bluuebunny/crossref_metadata_2025_split huggingface dataset:
Simultaneous 3D NMR spectroscopy of fluorine and phosphorus in human liver during 5‐fluorouracil chemotherapy
Authors: Li Chun‐Wei , Gonen Oded 
Published: March 2007

AbstractSimultaneous multivoxel 31P and 19F 3D localized NMR spec‐troscopy is demonstrated on a phantom and in the liver of patients undergoing bolus‐infusion 5‐fluorouracil chemotherapy. The 19F and 31P spectra were localized with 8 × 8 × 8 3D chemical‐shift imaging, with both nuclei sharing the same field of view and voxel size (27 and 64 ml in phantom and liver, respectively) using a 1.5‐Tesla clinical imager with two RF channels and a dual‐tuned surface coil. The repetition time (TR = 0.26 s) and Ernst nutation angles (θE = 32° for 19F, 28° for 31P) were chosen to optimize the signal‐to‐noise ratio (SNR) per‐untt time for the 0.5‐ to 2‐s T1 range of the 19F and 31P metabolites of interest The overall examination time, including tuning, imaging, shimming and dual‐nuclear spectroscopy, was under 90 min. Simultaneous acquisition of 31P and 19F spectra will permit the study of the influence of hepatic and/or tumor metabolism on the uptake and catabolism of fluoropyrimidine drugs with no extra measurement time.
Improving the temporal resolution of functional MR imaging using keyhole techniques
Authors: Gao Jia‐Hong , Xiong Jinhu , Lai Song , Haacke E. Mark , Woldorff Marty G. , Li Jinqi , Fox Peter T. 
Published: March 2007

AbstractUsing a keyhole technique, it is shown that the data acquisition rate of gradient‐echo imaging for functional MRI (fMRI) studies can be increased substantially. The resulting enhancement of the temporal resolution of fMRIs was accomplished without modifying the hardware of a conventional MRI system. High spatial resolution fMRI images were first collected with conventional full k‐space acquisition and image reconstruction. Using the same data set, simulation reconstruction using the keyhole principle and zero‐padding were performed for comparison with the full k‐space reconstruction. No significant changes were found for fMRI images generated from the keyhole technique with a data sharing profile of 50% of the k‐space. As k‐space data sharing profiles increased to 75 and 87.5%, the keyhole fMRI images began to show only modest changes in activation intensity and area compared with the standard images. In contrast, zero‐padding fMRI images produced a significant disparity both in activation intensity and area relative to the truly high‐resolution fMRI images. The keyhole technique's ability to retain the intensity and area of fMRI information, while substantially reducing acquisition time, makes it a promising method for fMRI studies.
Optimization of torque‐balanced asymmetric head gradient coils
Authors: Alsop David C. , Connick Thomas J. 
Published: March 2007

AbstractLocal gradient coils can improve the performance of echo‐planar, diffusion, and short TE imaging in the brain. A modified singular value decomposition algorithm, which allows the rapid optimization and comparison of designs, was employed to optimize head size gradient coils. A theoretical expression for the torque on a cylindrical coil is presented and used to design coils that are free from torque while pulsed within a magnetic field. Gradient coils of various lengths both with and without torque constraints were compared; although torque‐free coils do not perform as well as unbalanced coils, asymmetric torque‐balanced coils can achieve comparable homogeneity with only a modest Increase in inductance and resistance. Both types of coils outperform body size gradient coils by a dramatic margin. A three‐axis head gradient designed using these techniques was constructed and used for brain imaging on a clinical scanner.
Fast interleaved echo‐planar imaging with navigator: High resolution anatomic and functional images at 4 tesla
Authors: Kim Seong‐Gi , Hu Xiaoping , Adriany Gregor , Uǧurbil Kâmil 
Published: March 2007

AbstractEcho‐planar Imaging (EPI) Is sensitive to magnetic field inhomogeneities, which lead to signal loss and geometric distortions of the image. Magnetic field inhomogeneities induced by susceptibility differences, as encountered in the human body, increase with the magnetic field strength, thus, complicating implementation of high resolution EPI techniques on high magnetic field systems. These problems were overcome by using a fast multishot high resolution EPI method that uses variable flip angles, center‐out k‐space sampling, and navigator echoes. This approach maximizes signal‐to‐noise ratio, reduces flow artifacts, and permits correction of intersegment amplitude and phase variations, providing high spatial and temporal resolution. This scheme can be implemented with a single magnetization preparation for contrast that precedes the segments. The utility of this ultrafast segmented EPI technique with navigator is demonstrated for anatomic and functional imaging studies on the human brain at 4 T.
Fast 3D large‐angle spin‐echo imaging (3D FLASE)
Authors: Ma Jingfei , Wehrli Felix W. , Song Hee Kwon 
Published: March 2007

AbstractA rapid steady‐state 3D spin‐echo imaging pulse sequence, based on the principle of nutating the spins by an angle greater than 90°, has been designed and implemented on a clinical 1.5‐T whole‐body MR scanner. The pulse sequence, denoted fast large‐angle spin‐echo (FLASE), has been optimized for high‐resolution imaging of tissues with short T2 and T2*. Features of FLASE include a minimum‐phase Shinnar‐Le Roux excitation pulse and distribution of phase‐ and slice‐encoding gradients before and after the 180° refocusing pulse to minimize the critical time delay between inversion and restoration of the residual longitudinal magnetization and for minimizing echo time. A Bloch equation analysis, corroborated by experimental data, shows FLASE signal‐to‐noise to be superior to its closest analog, 3D rapid spin‐echo excitation (RASEE) (Jara et al., Magn Reson Medicine 29, 528 (1993)), and 3D gradient‐recalled acquisition in steady state (GRASS). It is demonstrated that with judicious RF phase‐cycling and steady state operation, FLASE can produce high‐quality microimages free of intravoxel phase dispersion from susceptibility‐induced background gradients. The performance of the method is exemplified with ultra high‐resolution images of trabecular bone in vitro and in vivo In the human calcaneus and wrist at voxel sizes as low as 98 × 98 × 200 μm3. Finally, the contrast behavior of refocused FLASE can be altered by disrupting the steady state analogous to gradient echo imaging.
A Modified sub‐second fast‐STEAM sequence incorporating bipolar gradients for in vivo diffusion imaging
Authors: Yongbi Martin N. , Ding Shujun , Dunn Jeffrey F. 
Published: March 2007

AbstractA modified high‐speed stimulated‐echo acquisition mode (STEAM) diffusion sequence (90°‐TE/2−90°‐TM‐[α‐TE/2‐STE]n) incorporating bipolar diffusion gradients that are less sensitive to macroscopic motion‐induced artifacts is presented. Diffusion encoding was performed only during the first echo interval (TE1) with bipolar gradients that were implemented on all three mutually orthogonal axes. Calibration measurements on phantoms filled with water, isopropanol, and dimethyl sulfoxide yielded apparent diffusion coefficients (ADC) consistent with published values. Non‐ECG‐triggered in vivo images acquired on rat brain with relatively high b values (˜450 s/mm2) indicated minimal motion artifacts. Evaluated ADCs averaged over the cortex, left mid‐brain, right mid‐brain, regions yielded (0.91 ± 0.02), (1.06 ± 0.02), (1.01 ± 0.03) × 10−3 mm2s−1, respectively.
Myocardial signal response to dipyridamole and dobutamine: Demonstration of the BOLD effect using a double‐echo gradient‐echo sequence
Authors: Li Debiao , Dhawale Paritosh , Rubin Patricia J. , Haacke E. Mark , Gropler Robert J. 
Published: March 2007

AbstractThe purpose of this study was to examine the differential myocardial signal responses due to the blood oxygen level dependent (BOLD) effect in magnetic resonance imaging (MRI) under differing conditions of myocardial oxygen supply and demand. The signal response was measured when myocardial blood flow was increased in excess of oxygen demand or when flow was increased in response to increased myocardial oxygen demand. Normal volunteers were studied using a segmented, interleaved, double‐echo, gradient‐echo sequence at baseline conditions and during pharmacological stress with either dipyridamole (n = 5) or dobutamine (n = 6). Changes in T2* in the myocardium during stress were calculated. Peak coronary flow velocity was measured at rest and during stress using a breath‐hold phase contrast technique. Administration of dipyridamole induced a 124 ± 27% increase in coronary blood flow which resulted in a 46 ± 22% increase in T2*, consistent with a decrease in myocardial venous deoxyhemoglobin concentration as myocardial oxygen supply exceeds demand. In contrast, the administration of dobutamine resulted in a 41 ± 25% increase in coronary blood flow but no significant change in T2* (−5 ± 19%), consistent with a lack of change in myocardial venous deoxyhemoglobin concentration and balanced oxygen supply and demand. Thus, alterations in the relationship between myocardial oxygen supply and demand appear to be detectable using BOLD MRI.
Observation and quantitation of lactate in oxidative and glycolytic fibers of skeletal muscles
Authors: Shen Dee , Gregory Carl D. , Dawson M. Joan 
Published: March 2007

AbstractIn 1H NMR spectroscopic studies of fatiguing skeletal muscles, two peaks consistently arise near 1.3 ppm, typically 15–20 Hz apart at 300 MHz. From a variety of NMR and biochemical evidence, both peaks are identified as lactate. Both the CH3 and CH protons of lactate experience the same shift in intact muscle; this rules out chemical bonding or complexation. The ratio of intensity of the two methyl peaks varies with muscle type and suggests a correlation with oxidative and glycolytic fiber populations. The shift can be accounted for by the presence of paramagnetic myoglobin in the oxidative fibers. Phantom studies, as well as oxygen, temperature, field, and orientation dependence of the muscle spectra are all consistent with an explanation based upon bulk magnetic susceptibility. It is concluded that the two lactate peaks represent separate contributions from glycolytic and oxidative muscle fibers.
13C‐NMR relaxation in glycogen
Authors: Overloop Kristen , Vanstapel Florent , Van Hecke Paul 
Published: March 2007

AbstractThis study is the first report on the multiexponential T2 relaxation of the 13C‐1 carbon of glycogen. In contrast to T1 relaxation, which does not display observable multiexponential decay behavior, T2 relaxation is described by a continuous distribution of T2 times. Changes in molecular weight and sample viscosity, which affect the overall mobility of the glycogen particle have little influence on T1 and T2 relaxation times. This is in contradiction with earlier results that T2 is dominated by the overall motion of the glycogen particles [L.‐H. Zang Biochemistry 29, 6815–6820 (1990)]. T1 depends strongly on the external field Bo and is almost temperature independent in the range 23–37°C whereas T2 is field independent and varies appreciably with temperature. The experimental T1 and T2 relaxation data are shown to be consistent with existing theoretical models for relaxation, suitably modified to include a distribution of correlation times for the internal motions. The presence of fast decaying components (short T2) in the FID implies broad line components in the frequency spectrum and the corresponding need to appropriately set the integration limits for the quantification of the glycogen peak.
Optimizing MRI signal‐to‐noise ratio for quadrature unmatched RF coils: Two preamplifiers are better than one
Authors: Sorgenfrei Birgit L. , Edelstein William A. 
Published: March 2007

AbstractUsing separate preamplifiers for the two outputs of a quadrature receive coil (and then combining the preamplifier outputs in a quadrature hybrid) provides a better signal‐to‐noise ratio (SNR) than is obtained by directly combining the quadrature outputs in a hybrid followed by a single preamplifier. The advantage of the two‐preamplifier configuration increases when the body coil impedance changes and is no longer matched to 50 ohms. Using 0.4 dB noise figure preamplifiers, theory predicts 1.53, 0.42, 0, 0.42, and 1.53 dB SNR advantage of the two‐preamplifier configuration over the one‐preamplifier arrangement at body coil impedances of 12.5, 25, 50, 100, and 200 ohms, respectively. Experimental hot/cold resistor noise figure measurements indicate 2.86, 0.65, 0.36, 0.83, and 1.40 dB noise figure advantage for the two preamplifier configuration relative to the one‐preamplifier configuration at those impedances. Empirical gains larger than theoretically calculated are attributable to insertion losses of various circuit elements, such as the quadrature hybrid, for the onepreamplifier configuration.
Estimation of in vivo proton intrinsic and cross‐relaxation rates in human brain
Authors: Chai Jyh‐Wen , Chen Clayton , Chen Joen Hor , Lee San‐Kan , Yeung Hong N. 
Published: March 2007

AbstractBy using on‐resonance binomial pulse saturation of the immobile component in tissues and by monitoring the time development of the longitudinal decay of the free water magnetization, it has been shown that it is possible to estimate physical model parameters not directly measurable by conventional methods. Since pulsed saturation is easy and safe to implement in a clinical MRI machine, it should be possible to estimate these parameters in vivo by the same means. In this article, we report the results of such estimates of the parameters of the principal components (gray and white matter) in brains of two normal volunteers.
Effects of blood flow modifiers on tumor metabolism observedin vivoby proton magnetic resonance spectroscopic imaging
Authors: Bhujwalla Zaver M. , Shungu Dikoma C. , Glickson Jerry D. 
Published: March 2007

AbstractPerfusion plays a key role in tumor proliferation and therapeutic response. Tumor heterogeneity necessitates use of the highest spatial resolution to monitor metabolic correlates of blood flow changes. This is best achieved with1H NMR spectroscopy, which permits noninvasive acquisition of high resolution spectroscopic images (SI) of subcutaneous tumors in a relatively short scan time (e.g., 12‐25 μl voxels with signal‐to‐noise ratio 7:1 in 30 min at 4.7 T). This study seeks to identify1H spectroscopic indices of tumor blood flow. Proton SI of subcutaneous murine RIF‐1 tumors were recorded (a) before and after administration of nicotinamide (1 g/kg) toincreaseblood flow, and (b) before and after hydralazine (10 mg/kg) todecreaseflow. Nicotinamide produced a significant decrease in the total choline peak amplitudes, which subsequent high resolution NMR spectroscopy of tumor extracts revealed to be due to decreases in phosphocholine and glycerophosphocholine. The deamidation of nicotinamide to nicotinic acid, which is known to have hypolipidemic effects and to stimulate the formation of prostaglandins, may have sufficiently altered lipid metabolism to affect thein vivoconcentration of the NMR‐visible choline‐containing compounds. The main effect of hydralazine was a significant increase of lactate, which is consistent with a reduction of tumor blood flow.
Post‐acquisition correction of MR inhomogeneities
Authors: Lee Scott K. , Vannier Michael W. 
Published: March 2007

AbstractSignal inhomogeneities in volumetric head MR scans are a major obstacle to segmentation and neuromorphometry. The fuzzy c‐means (FCM) statistical clustering algorithm was extended to estimate and retrospectively correct a multiplicative inhomogeneity field in T1‐weighted head MR scans. The method was tested on a mathematically simulated object and on seven whole head 3D MR scans. Once initial parameters governing operation of the algorithm were chosen for this class of images, results were obtained without intervention for individual MR studies. Post‐acquisition inhomogeneity correction by extended FCM clustering improved overall image uniformity and separability of gray and white matter intensities.
Institutional Alternatives to Democracy in Latin America: A Sociological Perspective
Authors: Peschard Jacqueline , Valdés Leonardo 
Published: March 2007

This paper reviews electoral studies of Latin America of the last decade, showing how elections in the context of democratic transitions have prompted reflexion on electoral behavior as well as on the nature and function of political institutions. After briefly reviewing the debate over the impact of types of democratic regimes and political party systems on political relations, the paper calls attention to the permanence in Latin America of authoritarian enclaves through which the military retain considerable maneuvering power, the influence of the international drug traffic, and the interference by strategic actors in Latin American political life. The authors conclude that democratically elected governments are far from synonymous with democratic regimes. Nevertheless, the neo-institutionalist approach which has redefined the impact of institutional design on political actions and reactions, and particularly the culturalist view among them, offers potentially fruitful explanations of why institutions and democratic practices function better in some sociocultural contexts than in others.
Foreign Language Placement: an Alternative Validation Procedure
Authors: Dalton Starrette , King Larry D. 
Published: March 2007

The validation procedure recommended by the College Entrance Examination Board (CEEB) for their foreign language placement tests determines whether individuals (1) with high and low grades in the same course, and (2) from courses at different levels, score differentially on the CEEB tests. If both these differences are statistically significant, high predictive validity is inferred. The alternative proposed in this paper is to ask the student directly upon completion of the language course to which he had been assigned, whether he had been correctly placed by the CEEB test. High predictive validity is inferred if a large proportion of the students believe that they were correctly placed. CEEB placement was evaluated by the alternative validity procedure and was found to be significantly more valid than was a second placement method in which a regression equation was used to predict level of placement from background variables. It is argued that the alternative validation procedure complements CEEB validation because in not relying on grades, it provides different information, serves different purposes, and facilitates comparisons between different placement schemes.
The Differential Aptitude Tests as Predictors of Success in a High School for Engineering Program
Authors: Omizo Michael M. 
Published: March 2007

This study examined (1) the predictive validity of the Differential Aptitude Tests (DAT) relative to achievement criteria for seniors in a high school for engineering as measured by (a) the students' ( N = 89) grades in engineering, mathematics, and science courses and (b) cumulative grade point average (CGPA) and (2) the differential validity of the 8 DAT scales in comparison of high ( N = 35) and low ( N = 54) achievers. The following selected results became apparent: (1) Numerical Ability (NA) scores were correlated .39 and .31, respectively, with performance in science courses and CGPA at the .001 level of significance and .25 with performance in mathematics courses ( p < .01); (2) Abstract Reasoning (AR) scores were correlated .46, .47, and .49, respectively, with performance in engineering, mathematics, and science courses ( p < .001) and .48 with CGPA ( p < .001); and (3) corresponding correlations of .38, .37, .49, and .44—all significant beyond the .001 level—were found between Space Relations (SR) and each of the same measures cited in the previous clause. In fulfilling the second purpose, a two-group discriminant analysis involving the 8 DAT scales yielded a canonical correlation of .88 ( p < .001) corresponding to a chi-square of 126.67 ( df = 5). The Verbal Reasoning (VR), NA, Clerical Speed and Accuracy (CSA), SR, Spelling (SP), and Language Usage (LU) scales were each valid discriminators of the high-achieving and low-achieving students (all p < .01). It was concluded that the results supported continued use of the AR scale as an admissions criterion. It was recommended that the study be replicated with similar populations and that follow-up investigations involving cross-validation be conducted for the students who decide to further their engineering programs at the college level.
Location and Interaction in Row-and-Column Seating Arrangements
Authors: Koneya Mele 
Published: March 2007

The verbal behavior, physical locations, and seat preferences of members of large groups assembled in row-and-column seating arrangements were investigated. In several trials of the experiment subjects had been categorized a priori as "high," "moderate," or "low" in respect to verbalization rates and then were randomly assigned to seats without regard for these rates. Subsequent research procedures revealed that location significantly affected the verbalization rates of the "highs" and the "moderates." Centrally located seats were associated with significantly higher verbalization rates on the part of their occupants than were noncentrally located seats. These findings confirmed the observations of previous investigators that there is an "ecology of participation" in classrooms which may make it possible to predict from which locations most verbalizations would emanate. Through the administration of a projective procedure it was also revealed that "high" verbalizers chose central seats to a greater degree and extent than did "low" verbalizers. The seat preferences of "high" and "moderate" verbalizers also differed significantly; "high" verbalizers preferred central seats to a greater extent than did "moderate" verbalizers. Some aspects of coping theory were offered as a possible explanation of this behavior.
On the Detachment of the Ends of Microfibers from the Matrix Due to Tension in the Composite
Authors: Hussain M.A. , Pu S.L. , Sadowsky M.A. 
Published: March 2007

The above title describes one of several ways in which a mechan ical failure of a composite has been observed to occur. A rigid oblong elliptic shape has been chosen for the fiber in two-dimensional treatment. Analytical formulation of the problem leads to a mixed boundary value problem of the mathematical theory of elasticity. Recent advances in reducing dual series formulations to varia tional minimization procedures (via a Fredholm integral equation of the first kind) make a mathematical analysis feasible. The variational method leads to a transcendental equation whose only real root has been evaluated by the computer for various values of the elastic constants of the matrix. The results show a substantial destruction of the bond between matrix and fiber due to the size of the detached region which ex tends over practically one-fourth of the microfiber at each end.
Shock Wave Propagation in Layered Composites
Authors: Oved Yoel , Luttwak Gabi E. , Rosenberg Zvi 
Published: March 2007

Stress histories in multilayered composite targets were recorded using manganin gages in plane impact powder gun experiments. The results exhibit an interesting resonance behavior due to the multiple wave reflections in the layers. This phenomenon is well known in com posites with periodic structure near the linear elastic region, but was not expected to be important at higher stresses, contrary to our results. Elasto-plastic calculations carried out with a finite difference pseudo- viscosity hydro-code did reproduce the experimental result and helped us to better understand the mechanism of shock wave propagation in the composites.