bluuebunny/crossref_metadata_2025_split huggingface dataset:
Defining a local arterial input function for perfusion MRI using independent component analysis
Authors: Calamante Fernando , Mørup Morten , Hansen Lars Kai 
Published: September 2004

AbstractQuantification of cerebral blood flow (CBF) using dynamic‐susceptibility contrast MRI relies on the deconvolution of the arterial input function (AIF), which is commonly estimated from the signal changes in a major artery. However, it has been shown that the presence of bolus delay/dispersion between the artery and the tissue of interest can be a significant source of error. These effects could be minimized if a local AIF were used, although the measurement of a local AIF can be problematic. This work describes a new methodology to define a local AIF using independent component analysis (ICA). The methodology was tested on data from patients with various cerebrovascular abnormalities and compared to the conventional approach of using a global AIF. The new methodology produced higher CBF and shorter mean transit time values (compared to the global AIF case) in areas with distorted AIFs, suggesting that the effects of delay/dispersion are minimized. The minimization of these effects using the calculated local AIF should lead to a more accurate quantification of CBF, which can have important implications for diagnosis and management of patients with cerebral ischemia. Magn Reson Med 52:789–797, 2004. © 2004 Wiley‐Liss, Inc.
Simple, low‐cost multipurpose RF coil for MR microscopy at 9.4 T
Authors: Bilgen Mehmet 
Published: September 2004

AbstractAn inductively coupled RF coil is introduced for high‐resolution MR studies at 9.4 T. The coil offers the flexibility of use as an implantable coil for local imaging inside the body or as a surface coil for imaging below complex surfaces. Successful operation of this coil at strong magnetic field requires special design considerations. In this note, implementation issues of the coil are discussed in detail and practical solutions to overcome some of these difficulties are offered. Imaging performance of the coil and its versatility are demonstrated with images acquired from rat spinal cord when the coil is implanted, and mouse spine and brain when the coil is placed on the surface. Magn Reson Med 52:937–940, 2004. © 2004 Wiley‐Liss, Inc.
Different physiological MRI noise between cortical layers
Authors: Pelled Galit , Goelman Gadi 
Published: September 2004

AbstractSignificantly higher temporal fluctuations of the blood oxygenation level‐dependent (BOLD) signal in the living rat group compared to that in the dead rat group were observed in the cortex, suggesting the existence of physiological information in the signal fluctuations. A similar analysis shows significantly different fluctuations between visual cortical layers. The highest fluctuations were observed in layers 4 and 5 and the lowest in layer 1. Given the consistency with published electrophysiology studies anticipating high spontaneous activity in the deeper layers (particularly layer 4), and low activity in superficial layers, we hypothesize that the BOLD signal temporal fluctuations may reflect cortical neuronal activity. Temporal fluctuations in ultrahigh spatial resolution data of the rat brain were measured in two ways. In the first, analyses were performed according to known layer widths, and in the second equal lines of 117 μ along the cortex were selected. The second approach yielded temporal fluctuations along the cortex that resemble known neuronal density distributions including the intralayer structure, particularly within layer 5. Magn Reson Med 52:913–916, 2004. © 2004 Wiley‐Liss, Inc.
SSFP‐based MR thermometry
Authors: Paliwal Vaishali , El‐Sharkawy AbdEl‐Monem , Du Xiangying , Yang Xiaoming , Atalar Ergin 
Published: September 2004

AbstractOf the various techniques employed to quantify temperature changes by MR, proton resonance frequency (PRF) shift‐based phase‐difference imaging (PDI) is the most accurate and widely used. However, PDI is associated with various artifacts. Motivated by these limitations, we developed a new method to monitor temperature changes by MRI using the balanced steady‐state free precession (balanced‐SSFP) pulse sequence. Magnitude images obtained with the SSFP pulse sequence were used to find the PRF shift, which is proportional to temperature change. Spatiotemporal temperature maps were successfully reconstructed with this technique in gel phantom experiments and a rabbit model. The results show that the balanced‐SSFP‐based method is a promising new technique for monitoring temperature. Magn Reson Med 52:704–708, 2004. © 2004 Wiley‐Liss, Inc.
Displacement‐encoded cardiac MRI using cosine and sine modulation to eliminate (CANSEL) artifact‐generating echoes
Authors: Epstein Frederick H. , Gilson Wesley D. 
Published: September 2004

AbstractDisplacement‐encoded imaging with stimulated echoes (DENSE) and harmonic phase imaging (HARP) employ 1‐1 spatial modulation of magnetization to cosine modulate the longitudinal magnetization as a function of position at end diastole. Later in the cardiac cycle they sample the cosine‐modulated signal and compute myocardial strain from the signal phase. The sampled signal generally includes three distinct echoes: 1) a displacement‐encoded stimulated echo, 2) the complex conjugate of the displacement‐encoded echo, and 3) an echo arising from T1 relaxation. If the T1‐relaxation and complex conjugate echoes are suppressed, then a phase image representing just the displacement‐encoded echo can be reconstructed. In the present study, the use of cosine and sine modulation to eliminate (CANSEL) the T1‐relaxation and complex conjugate echoes was investigated. With the use of CANSEL, it was demonstrated that DENSE accurately measures through‐plane as well as in‐plane components of tissue motion. Also, DENSE with CANSEL artifact suppression can provide increased signal‐to‐noise ratio (SNR) secondary to reduced intravoxel dephasing by using relatively low displacement‐encoding frequencies. For applications that employ DENSE imaging with multiple acquisitions, the CANSEL technique can suppress artifact‐generating echoes without placing constraints on the displacement‐encoding frequency and direction. Magn Reson Med 52:774–781, 2004. © 2004 Wiley‐Liss, Inc.
Optimal design of k‐space trajectories using a multi‐objective genetic algorithm
Authors: Dale Brian M. , Lewin Jonathan S. , Duerk Jeffrey L. 
Published: September 2004

AbstractSpiral, radial, and other nonrectilinear k‐space trajectories are an area of active research in MRI due largely to their typically rapid acquisition times and benign artifact patterns. Trajectory design has commonly proceeded from a description of a simple shape to an investigation of its properties, because there is no general theory for the derivation of new trajectories with specific properties. Here such a generalized methodology is described. Specifically, a multi‐objective genetic algorithm (GA) is used to design trajectories with beneficial flow and off‐resonance properties. The algorithm converges to a well‐defined optimal set with standard spiral trajectories on the rapid but low‐quality end, and a new class of trajectories on the slower but high‐quality end. The new trajectories all begin with nonzero gradient amplitude at the k‐space origin, and curve gently outward relative to standard spirals. Improvements predicted in simulated imaging experiments were found to correlate well with improvements in actual experimental measures of image quality. The impact of deviations from the desired k‐space trajectory is described, as is the impact of using different phantoms. Magn Reson Med 52:831–841, 2004. © 2004 Wiley‐Liss, Inc.
Improving the spatial specificity of canonical correlation analysis in fMRI
Authors: Nandy Rajesh , Cordes Dietmar 
Published: September 2004

AbstractThe contrast‐to‐noise ratio (CNR) is often very low in fMRI data, and standard univariate methods suffer from a loss of sensitivity in the context of noise. The increased power of a multivariate statistical analysis method known as canonical correlation analysis (CCA) in fMRI studies with low CNR was established previously. However, CCA in its conventional form has weak spatial specificity. In this work we propose a new assignment scheme to rectify this problem. It is shown that the new method has improved spatial specificity as well as sensitivity compared to conventional CCA for detecting activation patterns in fMRI. Magn Reson Med 52:947–952, 2004. © 2004 Wiley‐Liss, Inc.
Dynamic MRI with projection reconstruction and KWIC processing for simultaneous high spatial and temporal resolution
Authors: Song Hee Kwon , Dougherty Lawrence 
Published: September 2004

AbstractA method for dynamic imaging in MRI is presented that enables the acquisition of a series of images with both high temporal and high spatial resolution. The technique, which is based on the projection reconstruction (PR) imaging scheme, utilizes distinct data acquisition and reconstruction strategies to achieve this simultaneous capability. First, during acquisition, data are collected in multiple undersampled passes, with the view angles interleaved in such a way that those of subsequent passes bisect the views of earlier ones. During reconstruction, these views are weighted according to a previously described k‐space weighted image contrast (KWIC) technique that enables the manipulation of image contrast by selective filtering. Unlike conventional undersampled PR methods, the proposed dynamic KWIC technique does not suffer from low image SNR or image degradation due to streaking artifacts. The effectiveness of dynamic KWIC is demonstrated in both simulations and in vivo, high‐resolution, contrast‐enhanced imaging of breast lesions. Magn Reson Med 52:815–824, 2004. © 2004 Wiley‐Liss, Inc.
Observation of nonlinear shear wave propagation using magnetic resonance elastography
Authors: Sack Ingolf , Mcgowan Christopher K. , Samani Abbas , Luginbuhl Chris , Oakden Wendy , Plewes Donald B. 
Published: September 2004

AbstractMR elastography (MRE) is an MRI modality that is increasingly being used to image tissue elasticity throughout the body. One MRE technique that has received a great deal of attention is based on visualizing shear waves, which reveal stiffness by virtue of their local wavelength. However, the shape of propagating shear waves can also provide valuable information about the nonlinear stress–strain behavior of tissue. Here an experiment is proposed that allows the observation of nonlinear wave propagation based on spatial‐temporal phase contrast images. A theoretical description of the wave propagation was developed that reflects typical MRE excitation, which involves excitation modes both parallel and perpendicular toB0. Based on this model, it is shown that both odd and even higher harmonics are produced with their amplitudes dependent on the details of the actuator, imaging geometry, and the nonlinear tissue properties. With appropriate motion encoding, harmonic vibrations arising from nonlinear tissue response can be detected. The effect is demonstrated on an agarose gel phantom using a sinusoidal shear vibration of 150 Hz, and clearly shows the presence of harmonics at 600 and 750 Hz. Using an estimate of the strain energy of the phantom, we were able to determine the nonlinear tissue properties. Magn Reson Med 52:842–850, 2004. © 2004 Wiley‐Liss, Inc.
Single‐acquisition sequence for the measurement of oxygen partial pressure by hyperpolarized gas MRI
Authors: Fischer M.C. , Spector Z.Z. , Ishii M. , Yu J. , Emami K. , Itkin M. , Rizi R. 
Published: September 2004

AbstractMagnetic resonance imaging (MRI) with hyperpolarized 3‐helium gas (HP 3He) offers the possibility of studying functional lung parameters such as the alveolar oxygen concentration and oxygen depletion rate. Until now, a double‐acquisition technique has been utilized to extract these parameters. A complicated single‐acquisition technique was previously developed to avoid the necessity of performing two identical breathing maneuvers. The results obtained with this technique were significantly less accurate than the results obtained with the double‐acquisition method. In this work, a novel, easily implemented single‐acquisition sequence is presented that provides results comparable to those obtained with the established double‐acquisition method. This method is demonstrated in a phantom and a pig model on a 1.5 T scanner using a 2D fast low‐angle shot (FLASH) gradient‐echo sequence. Numerical simulations of the time evolution of the oxygen concentration were performed. Simulation results are presented to support the experimental data. Various parameter regimes were experimentally and numerically investigated. Magn Reson Med 52:766–773, 2004. © 2004 Wiley‐Liss, Inc.
NMR analysis of neutrophil activation in sputum samples from patients with cystic fibrosis
Authors: Saude Erik J. , Lacy Paige , Musat‐Marcu Sorin , Mayes Damon C. , Bagu John , Man S.F. Paul , Sykes Brian D. , Moqbel Redwan 
Published: September 2004

AbstractDisorders of the respiratory system, such as cystic fibrosis (CF), involve the infiltration and activation of airway inflammatory cells, including neutrophils. This leads to the secretion of peroxidases, which react further with substrates in solution to produce oxidative metabolites, such as 3‐chlorotyrosine. Elevated levels of modified tyrosine residues in the airways of patients with CF may be detectable by nuclear magnetic resonance (NMR) in correlation with inflammatory cell influx. In this study, high‐resolution (500 MHz) 1H NMR was used to analyze the production of modified tyrosine residues resulting from in vitro stimulation of peripheral blood eosinophils and neutrophils, as well as in sputum samples from control subjects and patients with CF. Following in vitro stimulation, purified peripheral blood neutrophils generated 3‐chlorotyrosine, while eosinophils produced predominantly 3‐bromotyrosine and 3,5‐dibromotyrosine. Chlorinated and brominated tyrosine residues were detected in sputum samples from patients with CF (N = 7), but were not detected in the control group (N = 9). Neutrophil counts in CF sputum correlated strongly with the presence of 3‐chlorotyrosine (r2 = 0.869). Our findings indicate that neutrophil and eosinophil activation in CF is detectable by NMR. NMR may be a useful tool for the detection of biological markers of inflammatory processes in patient airways. Magn Reson Med 52:807–814, 2004. © 2004 Wiley‐Liss, Inc.
Spatial chaos of 3‐D elastica with the Kirchhoff gyrostat analogy using Melnikov integrals
Authors: Leung A. Y. T. , Kuang J. L. 
Published: September 2004

AbstractThe Kirchhoff kinetic analogy, from which the similarity between the governing equations for the static spatial equilibrium of a 3‐D elastica and those for the temporal dynamics of a rigid body is constituted, is revisited. The Melnikov integrals for detecting chaos cannot be easily formed for an elastica. We shall modify the previous procedure of using the Melnikov integrals for detecting temporal chaos for a gyrostat to solve the spatial chaos problem of an elastica. One way to find the disturbed Hamiltonian equations of the equilibrium equations of the elastica are by means of Deprit's variables. Using the Melnikov integrals, the spatially chaotic deformation patterns can be resulted from the homoclinic transversal intersections of the stable and unstable manifolds at a saddle point in the Poincare map when the elastica is disturbed by constant stress‐resultants. The Melnikov integrals are integrated for detecting homoclinic intersections. The equations governing the evolution of the stress‐couples and the stress‐resultants are numerically integrated using the fourth Runge–Kutta algorithms to crosscheck the analytical results. The phase portraits of the Poincare sections are created on a number of hyper‐planes to demonstrate the chaotic patterns of the stationary spatial deformations along the centreline of the elastica under weightless conditions. The bounded, non‐periodic solutions to the equilibrium of the elastica clearly show the existence of spatially chaotic deformation patterns. The findings in this paper are useful in many structures in which the elastica are important. Examples are the mathematical modelling of the DNA super‐coiling, submarine cables and the design of the tethered satellites. Copyright © 2004 John Wiley & Sons, Ltd.
Generating signals of drug‐adverse effects from prescription databases and application to the risk of arrhythmia associated with antibacterials
Authors: Corrao Giovanni , Botteri Edoardo , Bagnardi Vincenzo , Zambon Antonella , Carobbio Alessandra , Falcone Chiara , Leoni Olivia 
Published: September 2004

AbstractBackgroundAlthough it is well known that a variety of antibacterials may incidentally cause malignant arrhythmia, the list of drugs causing arrhythmia and the impact of these adverse effects are still uncertain. We investigated on this topic by using a large prescription database with different observational designs.MethodsPrescription data on all incident users of several antibacterial and antiarrhythmic drugs over the period July 1997 through December 1999 were retrieved from the Drug Prescription Database (DPD) of the Italian Province of Varese. The association between the use of antibacterial and antiarrhythmic drugs was investigated by applying prescription sequence symmetry, cohort and nested case‐control designs.ResultsLower proarrhythmic effects were on an average obtained from prescription sequence symmetry approach with respect to both cohort and nested case‐control. Evidence of association between exposure to drugs (erythromycin and ciprofloxacin) and the risk of arrhythmia was consistently found by the three approaches. No other signals were generated from the prescription sequence symmetry analysis. Two drugs (clarithromycin and levofloxacin) showed patterns compatible with an arrhythmic effect according to both cohort and nested case‐control designs.ConclusionsPrescription databases are useful tools to explore drug safety through both conventional and emerging observational designs. In spite of its appealing features, prescription sequence symmetry design shows lower sensitivity with respect to conventional designs. Evidence about the association between the use of certain macrolides and fluoroquinolones and the onset of arrhythmia is confirmed by this study. Copyright © 2004 John Wiley & Sons, Ltd.
Reaction‐induced phase separation in epoxy/polysulfone/poly(ether imide) systems. I. Phase diagrams
Authors: Giannotti M. I. , Foresti M. L. , Mondragon I. , Galante M. J. , Oyanguren P. A. 
Published: September 2004

AbstractEpoxy–aromatic diamine formulations are simultaneously modified with two immiscible thermoplastics (TPs), poly(ether imide) (PEI) and polysulfone (PSF). The epoxy monomer is based on diglycidyl ether of bisphenol A and the aromatic diamines (ADs) are either 4,4′‐diaminodiphenylsulfone or 4,4′‐methylenebis(3‐chloro 2,6‐diethylaniline). The influence of the TPs on the epoxy–amine kinetics is investigated. It is found that PSF can act as a catalyst. The presence of the TP provokes an increase of the gel times. Cloud‐point curves (temperature vs. composition) are shown for epoxy/PSF/PEI and epoxy/PSF/PEI/AD initial mixtures. Phase separation conversions are reported for the reactive mixtures with various TP contents and PSF/PEI proportions. On the basis of phase separation and gelation curves, conversion–composition phase diagrams at constant temperature are generated for both systems. These diagrams can be used to design particular cure cycles to generate different morphologies during the phase separation process, which is discussed in the second part of this series. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3953–3963, 2004
Dielectric study of the phase diagram of the poly(γ‐benzyl‐L‐glutamate)/dimethylformamide system
Authors: Dereszewska A. , Alegria A. , Olayo R. 
Published: September 2004

AbstractThe phase diagram for solutions of poly(γ‐benzyl‐L‐glutamate) in dimethylformamide has been investigated over the entire composition and temperature ranges with dielectric spectroscopy. The dielectric response in this system is dominated by ionic mobility, and phase transitions have been detected as changes in the ionic conductivity. The phase boundaries, determined by dielectric spectroscopy, are consistent with earlier published results obtained by a combination of optical microscopy observations and nuclear magnetic resonance and differential scanning calorimetry studies. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3943–3952, 2004
A Moving Average Control Chart for Monitoring the Fraction Non‐conforming
Authors: Khoo Michael B. C. 
Published: September 2004

AbstractThe p chart is often used to monitor the fraction of non‐conforming products. However, the p chart is slow in detecting sustaining shifts of small magnitude in the level of fraction non‐conforming. This paper discusses a more efficient alternative to the standard p chart approach, i.e. the construction of a moving average control chart for fraction non‐conforming, p. Approximations by means of mathematical calculations and the corresponding simulation results for the average run length profiles show that the performance of the new approach is superior to that of the standard approach. The new approach is easy to implement and hence might be attractive and useful to practitioners. Examples are also given to show how the proposed procedure is put to work in real situations. Copyright © 2004 John Wiley & Sons, Ltd.
The ability of the Gaussian‐2, Gaussian‐3, Complete Basis Set–QB3, and Complete Basis Set–APNO model chemistries to model the geometries of small water clusters
Authors: Dunn Meghan E. , Pokon Emma K. , Shields George C. 
Published: September 2004

AbstractThe Gaussian‐2, Gaussian‐3, Complete Basis Set‐QB3, and Complete Basis Set‐APNO methods have been used to calculate geometries of neutral clusters of water, (H2O)n, where n = 2–6. The structures are in excellent agreement with those determined from experiment and those predicted from previous high‐level calculations. These methods also provide excellent thermochemical predictions for water clusters, and thus can be used with confidence in evaluating the structures and thermochemistry of water clusters. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004