bluuebunny/crossref_metadata_2025_split huggingface dataset:
Time‐resolved MR angiography with limited projections
Authors: Huang Yuexi , Wright Graham A. 
Published: July 2007

AbstractA method for reconstruction of time‐resolved MRI called highly‐constrained backprojection (HYPR) has been developed. To evaluate the HYPR reconstruction in relation to data sparsity and temporal dynamics, computer simulations were performed, investigating signal modulations under different situations that reflect dynamic contrast‐enhanced MR angiography (MRA). In vivo studies were also performed with gadolinium diethylenetriamine pentaacetic acid (Gd‐DTPA) for abdominal MRA in a canine model to demonstrate the application of HYPR for three‐dimensional (3D) time‐resolved MRA. When contrast dynamics vary over space, large vessels (e.g., veins) tend to introduce signal interference to small vessels (e.g., arteries) in HYPR, particularly when the vessels are in close proximity. The enhancement of background tissue signals may also alter the arterial and venous temporal profiles in HYPR. However, the artifacts are manifest as intensity modulation rather than structural interference, and therefore have little impact on structural diagnosis. Increasing the number of projections per time point increases temporal blur while reducing corruption of temporal behavior from adjacent tissues. Uniformly interleaved acquisition order, such as the bit‐reversed order, is important to reduce artifacts. With high signal‐to‐noise ratio (SNR) and limited artifacts, HYPR reconstruction has potential to greatly improve time‐resolved MRA in clinical practice. Magn Reson Med 58:316–325, 2007. © 2007 Wiley‐Liss, Inc.
T1 relaxation in in vivo mouse brain at ultra‐high field
Authors: van de Ven Rob C.G. , Hogers Bianca , van den Maagdenberg Arn M.J.M. , de Groot Huub J.M. , Ferrari Michel D. , Frants Rune R. , Poelmann Robert E. , van der Weerd Louise , Kiihne Suzanne R. 
Published: July 2007

AbstractAccurate knowledge of relaxation times is imperative for adjustment of MRI parameters to obtain optimal signal‐to‐noise ratio (SNR) and contrast. As small animal MRI studies are extended to increasingly higher magnetic fields, these parameters must be assessed anew. The goal of this study was to obtain accurate spin‐lattice (T1) relaxation times for the normal mouse brain at field strengths of 9.4 and 17.6 T. T1 relaxation times were determined for cortex, corpus callosum, caudate putamen, hippocampus, periaqueductal gray, lateral ventricle, and cerebellum and varied from 1651 ± 28 to 2449 ± 150 ms at 9.4 T and 1824 ± 101 to 2772 ± 235 ms at 17.6 T. A field strength–dependent increase of T1 relaxation times is shown. The SNR increase at 17.6 T is in good agreement with the expected SNR increase for a sample‐dominated noise regime. Magn Reson Med 58:390–395, 2007. © 2007 Wiley‐Liss, Inc.
A noniterative method to design large‐tip‐angle multidimensional spatially‐selective radio frequency pulses for parallel transmission
Authors: Xu Dan , King Kevin F. , Zhu Yudong , McKinnon Graeme C. , Liang Zhi‐Pei 
Published: July 2007

AbstractRecently, theoretical and experimental work has shown that parallel transmission of RF pulses can be used to shorten the duration of multidimensional spatially‐selective pulses and compensate for B1 field inhomogeneity. However, all the existing noniterative methods can design only excitation pulses for parallel transmission with a small flip angle (e.g., 30°, or at most 90°) and cannot design large‐tip‐angle inversion/refocusing pulses, because these methods are based on the small‐tip‐angle (STA) approximation of the Bloch equation. In this work, a method to design large‐tip‐angle multidimensional spatially‐selective pulses for parallel transmission is proposed, based on an extension of the single‐channel linear‐class large‐tip‐angle (LCLTA) theory. Design examples of 2D refocusing and inversion parallel transmit pulses and magnetization profiles from Bloch equation simulations demonstrate the strength of the proposed method. A 2D spin‐echo parallel transmission experiment on a slab phantom using a 180° refocusing pulse with an eight‐channel transmit‐only array further validates the effectiveness of the proposed method. Magn Reson Med 58:326–334, 2007. © 2007 Wiley‐Liss, Inc.
Noninvasive diffusion tensor imaging of evolving white matter pathology in a mouse model of acute spinal cord injury
Authors: Kim Joong Hee , Loy David N. , Liang Hsiao‐Fang , Trinkaus Kathryn , Schmidt Robert E. , Song Sheng‐Kwei 
Published: July 2007

AbstractWe examined in vivo measurements of directional diffusivity derived from diffusion tensor imaging (DTI) to study the evolution of ventrolateral white matter (VWM) changes following contusive spinal cord injury (SCI) in C57BL/6 mice at 1, 3, 7, and 14 days postinjury. Relative anisotropy maps provided excellent gray matter (GM)/white matter (WM) contrast for characterization of evolving WM injury at all time points. Longitudinal DTI measurements clearly demonstrated rostral‐caudal injury asymmetry. Axial diffusivity provided a sensitive, noninvasive measure of axonal integrity within the injury epicenter and at remote levels. Quantitative measurements of axial and radial diffusivities in VWM showed a trend of acute primary axonal injury followed by delayed, subacute myelin damage at the impact site, with good histological correlation. Magn Reson Med 58:253–260, 2007. © 2007 Wiley‐Liss, Inc.
What levels of precision are achievable for quantification of perfusion and capillary permeability surface area product using ASL?
Authors: Carr John P. , Buckley David L. , Tessier Jean , Parker Geoff J.M. 
Published: July 2007

AbstractWe examine the use of arterial spin labeling (ASL) in normal brains of rats and humans to measure perfusion (F) and capillary permeability surface area product (PS) using a previously described two‐compartment model. We investigate the experimental limits on F and PS quantification using simulations and experimental verification in rat brain at 9.4T. A sensitivity analysis on the two‐compartment model is presented to estimate optimal experimental inversion times (TIs) for F and PS quantification and indicate how sensitive the model would be to changes in F and PS. We present the expected error on flow‐sensitive alternating inversion recovery (FAIR)‐based F and PS measurements and quantify the precision with which these parameters could be estimated at various signal‐to‐noise ratios (SNRs). Perfusion was measured in four rat brains using FAIR ASL, and we conclude that perfusion could be quantified with an acceptable level of precision using this technique. However, we found that to measure PS with even a 100% coefficient of variation (CV) would require an SNR increase of approximately 2 orders of magnitude over our acquired data. We conclude that with current MR capabilities and with the experimental approach used in this study, acceptable levels of precision in the measurement of PS are not possible. Magn Reson Med 58:281–289, 2007. © 2007 Wiley‐Liss, Inc.
Functional imaging with FENSI: Flow‐enhanced signal intensity
Authors: Sutton Bradley P. , Ouyang Cheng , Ching Bryce L. , Ciobanu Luisa 
Published: July 2007

AbstractFlow measurement methods for functional MRI (fMRI) are desirable as they are more closely tied to neuronal activity than the commonly used blood oxygenation techniques. In this work we introduce a flow‐based functional imaging method. The method, called flow enhancement of signal intensity (FENSI), is an extension of the diffusion enhancement of signal and resolution (DESIRE) method from MR microscopy. The FENSI method offers a localized flow‐weighted signal across a very thin slice (0.4 mm in this study) that provides a signal enhancement that is dependent on the velocity and direction of the flow. The FENSI method was implemented on a human 3 T system and applied to a blocked visual cognitive task. Activation maps showed good localization and the measured signal changes of around 10% were in good agreement with the predicted enhancements. Magn Reson Med 58:396–401, 2007. © 2007 Wiley‐Liss, Inc.
Optimization of fast spiral chemical shift imaging using least squares reconstruction: Application for hyperpolarized 13C metabolic imaging
Authors: Levin Y.S. , Mayer D. , Yen Y.‐F. , Hurd R.E. , Spielman D.M. 
Published: July 2007

AbstractA least‐squares–based optimization and reconstruction algorithm has been developed for rapid metabolic imaging in the context of hyperpolarized 13C. The algorithm uses a priori knowledge of resonance frequencies, J‐coupling constants, and T2* values to enable acquisition of high‐quality metabolic images with imaging times of approximately 100 ms for an 8‐cm field of view (FOV) and 0.5 cm isotropic resolution. A root‐mean‐square error (rMSE) analysis is introduced to optimize metabolic image quality by appropriate choice of pulse sequence parameters, echo times, and signal model. By performing the reconstruction in k‐space, the algorithm also allows the inclusion of the effect of chemical shift evolution during the readout period. Single‐interleaf multiecho spiral chemical shift imaging (spCSI) is analyzed in detail as an illustrative example for the use of the new reconstruction and optimization algorithm. Simulation of the in vivo spectrum following the bolus injection of hyperpolarized 13C1 pyruvate shows that single‐interleaf spiral spectroscopic imaging can achieve image quality in 100 ms, comparable to the performance of a 13‐s phase‐encoded chemical shift imaging (FIDCSI) experiment. Single‐interleaf spCSI was also tested at a 3‐T MR scanner using a phantom containing approximately 0.5‐M solutions of alanine, lactate, and a pyruvate‐pyruvate hydrate C1‐C2 ester at thermal equilibrium polarization, all enriched to 99% 13C in the C1 carbonyl positions. Upon reconstruction using the k‐space–based least‐squares technique, metabolite ratios obtained using the spCSI method were comparable to those obtained using a reference FIDCSI acquisition. Magn Reson Med 58:245–252, 2007. © 2007 Wiley‐Liss, Inc.
MRI estimation of contrast agent concentration in tissue using a neural network approach
Authors: Bagher‐Ebadian Hassan , Nagaraja Tavarekere N. , Paudyal Ramesh , Whitton Polly , Panda Swayamprava , Fenstermacher Joseph D. , Ewing James R. 
Published: July 2007

AbstractUsing an MRI T1 by multiple readout pulses (TOMROP) image set, an adaptive neural network (ANN) was trained to directly estimate the concentration of a contrast agent (CA), gadolinium‐bovine serum albumin (Gd‐BSA), in tissue. In nine rats implanted with a 9L cerebral tumor, MRI acquisition of TOMROP inversion‐recovery data was followed by quantitative autoradiography (QAR) using radioiodinated serum albumin (RISA). QAR autoradiograms were used as a training set for the ANN. Precontrast and 25 min postcontrast TOMROP image sets were shown to the ANN in the form of a physical feature set related to 24 inversion‐recovery images; QAR autoradiograms at 30 min after injection of RISA were taken as the training standard for the network. After training and optimization, the ANN produced a map of Gd‐BSA concentration [g‐moles/liter]. The prediction by the ANN of CA concentration at 25 min after injection was well correlated (r = 0.82, P < 0.0001) with the corresponding autoradiogram's measure of CA concentration. Magn Reson Med 58:290–297, 2007. © 2007 Wiley‐Liss, Inc.
Response of choline metabolites to docetaxel therapy is quantified in vivo by localized 31P MRS of human breast cancer xenografts and in vitro by high‐resolution 31P NMR spectroscopy of cell extracts
Authors: Morse David L. , Raghunand Natarajan , Sadarangani Pooja , Murthi Shiva , Job Constantin , Day Sam , Howison Christine , Gillies Robert J. 
Published: July 2007

AbstractCholine‐containing compounds (CCCs) are elevated in breast cancer, and detected in vivo by the 1H MRS total choline (tCho) resonance (3.25 ppm) and the 31P MRS phosphomonoester (PME) resonance (3.8 ppm). Both the tCho and PME resonances decrease early after initiation of successful therapy. The single major component of these composite resonances, phosphocholine (PCho), also responds to therapy by decreasing. The ability to resolve and quantify PCho in vivo would thus increase the sensitivity of this biomarker for early detection of therapeutic response.Herein, the in vivo resolution and quantification of PCho is reported in human mouse xenograft tumors of the human breast cancer cell lines MCF‐7 and MDA‐mb‐231. Significant decreases in tumor PCho are observed within 2 to 4 d posttreatment with the antimicrotubule drug, docetaxel. To determine whether these decreases are a general tumor response or an intracellular metabolic response, high‐resolution NMR spectroscopy was performed on extracts of cells treated with docetaxel. Significant decreases in intracellular PCho and increases in glycerophosphocholine (GPC) were observed. These decreases are coincident with other tumor and cellular responses such as tumor growth delay (TGD), cell‐cycle arrest, and modes of cell death such as mitotic catastrophe, necrosis, and apoptosis, with mitotic catastrophe predominating. Magn Reson Med 58:270–280, 2007. © 2007 Wiley‐Liss, Inc.
On the identifiability of pharmacokinetic parameters in dynamic contrast‐enhanced imaging
Authors: Lopata Richard G.P. , Backes Walter H. , van den Bosch Paul P.J. , van Riel Natal A.W. 
Published: July 2007

AbstractThe so‐called “Kety model” is a two‐compartment pharmacokinetic model describing tumor perfusion kinetics. Its parameters, the transendothelial transfer constant (Ktrans), extravascular extracellular volume fraction (υe), and microvascular plasma volume fraction (υp), can be estimated with dynamic contrast‐enhanced magnetic resonance imaging (DCE‐MRI). However, the results obtained by current methods show large variation in predictability and reliability. Here, the aim was to examine which experimental conditions have to be fulfilled to avoid large uncertainties and mutual dependencies of the parameters. Using frequency response analysis and simulation, the identifiability of the model was examined. The requirements and influence of contrast enhancement measurements, such as temporal resolution, signal to noise ratio, and contrast injection rate, on the accuracy of the parameters were analyzed. Tissue response characteristics revealed a low‐frequency system with a cutoff frequency equal to Ktrans/υe, which confines the required temporal resolution. For malignant tissue with hyperpermeable vasculature (high Ktrans) a higher sampling frequency is required to accurately estimate Ktrans than for normal tissue. Too low sampling rates or too low injection rates resulted in inaccurate Ktrans values and hereby unreliable classification of malignant tissue. Magn Reson Med 58:425–429, 2007. © 2007 Wiley‐Liss, Inc.
Synemin expression in brain
Authors: Mizuno Yuji , Guyon Jeffrey R. , Okamoto Koichi , Kunkel Louis M. 
Published: July 2007

Abstractβ‐Synemin has been identified as an α‐dystrobrevin–interacting protein in human muscle, although at least two synemin transcripts are expressed in brain. To understand synemin's function in neural tissue, in situ and immunohistochemical analyses were performed to identify where α‐ and β‐synemin are expressed in the brain of C57BL/6 and mdx (dystrophin null) mice. This analysis shows that the α‐ and β‐synemin transcripts and their encoded proteins colocalize in neurons, especially in the midbrain and pons. Since α‐dystrobrevin‐1 and synemin do not colocalize in brain as in muscle, this suggests that another member of the dystrophin‐associated protein complex might interact with synemin in brain. In support of this, synemin mRNA expression was decreased in mdx mice, suggesting that synemin transcription is linked to dystrophin expression. Our findings show where synemin is expressed in brain and allow one to speculate with regard to its function in neural tissue. Muscle Nerve, 2007
Multiple measures of axonal excitability in peripheral sensory nerves: An in vivo rat model
Authors: George Annette , Bostock Hugh 
Published: July 2007

AbstractExcitability measurements on human motor and sensory nerves have provided new insights into axonal membrane changes in peripheral nerve disorders. The aim of this study was to establish an in vivo rat preparation suitable for threshold tracking of sensory nerve action potentials (SNAPs) to model clinical sensory nerve excitability studies. In Sprague–Dawley rats anesthetized with ketamine and xylazine, current stimuli were applied to the base of the tail and SNAPs recorded from distal needle electrodes. Multiple excitability data were obtained as previously described for human nerves and compared to recordings from the motor tail axons and to sensory recordings from human median and ulnar nerves. The pattern of excitability changes in rats was broadly similar to that in humans, although some parameters differed significantly. Individual recordings were stable for at least 3 h. These data show that the rat tail enables excitability properties of sensory as well as motor axons to be studied experimentally, e.g., in models of nerve disease and during pharmacological interventions. Muscle Nerve, 2007
Comparative efficacy of repetitive nerve stimulation, exercise, and cold in differentiating myotonic disorders
Authors: Michel Patrik , Sternberg Damien , Jeannet Pierre‐Yves , Dunand Murielle , Thonney Francine , Kress Wolfram , Fontaine Bertrand , Fournier Emmanuel , Kuntzer Thierry 
Published: July 2007

AbstractThe decremental response of the compound muscle action potential (CMAP) to provocative tests is not characterized in genetically verified myotonic disorders. We therefore studied the relationship between decremental responses and mutation type in 10 patients with recessive myotonia congenita (rMC), two with paramyotonia congenita (PMC), nine with myotonic dystrophy type 1 (DM1), four with DM2, and 14 healthy people. CMAPs were measured at rest, just after a short exercise test (SET), and during short, 5‐ and 10‐HZ, repetitive nerve stimulation (RNS) trains at 32°C and at 20°C. The degree of decrement was not related to the severity of clinical myotonia. Controls and PMC patients had similar responses when warm, but with cooling PMC patients had a persistent decrement of CMAPs. In the rMC patients the decremental responses were related to the type of mutation of the CLCN1 gene, as a decrement was encountered in the T268M, R894X, IVS17+1 G>T, K248X, and 2149 del G, but not with the IVS1+3 A>T, F167L, or dominant A313T mutations. In DM1 patients there was no relationship between decrement and CTG repeats. The degree of partial inexcitability in myotonic muscle membrane therefore depends on the mutation type rather than degree of clinical myotonia. RNS at 10 HZ is more sensitive than SET for demonstrating abnormalities in rMC patients when warm; differences are less marked when cold, which is useful to diagnose PMC. Provocative tests are therefore useful in myotonias to demonstrate muscle inexcitability, which depends on the chloride or sodium channelopathy. Muscle Nerve, 2007
Inflections in threshold electrotonus to depolarizing currents in sensory axons
Authors: Burke David , Howells James , Trevillion Louise , Kiernan Matthew C. , Bostock Hugh 
Published: July 2007

AbstractThreshold electrotonus involves tracking the changes in axonal excitability produced by subthreshold polarizing currents and is the only technique that allows insight into the function of internodal conductances in human subjects in vivo. There is often an abrupt transient reversal of the threshold change as excitability increases in response to conditioning depolarizing currents (S1 phase). In recordings from motor axons, it has been recently demonstrated that this notch or inflection is due to activation of low‐threshold axons. We report that a notch is frequently seen in sensory recordings (in 33 of 50 healthy subjects) using the standard threshold electrotonus protocol. When large, the notch can distort subsequent phases of threshold electrotonus and could complicate quantitative measurements and modeling studies. Muscle Nerve, 2007
Finite element analyses of layered visco‐elastic system under vertical circular loading
Authors: Xu Q. , Rahman M. S. 
Published: July 2007

AbstractAnalyses for the response of a linear visco‐elastic system subjected to axi‐symmetric vertical circular loading are presented. Hankel transforms with respect to the radial spatial coordinate are used to reduce the three‐dimensional problem to that involving only a single spatial dimension, which is then discretized using the finite element method. Three techniques are employed to handle the time factor in the visco‐elastic material: (i) direct time integration; (ii) Fourier transforms; and (iii) Laplace transforms. These methods are compared and evaluated through their numerical results. Copyright © 2007 John Wiley & Sons, Ltd.
Some results about f‐critical graphs
Authors: Liu Guizhen , Hou Jianfeng , Cai Jiansheng 
Published: July 2007

AbstractAn f‐coloring of a multigraph G is a coloring of the edges of E such that each color appears at each vertex v ∈ V at most f(v) times. The minimum number of colors needed to f‐color G is called the f‐chromatic index of G and is denoted by χ′f(G). Various scheduling problems on networks are reduced to finding an f‐coloring of a multigraph. Any simple graph G has f‐chromatic index equal to Δf(G) or Δf(G)+ 1, where Δf(G) = max v∈V{⌈
${d(v)\over f(v)}$⌉} and d(v) is the degree of vertex v. A connected graph G is called f‐critical if χ′f(G)=Δf(G)+1 and χ′f(G)=Δf(G−e) < χ′f(G) for any edge e ∈ E. Some results about f‐critical graphs are given. © 2007 Wiley Periodicals, Inc. NETWORKS, Vol. 50(3), 197–202 2007
The vehicle rescheduling problem: Model and algorithms
Authors: Li Jing‐Quan , Mirchandani Pitu B. , Borenstein Denis 
Published: July 2007

AbstractWhen a vehicle on a scheduled trip breaks down, one or more vehicles need to be rescheduled to serve the customers on that trip with minimum operating and delay costs. The problem of reassigning vehicles in real‐time to this cut trip as well as to other scheduled trips with given starting and ending times, is referred to as the vehicle rescheduling problem (VRSP). This paper considers modeling, algorithmic, and computational aspects of the single‐depot VRSP. The paper formulates a model for this problem and develops several fast algorithms to solve it, including parallel synchronous auction algorithms. The concept of the common feasible network (CFN) is introduced to find a good set of initial “prices” for speeding up the auction algorithm. Computational experiments on randomly generated problems are described. Computational results show that, for small problems, all of the developed algorithms demonstrate very good computational performances. For large problems, parallel CFN‐based auction algorithms provide the optimal solution with much smaller computation times. © 2007 Wiley Periodicals, Inc. NETWORKS, Vol. 50(3), 211–229 2007
A meta‐analysis of studies of nurses' job satisfaction
Authors: Zangaro George A. , Soeken Karen L. 
Published: July 2007

AbstractAlthough several variables have been correlated with nursing job satisfaction, the findings are not uniform across studies. Three commonly noted variables from the nursing literature are: autonomy, job stress, and nurse–physician collaboration. This meta‐analysis examined the strength of the relationships between job satisfaction and autonomy, job stress, and nurse–physician collaboration among registered nurses working in staff positions. A meta‐analysis of 31 studies representing a total of 14,567 subjects was performed. Job satisfaction was most strongly correlated with job stress (ES = −.43), followed by nurse–physician collaboration (ES = .37), and autonomy (ES = .30). These findings have implications for the importance of improving the work environment to increase nurses' job satisfaction. © 2007 Wiley Periodicals, Inc. Res Nurs Health 30:445–458, 2007.