bluuebunny/crossref_metadata_2025_split huggingface dataset:
Wagner‐Meerwein rearrangement of a [3.3.3]‐ to a [4.3.3]propellane: deuterium tracer and conformational analysis
Authors: Reyes‐Trejo Benito , Morales‐Ríos Martha S. , Joseph‐Nathan Pedro 
Published: March 2007

AbstractFormation of (−)‐[4.3.3]propellane 4 from (−)‐14‐hydroxymodhephene (2) proceeds through a Wagner‐Meerwein rearrangement via C3C4 bond‐shift to give a stable intermediate, dimethylcyclohexadienyl cation A, which undergoes deprotonation. Herein, this mechanism was investigated by using a deuterium labeled substrate at the C‐14 methylene group of (−)‐2, which was incorporated into the C‐4 position of (−)‐[4.3.3]propellane 4. The stereostructure of (−)‐4 was investigated by applying a combination of NMR experimental and theoretical approaches. Copyright © 2007 John Wiley & Sons, Ltd.
Kallisteine A and B, two new coumarins from the roots of Peucedanum paniculatum L, a species endemic to Corsica
Authors: Vellutini Muriel , Tomi Félix , Richomme Pascal , Casanova Joseph 
Published: March 2007

AbstractFrom the dichloromethane extract of the roots of Peucedanum paniculatum L., two new coumarins, a species endemic to Corsica, have been isolated. Their structures were elucidated, on the basis of spectroscopic studies, particularly 1D and 2D NMR spectroscopy, as 6‐(7′‐β‐cyclolavandulyl)‐7‐hydroxycoumarin 1 and a spirodihydrofurano‐coumarin 2 (Kallisteine A and B). Copyright © 2007 John Wiley & Sons, Ltd.
Comparison of the BOLD‐ and EPISTAR‐technique for functional brain imaging by using signal detection theory
Authors: Siewert Bettina , Bly Benjamin Martin , Schlaug Gottfried , Darby David G. , Thangaraj Venkatesan , Warach Steven , Edelman Robert R. 
Published: March 2007

AbstractTwo magnetic resonance imaging techniques, BOLD (blood oxygenation level dependent) and EPISTAR (echo‐planar imaging and signal targeting with alternating radio‐frequency), were compared for functional brain imaging. Ten volunteers were imaged performing a sequential finger to thumb opposition task alternating with no movement conditions. Techniques were compared using variance maps and signal detection theory (ROC analysis). True positive activation in regions of interest with expected task‐dependent signal changes were computed versus false activation rates in regions in which no activation was expected. D‐prime coefficients were calculated for each comparison and statistically compared using a paired t test. Activation in the perirolandic region was seen in all volunteers with both techniques. There was no significant difference for the d‐prime between BOLD and EPISTAR. These results indicate that based on a different physiologic principle, EPISTAR is an alternative to BOLD to perform fMRI with similar results.
Magnetic resonance imaging of transverse acoustic strain waves
Authors: Muthupillai Raja , Rossman Phillip J. , Lomas David J. , Greenleaf James F. , Riederer Stephen J. , Ehman Richard L. 
Published: March 2007

AbstractWe describe a phase contrast based MRI technique with high sensitivity to cyclic displacement that is capable of quantitatively imaging acoustic strain waves in tissue‐like materials. A formalism for considering gradient waveforms as basis functions to measure arbitrary cyclic motion waveforms is introduced. Experiments with tissue‐like agarose gel phantoms show that it is possible to measure small cyclic displacements at a submicron level by an appropriate choice of the applied gradient basis function and to use this capability to observe the spatial and temporal pattern of displacements caused by acoustic strain waves. The propagation characteristics of strain waves are determined by the mechanical properties of the media. It is therefore possible to use this technique to noninvasively estimate material properties such as elastic modulus.
Off‐resonance image artifacts in interleaved‐EPI and GRASE pulse sequences
Authors: Mugler John P. , Brookeman James R. 
Published: March 2007

AbstractEcho‐time shifting (ETS) is used in GRASE and interleaved‐EPI sequences to improve the phase evolutions for off‐resonance signal sources. However, even with ETS the phase evolutions still exhibit discontinuities. In this work, we extend previous studies of ETS by quantitatively evaluating the magnitude and form of the image artifacts that result from these phase discontinuities. The functional form of the phase evolution is used to derive the general conditions under which artifacts are expected. The artifacts for two sequence structures are then evaluated as a function of off‐resonance frequency and data sampling period by calculating point spread functions and simulated images. It was found that even when ETS is used to improve the phase evolutions, periodic phase discontinuities may degrade image quality by producing ghosting artifacts of edges. These artifacts are similar to those that commonly occur with periodic motion. From our results recommendations are derived for limiting the ghosting artifacts.
OIL FLAIR: Optimized interleaved fluid‐attenuated inversion recovery in 2D fast spin echo
Authors: Listerud John , Mitchell Jim , Bagley Linda , Grossman Robert 
Published: March 2007

AbstractInversion recovery may be used to suppress signal from cerebrospinal fluid, a technique which has been named “fluid attenuated with inversion recovery” (FLAIR). This report describes interleaving a slice selective inversion pulse within a rapid spin‐echo sequence to obtain the desirable contrast characteristics of FLAIR in imaging times comparable to standard rapid spin echo. Additionally, the pulse repetition time is allowed to float above a defined minimum, which can further shorten scan times and dramatically ease the optimization process. The optimized interleaved sequence is referred to as OIL FLAIR.
Examples of the design of screened and shielded RF receiver coils
Authors: Burl Michael , Young Ian R. 
Published: March 2007

AbstractThree methods of screening RF surface coil receivers are discussed. The aim is to design coils with very much greater sensitivity on one side than on the other so that signal and noise contributions from unwanted regions of the body can be minimized. These methods can usefully be applied to situations wherein data are only wanted from one leg, although the coil is most conveniently located between the two, or from an arm lying adjacent to the body.
Quantitation of automated single‐voxel proton MRS using cerebral water as an internal reference
Authors: Soher Brian J. , Hurd Ralph E. , Sailasuta Napapon , Barker Peter B. 
Published: March 2007

AbstractData from a previously published, multi‐site trial (P. G. Webb, N. Sailasuta, S. J. Kohler, T. Raidy, R. A. Moats, R. E. Hurd, Automated single‐voxel proton MRS: technical development and multisite verification. Magn. Reson. Med. 31, 365–373 (1994)) of a fully automatic, single‐voxel, proton spectroscopy package (PROBE/SV, GE Medical Systems) was re‐analyzed in terms of absolute metabolite concentrations using the cerebral water signal as an internal reference. In 100 spectra from parietal white matter in normal volunteers ranging in age from 22 to 34 years at eight sites, overall concentrations of choline (Cho), creatine (Cr), and N‐acetyl‐aspartate (NAA) resonances were found to be 2.00 ± 0.50, 8.43 ± 1.26, and 12.55 ± 1.76 μmol/g wet weight, respectively. These values are in good general agreement with previously published values from quantitative, single‐voxel studies. Metabolite concentrations for NAA, Cr, and Cho across all sites had standard deviations of 14.1%, 14.9%, and 25.1%, respectively. Quantitation of PROBE data sets is routinely possible by using the cerebral water signal as an internal reference.
Determinants of tissue delivery for 129Xe magnetic resonance in humans
Authors: Peled Sharon , Jolesz Ferenc A. , Tseng Ching‐Hua , Nascimben Luigino , Albert Mitchell S. , Walsworth Ronald L. 
Published: March 2007

AbstractMagnetic resonance imaging using laser‐polarized 129Xe is a new technique first demonstrated by Albert et al. (Nature 370, 1994) who obtained a 129Xe image of an excised mouse lung. This paper describes the factors influencing the accumulation of inhaled, polarized 129Xe in human tissue. The resulting model predicts the 129Xe magnetization in different tissues as a function of the time from the start of inhalation, the tissue perfusion rate and partition coefficient for xenon, and the relevant T1 decay times. The relaxation times of 129Xe in biological tissues are not yet known precisely. Substitution of estimated values for these parameters results in an expected signal‐to‐noise ratio (SNR) from polarized 129Xe MR in the brain of approximately 2% of the equivalent SNR from proton MR.
Time‐resolved contrast‐enhanced 3D MR angiography
Authors: Korosec Frank R. , Frayne Richard , Grist Thomas M. , Mistretta Charles A. 
Published: March 2007

AbstractAn MR angiographic technique, referred to as 3D TRICKS (3D time‐resolved imaging of contrast kinetics) has been developed. This technique combines and extends to 3D imaging several previously published elements. These elements include an increased sampling rate for lower spatial frequencies, temporal interpolation of k‐space views, and zero‐filling in the slice‐encoding dimension. When appropriately combined, these elements permit reconstruction of a series of 3D image sets having an effective temporal frame rate of one volume every 2‐6 s. Acquiring a temporal series of images offers advantages over the current contrast‐enhanced 3D MRA techniques in that it i) increases the likelihood that an arterial‐only 3D image set will be obtained, ii) permits the passage of the contrast agent to be observed, and iii) allows temporal‐processing techniques to be applied to yield additional information, or improve image quality.
Quantification of citrate concentration in the prostate by proton magnetic resonance spectroscopy: Zonal and age‐related differences
Authors: Lowry Martin , Liney G. P. , Turnbull L. W. , Manton D. J. , Blackband S. J. , Horsman A. 
Published: March 2007

AbstractA commercial phased‐array multicoil was used to acquire water‐suppressed localized proton spectra of the two major anatomical regions of the prostate. The signal‐to‐noise ratio and spectral resolution allowed identification of peaks from choline and creatine, as well as a major peak from citrate. Quantification of the citrate peak using experimentally determined relaxation parameters with tissue water as an internal concentration reference revealed a marked variability between different volunteers. Nevertheless, in each case, the citrate concentration was up to fourfold greater in the peripheral zone than in the central gland. Furthermore, the difference in citrate concentration between these two regions was positively correlated with the subjects age. The results indicate a consistent difference in cellular function between the major anatomical regions within the prostate and may have important consequences for the application of magnetic resonance spectroscopy to the diagnosis of prostatic pathology.
A computational strategy for the deconvolution of NMR spectra with multiplet structures and constraints: Analysis of overlapping 13C‐2H multiplets of 13C enriched metabolites from cell suspensions incubated in deuterated media
Authors: Laatikainen Reino , Niemitz Matthias , Malaisse Willy J. , Biesemans Monique , Willem Rudolph 
Published: March 2007

AbstractA computational strategy for the deconvolution of complex spectra involving scalar multiplet patterns is presented. This approach fits spectra that can be composed of single resonances as well as scalar coupling multiplets for which resonance frequencies, intensities, and lineshape parameters can be optimized. For multiplets, the coupling constant also is optimized. Any external information about the optimizable parameters can be taken into account as external constraints. A lineshape described by absorptive and dispersive Lorentzian and Gaussian contributions and the baseline with up to 40 Fourier and polynomial terms can likewise be optimized. The effectiveness of the procedure is assessed on the basis of computer simulated deconvolutions of a composite of 1J(13C−2H) multiplets arising from a mixture of all possible 13C−2H isotopomers of deuterated L‐[3‐13C]lactate generated from cell preparations incubated with D‐[1‐13C]glucose in D2O, which was analyzed previously with a manual deconvolution procedure (R. Willem, M. Biesemans, F. Kayser, W. J. Malaisse, Magn. Reson. Med. 31, 259–267 (1994)). The use of constraints is shown to lead to an improvement in the results. The fitting strategies and the importance of the baseline as an origin of bias are discussed.
An evaluation of the effects of susceptibility changes on the water chemical shift method of temperature measurement in human peripheral muscle
Authors: Young Ian R. , Hajnal Joseph V. , Roberts Idris G. , Ling Junxiao X. , Hill‐Cottingham Roger J. , Oatridge Angela , Wilson Jason A. 
Published: March 2007

AbstractDivergencies between chemical shift measurements of temperature and directly measured values using optical sensors have been studied in vivo in human peripheral muscle with the assistance of a variety of experimental and theoretical techniques. These include the modeling of both thermal and susceptibility changes using two‐ and three‐dimensional finite element methods, as well as the use of multi‐wavelength near infrared observations. The conclusion of these studies is that a simple temperature calibration is not accessible, with results affected by the complex response of the tissue itself.
A method to improve the BO homogeneity of the heart in vivo
Authors: Jaffer Farouc A. , Wen Han , Balaban Robert S. , Wolff Steven D. 
Published: March 2007

AbstractA homogeneous static (Bo) magnetic field is required for many NMR experiments such as echo planar imaging, localized spectroscopy, and spiral scan imaging. Although semi‐automated techniques have been described to improve the Bo field homogeneity, none has been applied to the in vivo heart. The acquisition of cardiac field maps is complicated by motion, blood flow, and chemical shift artifact from epicardial fat. To overcome these problems, an ungated three‐dimensional (3D) chemical shift image (CSI) was collected to generate a time and motion‐averaged Bo field map. Bo heterogeneity in the heart was minimized by using a previous algorithm that solves for the optimal shim coil currents for an input field map, using up to third‐order current‐bounded shims (1). The method improved the Bo homogeneity of the heart in all 11 normal volunteers studied. After application of the algorithm to the unshimmed cardiac field maps, the standard deviation of proton frequency decreased by 43%, the magnitude 1H spectral linewidth decreased by 24%, and the peak‐peak gradient decreased by 35%. Simulations of the high‐order (second‐ and third‐order) shims in Bo field correction of the heart show that high order shims are important, resulting for nearly half of the improvement in homogeneity for several subjects. The T2* of the left ventricular anterior wall before and after field correction was determined at 4.0 Tesla. Finally, results show that cardiac shimming is of benefit in cardiac 31P NMR spectroscopy and cardiac echo planar imaging.
Improved centric phase encoding orders for three‐dimensional magnetization‐prepared mr angiography
Authors: Wilman Alan H. , Riederer Stephen J. 
Published: March 2007

AbstractNew centric phase encoding orders are introduced for transient state three‐dimensional MR imaging. Unlike previous centric orders, these variants are not fixed with respect to differences in the relative y and z fields of view, but are tailored to account for the differential degrees of gradient dephasing in the ky and kz phase encoding directions and thus maintain the highest weighting for the most central k‐space values. The new centric orders are compared with previous methods in both simulation and experimental magnetization‐prepared MR angiography of the carotid and renal arteries. In comparison with other tested centric orders, the new methods provided better retention of true vessel shape caused by isotropic blurring across the phase encoding plane. In addition, the new methods provided increased contrast, with the degree of improvement over previous methods depending on vessel orientation, size, and degree of inflow.
Apparent diffusion coefficients in benign and secondary progressive multiple sclerosis by nuclear magnetic resonance
Authors: Horsfield Mark A. , Lai Ming , Webb Stephanie L. , Barker Gareth J. , Tofts Paul S. , Turner Robert , Rudge Peter , Miller David H. 
Published: March 2007

AbstractThe diffusion characteristics of water in brain white matter were studied in patients with benign and secondary progressive multiple sclerosis (MS), and also in normal controls. In the MS patients, both lesions and normal‐appearing white matter (NAWM) were examined to assess whether pathological differences might be evident from the diffusion behavior. A volume‐selective technique was used to reduce data acquisition time and improve the reliability and precision of the measurements. This also allowed the time‐dependence of apparent diffusion coefficients to be assessed. While lesions from both patient groups showed an elevated diffusion coefficient, no differences between the two groups were found. In addition, NAWM was elevated for both patient groups compared with the control group, although this was only statistically significant for patients with a benign disease course. The degree of elevation of the diffusion coefficient within the individual lesions measured was not related to the disability of the patient. Pathological differences between lesions in patients with different disease courses, if they exist, have not been detected in this study of brain water diffusion.
Design of adiabatic selective pulses using optimal control theory
Authors: Rosenfeld Daniel , Zur Yuval 
Published: March 2007

AbstractOptimal control theory has been applied in the past for the design of RF pulses for selective excitation. This was the outcome of having established the controllability of the MR spin system for the selective excitation problem. “Minimum distance” was the main formulation used for the solution. Because of their robust behavior in the presence of inhomogeneous RF fields, adiabatic pulses play an important role in spin inversion and excitation. In this study, we present a method for incorporating adiabaticity into the optimal control problem by enhancing the cost functional with an appropriate term. Two different types of adiabatic terms are proposed. Furthermore, two methods are used to solve the optimal control problem, namely the Hamiltonian approach and the solution by mathematical programming. Design examples include both a frequency selective pulse for performing fat suppression by inversion and a regular inversion pulse. It is shown that, in the course of optimization, the pulse designer can trade‐off slice resolution against pulse adiabaticity.
Recordings of eye movements for stimulus control during fMRI by means of electro‐oculographic methods
Authors: Felblinger Jacques , Müri René M. , Ozdoba Christoph , Schroth Gerhard , Hess Christian W. , Boesch Chris 
Published: March 2007

AbstractA method for monitoring eye movements in humans during functional MRI is presented. It is based on the acquisition of electro‐oculographic (EOG) signals near one eye. EOG potentials were amplified and converted into an optical signal just outside the head coil. An optical fiber was used for signal transmission from inside the magnet bore to the control room. The EOG sensor was tested during EPI sequences at 1.5 Tesla without contamination of the MR signal. Some flow related artifacts on the EOG were observed inside the magnet, but no additional interactions from the MR sequence. An analysis of the latency, direction, and amplitude of the saccadic eye movements was possible.
Contribution of Sinerem® used as blood‐pool contrast agent: Detection of cerebral blood volume changes during apnea in the rabbit
Authors: Berry Isabelle , Benderbous Soraya , Ranjeva Jean‐Philippe , Gracia‐Meavilla Dominique , Manelfe Claude , Le Bihan D. 
Published: March 2007

AbstractThe authors suggest that ultra‐small paramagnetic iron oxide (USPIO) particles used as blood pool contrast agents may increase the sensitivity of midfield MRI (i.e., less than 1.5 Tesla) to physiological variations in cerebral blood volume. This hypothesis was tested on a rabbit model of apnea which increases pCO2 and cerebral blood volume. Using Sinerem® as the USPIO at a blood concentration of 60 μmol iron/kg body weight, an 8% T2*‐weighted signal decrease could be observed at 1.0 T with 25–33% increase in pCO2. Comparatively, in the absence of USPIO, T2*‐weighted signal dropped only 4% during apnea and after mild hyperoxygenation beforehand, due to increased deoxyhemoglobin content. These preliminary data suggest that USPIOs could play an important role in functional MRI at midfield strength, by sensitizing the signal to cerebral blood volume changes.
Influence of membrane lipid packing on T2‐weighted magnetic resonance images: Study of relaxation parameters in model membrane systems
Authors: Lee Jumi , Barry Judith A. 
Published: March 2007

AbstractThe detailed mechanisms leading to soft tissue contrast in MRI are not known. To explore the physical basis for this phenomena, the effect of acyl chain packing of phospholipid model membranes on water proton relaxation were investigated at 20 MHz at 40°C. Three variables affecting lipid packing were examined: chain composition, toluene concentration, and pH/ionic strength. It is demonstrated that the T2 of water protons is strongly influenced by changes in lipid packing, while T1 is generally insensitive to these variables. It is also shown that small changes in water content (7 wt%) altered both T1 and T2 in all systems studied. The results suggest that the physical properties of biological membranes in tissues are an important factor in determining T2.
A comparison of phase encoding ordering schemes in T2‐weighted GRASE imaging
Authors: Johnson Glyn , Feinberg David A. , Venkataraman Viswanathan 
Published: March 2007

AbstractGradient and spin echo (GRASE) imaging is an echo train imaging sequence that combines gradient and RF refocusing. This combination introduces phase modulations into the echo train. If the phase encoding order is linear with echo time, these modulations cause severe ghosting artifacts. Changing the order of phase encoding can greatly reduce these artifacts. Several phase encoding orders for T2‐weighted sequences are compared in this paper: linear, partially randomized, standard GRASE ordering, and k‐banded (kb) GRASE ordering. Different possible implementations of GRASE and kbGRASE are also considered. Computer simulation is used to compare resolution and artifact levels. Phantom and volunteer images are presented. The linear order is most sensitive to ghosting artifacts associated with chemical shift, susceptibility differences and static field inhomogeneities. The standard GRASE order is least sensitive to these but most vulnerable to artifacts associated with short T2 signals. kbGRASE is a good intermediate between linear and standard GRASE and generally shows the lowest artifact levels. The partially randomized order gives the most diffuse artifacts. Computer simulations show that spatial resolution and contrast with all phase encoding orders are similar.