the occurrence of exercise‐induced ischemia in patients with suspected coronary artery disease and to identify the metabolite patterns that contribute most importantly to the prediction. In 31 patients with suspected effort angina and without previous myocardial infarction, serum was obtained just prior to a stress single‐photon emission computed tomography. Serum NMR spectra were acquired with pulse‐and‐acquire and T2‐edited sequences. The region between 0.50 and 4.25 ppm was used for analysis. Twenty‐two patients had reversible myocardial perfusion defects and nine did not. Both groups had similar age and clinical profile, except for more smokers and diabetics in the ischemia group, and attained a similar peak heart rate. The best separation was achieved with long T2‐edited spectra, 84% of patients being correctly classified based on the partial least square discriminant analysis. The main contributors to discrimination were lactate, glucose, as well as methyl and methylene moieties of lipids and long‐chain amino acids. Metabolomic analysis of serum can predict exercise‐inducible ischemia in patients with suspected coronary artery disease. This capability could be useful in screening and risk stratification of patients with coronary risk factors. Magn Reson Med 60:27–32, 2008. © 2008 Wiley‐Liss, Inc.
Serial in vivo positive contrast MRI of iron oxide‐labeled embryonic stem cell‐derived cardiac precursor cells in a mouse model of myocardial infarction
Authors: Mani Venkatesh , Adler Eric , Briley‐Saebo Karen C. , Bystrup Anne , Fuster Valentin , Keller Gordon , Fayad Zahi A. 
Published: June 2008

AbstractMyocardial regeneration with stem‐cell transplantation is a possible treatment option to reverse deleterious effects that occur after myocardial infarction. Since little is known about stem cell survival after transplantation, developing techniques for “tracking” cells would be desirable. Iron‐oxide‐labeled stem cells have been used for in vivo tracking using MRI but produce negative contrast images that are difficult to interpret. The aim of the current study was to test a positive contrast MR technique using reduced z‐gradient rephasing (GRASP) to aid in dynamically tracking stem cells in an in vivo model of mouse myocardial infraction. Ferumoxides and protamine sulfate were complexed and used to magnetically label embryonic stem cell‐derived cardiac‐precursor‐cells (ES‐CPCs). A total of 500,000 ES‐CPCs were injected in the border zone of infarcted mice and MR imaging was performed on a 9.4T scanner using T‐GRE sequences (negative contrast) and positive contrast GRASP technique before, 24 hours, and 1 week after ES‐CPC implantation. Following imaging, mice were sacrificed for histology and Perl's staining was used to confirm iron within myocardium. Good correlation was observed between signal loss seen on conventional T images, bright areas on GRASP, and the presence of iron on histology. This demonstrated the feasibility of in vivo stem cell imaging with positive contrast MRI. Magn Reson Med 60:73–81, 2008. © 2008 Wiley‐Liss, Inc.
Manganese‐enhanced MRI of the mouse auditory pathway
Authors: Watanabe Takashi , Frahm Jens , Michaelis Thomas 
Published: June 2008

AbstractFunctional mapping of the lateral lemniscus and the superior olivary complex as part of the auditory pathway was accomplished for the first time in mice in vivo using manganese‐enhanced MRI (2.35T, 3D FLASH, 117 μm isotropic resolution). These and other auditory centers in the brainstem presented with pronounced signal enhancements after systemic administration of manganese chloride when animals were exposed to acoustic stimuli for 48 hr, but not when kept in a quiet environment. The results indicate an activation‐dependent accumulation of manganese in the neural circuit composed of the cochlear nucleus, the superior olivary complex, the lateral lemniscus, and the inferior colliculus. The marked enhancement of the lateral lemniscus suggests that the stimulus‐related accumulation of manganese reflects not only a regional uptake from extracellular fluid but also a concurrent delivery by axonal transport within the auditory system. Magn Reson Med 60:210–212, 2008. © 2008 Wiley‐Liss, Inc.
Quantification of choline‐ and ethanolamine‐containing metabolites in human prostate tissues using 1H HR‐MAS total correlation spectroscopy
Authors: Swanson Mark G. , Keshari Kayvan R. , Tabatabai Z. Laura , Simko Jeffry P. , Shinohara Katsuto , Carroll Peter R. , Zektzer Andrew S. , Kurhanewicz John 
Published: June 2008

AbstractA fast and quantitative 2D high‐resolution magic angle spinning (HR‐MAS) total correlation spectroscopy (TOCSY) experiment was developed to resolve and quantify the choline‐ and ethanolamine‐containing metabolites in human prostate tissues in ≈1 hr prior to pathologic analysis. At a 40‐ms mixing time, magnetization transfer efficiency constants were empirically determined in solution and used to calculate metabolite concentrations in tissue. Phosphocholine (PC) was observed in 11/15 (73%) cancer tissues but only 6/32 (19%) benign tissues. PC was significantly higher (0.39 ± 0.40 mmol/kg vs. 0.02 ± 0.07 mmol/kg, z = 3.5), while ethanolamine (Eth) was significantly lower in cancer versus benign prostate tissues (1.0 ± 0.8 mmol/kg vs. 2.3 ± 1.9 mmol/kg, z = 3.3). Glycerophosphocholine (GPC) (0.57 ± 0.87 mmol/kg vs. 0.29 ± 0.26 mmol/kg, z = 1.2), phosphoethanolamine (PE) (4.4 ± 2.2 mmol/kg vs. 3.4 ± 2.6 mmol/kg, z = 1.4), and glycerophosphoethanolamine (GPE) (0.54 ± 0.82 mmol/kg vs. 0.15 ± 0.15 mmol/kg, z = 1.8) were higher in cancer versus benign prostate tissues. The ratios of PC/GPC (3.5 ± 4.5 vs. 0.32 ± 1.4, z = 2.6), PC/PE (0.08 ± 0.08 vs. 0.01 ± 0.03, z = 3.5), PE/Eth (16 ± 22 vs. 2.2 ± 2.0, z = 2.4), and GPE/Eth (0.41 ± 0.51 vs. 0.06 ± 0.06, z = 2.6) were also significantly higher in cancer versus benign tissues. All samples were pathologically interpretable following HR‐MAS analysis; however, degradation experiments showed that PC, GPC, PE, and GPE decreased 7.7 ± 2.2%, while Cho+mI and Eth increased 18% in 1 hr at 1°C and a 2250 Hz spin rate. Magn Reson Med 60:33–40, 2008. © 2008 Wiley‐Liss, Inc.
Kalman filtering for real‐time navigator processing
Authors: Spincemaille Pascal , Nguyen Thanh D. , Prince Martin R. , Wang Yi 
Published: June 2008

AbstractNavigator echoes are used in high‐resolution cardiac MRI for tracking physiological motion to suppress motion artifacts. Alternatives to the conventional diaphragm navigator such as the cardiac fat navigator and the k‐space center signal (self‐navigator) were developed to monitor heart motion directly. These navigator data can be noisy or may contain undesirable frequency components. Real‐time filtering of navigator data without delay, as opposed to the previously used retrospective frequency band filtering, is required for effective prospective navigator gating. One of the commonly used real‐time filtering techniques is the Kalman filter, which adaptively estimates motion and suppresses measurement noise by using Bayesian statistics and a motion model. The Kalman filter is investigated in this work to filter noise and distinguish cardiac and respiratory components in navigator data. Preliminary imaging data demonstrate the feasibility of real‐time Kalman filtering for prospective respiratory self‐gating in CINE cardiac MRI. Magn Reson Med 60:158–168, 2008. © 2008 Wiley‐Liss, Inc.
In vivo MRI using real‐time production of hyperpolarized 129Xe
Authors: Driehuys Bastiaan , Pollaro Jim , Cofer Gary P. 
Published: June 2008

AbstractMR imaging of hyperpolarized (HP) nuclei is challenging because they are typically delivered in a single dose of nonrenewable magnetization, from which the entire image must be derived. This problem can be overcome with HP 129Xe, which can be produced sufficiently rapidly to deliver in dilute form (1%) continuously and on‐demand. We demonstrate a real‐time in vivo delivery of HP 129Xe mixture to rats, a capability we now routinely use for setting frequency, transmitter gain, shimming, testing pulse sequences, scout imaging, and spectroscopy. Compared to images acquired using conventional fully concentrated 129Xe, real‐time 129Xe images have 26‐fold less signal, but clearly depict ventilation abnormalities. Real‐time 129Xe MRI could be useful for time‐course studies involving acute injury or response to treatment. Ultimately, real‐time 129Xe MRI could be done with more highly concentrated 129Xe, which could increase the signal‐to‐noise ratio by 100 relative to these results to enable a new class of gas imaging applications. Magn Reson Med 60:14–20, 2008. © 2008 Wiley‐Liss, Inc.
Modeling the effects of dispersion and pulsatility of blood flow in pulsed arterial spin labeling
Authors: Gallichan Daniel , Jezzard Peter 
Published: June 2008

AbstractArterial spin labeling (ASL) is a method of using MRI to image cerebral perfusion. For the measurement to be calibrated, a model is required describing the kinetics of the flow of the inverted blood from the labeling region to the imaging region. It is common to assume plug‐flow, but alternatives such as a Gaussian distribution of arrival times have also been suggested. In this study a physiologically based model for dispersion is developed and compared to existing models when fit to experimental data. The model is based on the assumption of parabolic flow in the major arteries, and also allows inclusion of cardiac pulsatility. It was found that fitting using the proposed model leads to higher perfusion estimates, with the difference becoming more pronounced in regions where the dispersion is greater. This suggests that current models may underestimate perfusion in these areas. However, fitting using the proposed model also leads to high uncertainties in parameter estimates due to non‐orthogonality of the parameters. Effects due to pulsatility are expected to be observable, but when no cardiac‐gating is used the mean curve over several cardiac cycles is predicted to closely match the curve which assumes constant flow. Magn Reson Med 60:53–63, 2008. © 2008 Wiley‐Liss, Inc.
Influence of iron chelation on R1 and R2 calibration curves in gerbil liver and heart
Authors: Wood John C. , Aguilar Michelle , Otto‐Duessel Maya , Nick Hanspeter , Nelson Marvin D. , Moats Rex 
Published: June 2008

AbstractMRI is gaining increasing importance for the noninvasive quantification of organ iron burden. Since transverse relaxation rates depend on iron distribution as well as iron concentration, physiologic and pharmacologic processes that alter iron distribution could change MRI calibration curves. This article compares the effect of three iron chelators, deferoxamine, deferiprone, and deferasirox, on R1 and R2 calibration curves according to two iron loading and chelation strategies. Thirty‐three Mongolian gerbils underwent iron loading (iron dextran 500 mg/kg/wk) for 3 weeks followed by 4 weeks of chelation. An additional 56 animals received less aggressive loading (200 mg/kg/week) for 10 weeks, followed by 12 weeks of chelation. R1 and R2 calibration curves were compared to results from 23 iron‐loaded animals that had not received chelation. Acute iron loading and chelation‐biased R1 and R2 from the unchelated reference calibration curves but chelator‐specific changes were not observed, suggesting physiologic rather than pharmacologic differences in iron distribution. Long‐term chelation deferiprone treatment increased liver R1 50% (P < 0.01), while long‐term deferasirox lowered liver R2 30.9% (P < 0.0001). The relationship between R1 and R2 and organ iron concentration may depend on the acuity of iron loading and unloading as well as the iron chelator administered. Magn Reson Med 60:82–89, 2008. © 2008 Wiley‐Liss, Inc.
Investigation of LDPE blown film instability induced by air cooling
Authors: Zhang Z. , Lafleur P.G. 
Published: June 2008

AbstractThis paper deals with the bubble instabilities induced by cooling airflow rate at different take‐up‐ratio (TUR) and blow‐up‐ratio (BUR) conditions in the film‐blowing process. Experimental methods to monitor the on‐site bubble instability included an in‐line scanning camera system to record the bubble oscillation and a manometer mounted on the die to measure the internal pressure corresponding to the radius variation. A good correlation between the bubble instability and the pressure inside the bubble has been obtained. Experimental results indicated that varying the cooling airflow rate at different TURs and BURs conditions produced significant differences in the dynamics of bubble instability. While a higher cooling air rate stabilized the bubble for a high BUR, the bubble was destabilized for a low BUR. The bubble with a high TUR sustained greater aerodynamics forces acting on the bubble surface, resulting in a broader operating range of stable operation. Finally, a numerical simulation using a RNG (renormalization group), k–ε model, and Fluent software was performed to analyze the effects of momentum and heat transfer from the cooling air to the polymer film on bubble instability. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers
A new application of biosurfactant for the preparation of polycaprolactone/layered silicate nanocomposites
Authors: Liao Hsin‐Tzu 
Published: June 2008

AbstractIn this study, by using the biosurfactant as the clay modifier, one first attempted to prepare polycaprolactone (PCL)/montmorillonite nanocomposites via a melt‐blending method. The production of biosurfactant (surfactin) and the modification of clay proceeded simultaneously by the incubation of Bacillus subtilis CWS1. The evidence for the formation of intercalated/exfoliated nanocomposites was assessed by X‐ray diffraction spectroscopy, scanning electron microscopy, and transmission electron microscopy observations. The conclusions were also supported by the result of dynamic mechanical thermal analysis, thermogravimetric analyzer, and differential scanning calorimetry. As a result, the modified clay can be well dispersed into the PCL matrix in nanoscale sizes, because the biosurfactant is partially compatible with PCL chains intercalating into clay layers. As for mechanical properties, a marked increase in tensile strength and Young's modulus can be observed when the biosurfactant‐pretreated clay was used to replace the neat clay for the preparation of nanocomposites. Based on the considerations of thermal and mechanical properties, it was also found that 10 wt% of clay content was optimal for the preparation of nanocomposite. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers
Semiempirical, squeeze flow, and intermolecular diffusion model. II. Model verification using laser microwelding
Authors: Grewell David , Benatar Avraham 
Published: June 2008

AbstractThis article reviews the application of a coupled squeeze flow and intermolecular diffusion model, which was used to predict the quality and size of microwelds in plastics. Weld widths predictions were compared with previously presented experimental results using moving heat source models and temperature fields. The motivation for this work was to develop and verify a model based on fundamental principles that could accurately predict weld size and strength for conventional plastic welding techniques as well as novel techniques such as laser microwelding. It is envisioned that the resulting model could be used to predict proper welding parameters, including laser power and travel speed, to produce welds of varying size. Although insight into weld quality can be derived from this model, it was not the goal of this work to accurately predict weld strength for laser microwelding because of the difficulty in measuring weld strength on the micron scale. However, as reported in Part 1, weld strength for impulse welds were accurately predicted. In this model it was found that variable temperature histories, rather than a single value of maximum weld temperature, allows more accurate modeling of the welding process. In this work (Part 2), microwelds as small as 11 μm in width were produced with transmission infrared welding. In addition, welds over 150‐μm wide were also generated and the model was able to predict the range of weld widths that were found experimentally. It was found that the predictions were in very good agreement with the experimental results. There was some deviation between the experimental data and the model at the extreme parameters and it is believed that this was due to the temperature‐dependent material properties as well as optical aberrations. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers
Fiber‐particle morphological transition and its effect on impact strength of PS/HDPE blends
Authors: Ramírez‐Arreola D. , Robledo‐Ortiz J. , Moscoso F. , González‐Núñez R. , Rodrigue D. 
Published: June 2008

AbstractA morphological analysis was performed to study the effect of postextrusion conditions on the properties of polystyrene (PS)/high‐density polyethylene (HDPE) blends. The results show that both draw ratio (DR) and water contact distance (X) have a definite influence on the morphology and mean failure energy (MFE) of 3, 6, and 9% PS in HDPE. In general, the MFE of the blends increases with DR up to a critical value, being function of the water contact distance, where substantial decreases are observed. It was found that deformation of the dispersed phase increases with DR, but decreases with water contact distance. However, morphological analysis of the dispersed phase shows that particle–fiber transition occurs at critical values of DR and X up to a point where fiber break‐up occurs. These morphological transitions can easily explain the impact strength behavior of the samples. Using normalized data, a master curve is proposed relating the postextrusion conditions to the MFE. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers
Ultrasound aided extrusion process for preparation of polyolefin–clay nanocomposites
Authors: Lapshin Sergey , Swain Sarat K. , Isayev Avraam I. 
Published: June 2008

AbstractA continuous ultrasound assisted process using a single screw compounding extruder with an ultrasonic attachment was developed to prepare polyolefin/clay nanocomposites. High‐density polyethylene and isotactic polypropylene were compared. The feed rate that controls the residence time of the polymer in the ultrasonic treatment zone was varied. Die pressure and power consumption were measured. Rheological properties, morphology, and mechanical properties of the untreated and ultrasonically treated nanocomposites were studied. Similarities and differences of obtained nanocomposites are discussed based on their properties and structural characteristics. The modified Halpin‐Tsai theory of composite materials has been employed in order to predict the effect of incomplete exfoliation of clay platelets on the Young's modulus of the nanocomposites. A good agreement between experimental and theoretical data has been observed when reduction of the reinforcement efficiency of clay had been incorporated through the reduced aspect ratio of elementary clay platelets. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers
Chromophore concentration effect on holographic grating formation efficiency in novel azobenzene‐functionalized polymers
Authors: Schab‐Balcerzak Ewa , Sobolewska Anna , Miniewicz Andrzej , Jurusik Jan 
Published: June 2008

AbstractOptically active photochromic poly(amideimide)s containing azobenzene side groups in the repeating unit were prepared. The polymers were designed and synthesized specifically for this work in order to evaluate chromophore concentration effect on holographic grating recording. The poly(amideimide)s with mono‐ and bis‐azobenzene moieties were obtained via direct high temperature polycondensation and compared with respect to their ability of diffraction grating formation due to the light‐induced optical anisotropy effects. Holographic gratings were fabricated in polymer films upon exposure to an interference pattern of two polarized Ar+ laser beams at 514.5 nm wavelength. Different geometries of laser beams polarization were applied. It should be emphasized that although the azobenzene moieties are rigidly connected to the polymers backbone, some of polymers exhibited the unusually high light diffraction efficiency of around 40%. The created surface relief gratings (SRGs) were successfully observed using the atomic force microscopy (AFM). AFM images show regularly defined and aligned grating structures. It should be stressed that the SRGs with maximum of relief height up to 260 nm in polyimide derivatives with side azobenzene group were observed for the first time. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers