bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stimulation of estradiol glucuronidation: A protective mechanism against estradiol‐mediated carcinogenesis?
Authors: Pfeiffer Erika , Graf Eva , Gerstner Silke , Metzler Manfred 
Published: April 2006

Abstract17β‐Estradiol (E2) and its catechol and methoxy metabolites are believed to play important roles in the mechanism of E2–mediated tumor formation. Because conjugation with glucuronic acid lowers tissue levels by facilitating excretion, we have determined the kinetic parameters of the glucuronidation of E2, estrone (E1), and seven phase I metabolites using human liver microsomes. The catechol estrogens 2‐ and 4‐hydroxy‐E2/E1 exhibited the highest clearance, exceeding that of E2, E1, and the methoxy metabolites by factors of 6–44. Homotropic activation kinetics were observed for the 3‐glucuronidation of E2 but not for any of the metabolites. None of the metabolites affected the kinetics of the 3‐glucuronidation of E2. In contrast, the isoflavone daidzein stimulated the formation of E2‐3‐glucuronide, as has been reported previously. This heterotropic activation by daidzein appears to be specific for the glucuronidation of E2 because daidzein did not affect the glucuronidation of the 2‐ and 4‐hydroxy metabolites of E2. However, daidzein may lower the glucuronidation of 2‐methoxy‐E2in vivodue to its preferential glucuronidation. The decreased tissue levels of E2 and increased concentrations of 2‐methoxy‐E2, as implied by this study and the previous one, may contribute to the protective effect of daidzein against breast and endometrial cancer.
Cytotoxic and antimitotic effects of N‐containing Monascus metabolites studied using immortalized human kidney epithelial cells
Authors: Knecht Anja , Humpf Hans‐Ulrich 
Published: April 2006

AbstractRecently the first Monascus metabolites with a pyridine ring were detected, the monascopyridines A and B. They are formally dehydrogenated derivatives of the red rice pigments rubropunctamine and monascorubramine. Because of their structural similarity, the toxicological effects of these secondary metabolites were studied using immortalized human kidney epithelial cells. The cytotoxicity was determined with the following different endpoint detection methods: metabolic activity, trypan blue exclusion, and electronic cell counting. The compounds led to EC50 values between 11 and 31 μmol/L but the pigments caused a stronger reduction of the cell viability. Also, the apoptotic potential was examined by measuring caspase 3 activity and detecting apoptotic bodies, but none of the tested compounds induced apoptosis. All four substances caused a rise of the mitotic index to about 9% (100 μmol/L monascopyridine A and B) and 20% (25 μmol/L rubropunctamine and monascorubramine). The significant decrease of the ratio of cells in the ana‐ and telophase to cells in the prometa‐ and metaphase proved a stop of the mitosis at the meta‐ to anaphase control point. The compounds caused mitotic arrest and the formation of structural damages like c‐mitosis through interaction with the mitotic spindle. These effects point to an aneuploidy inducing potential, which is linked to cancer formation.
Structure elucidation of a new friedelane triterpene from the mangrove plant Hibiscus tiliaceus
Authors: Li Liya , Huang Xueshi , Sattler Isabel , Fu Hongzheng , Grabley Susanne , Lin Wenhan 
Published: April 2006

AbstractFrom the stem and bark of the mangrove plant Hibiscus tiliaceus, a new friedelane‐type triterpene named 27‐oic‐3‐oxo‐28‐friedelanoic acid (1) together with eight known triterpenoids involving five friedelane‐type derivatives was isolated. The structure of 1 was determined by extensive 2D NMR (DQF‐COSY, HMQC, HMBC, and NOESY) data analyses. All the compounds were obtained from mangrove plants for the first time. Copyright © 2006 John Wiley & Sons, Ltd.
Correction of systematic errors in CORE processing of DOSY data
Authors: Nilsson Mathias , Morris Gareth A. 
Published: April 2006

AbstractDOSY data for mixtures are commonly processed either by single channel methods (e.g. HR‐DOSY) or multichannel methods (e.g. CORE). Both aim to separate the signals from species of different molecular sizes by their diffusion coefficients; the result is displayed either as a 2D plot (as in HR‐DOSY) or as individual spectra (as in CORE). Both types of methods are sensitive to any systematic errors in the experimental data. The effects of, and remedies for, two such sources of error, spatially non‐uniform pulsed field gradients (PFGs) and instrument instability, are demonstrated for CORE processing, using a corrected form of the Stejskal–Tanner equation and reference deconvolution, respectively. Copyright © 2006 John Wiley & Sons, Ltd.
Solvent effect in 1H NMR spectra of 3′‐hydroxy‐4′‐methoxy isoflavonoids from Astragalus membranaceus var. mongholicus
Authors: Du Xingang , Bai Yanjing , Liang Hong , Wang Zhiying , Zhao Yuying , Zhang Qingying , Huang Luqi 
Published: April 2006

AbstractFour 3′‐hydroxy‐4′‐methoxy‐isoflavonoids: calycosin‐7‐O‐β‐D‐glucopyranoside (1), calycosin (2), pratensein‐7‐O‐β‐D‐glucopyranoside (3), and pratensein (4) were isolated from Astragalus membranaceus var. mongholicus, among which compound 4 was obtained from this plant for the first time. The solvent effect obscuring 1H signal patterns of B ring of compounds 1–4 was reported to avoid mis‐assignments. Previously reported NMR data of compounds 1 and 2 were corrected based on 1D and 2D NMR experiments. Copyright © 2006 John Wiley & Sons, Ltd.
Density‐functional computation of 53Cr NMR chemical shifts
Authors: Bühl Michael 
Published: April 2006

Abstract53Cr chemical shifts of CrO42−, Cr2O72−, CrO3X−, CrO2X2(X = F, Cl), and Cr(CO)5L (L = CO, PF3, CHNH2, CMeNMe2) are computed, using geometries optimized with the gradient‐corrected BP86 density functional, at the gauge‐including atomic orbitals (GIAO)‐, BPW91‐, and B3LYP levels. For this set of compounds, substituent effects on δ(53Cr) are better described with the pure BPW91 functional than with B3LYP, in contrast to most other transition‐metal chemical shifts studied so far. For selected cases, 53Cr NMR line widths can be rationalized in terms of electric field gradients (EFGs) computed with the BPW91 functional, but in general other factors such as molecular correlation times appear to be dominating. 53Cr chemical shifts and EFGs are predicted for CrO3, Cr(C6H6)2, Cr(C6H6)CO3, and, with reduced reliability, for Cr2(µ2‐O2CH)4. Copyright © 2006 John Wiley & Sons, Ltd.
Changing body temperature affects the T signal in the rat brain and reveals hypothalamic activity
Authors: Vanhoutte G. , Verhoye M. , Van der Linden A. 
Published: April 2006

AbstractThis study was designed to determine brain activity in the hypothalamus—in particular the thermoregulatory function of the hypothalamic preoptic area (PO). We experimentally changed the body temperature in rats within the physiological range (37–39°C) and monitored changes in blood oxygenation level‐dependent (BOLD) MR signal. To explore PO activity we had to deal with general signal changes caused by temperature‐dependent alterations in the affinity of oxygen for hemoglobin, which contributes to BOLD contrast because it is partly sensitive to the amount of paramagnetic deoxyhemoglobin in the voxel. To reduce these overall temperature‐induced effects, we corrected the BOLD data using brain‐specific correction algorithms. The results showed activity of the PO during body warming from 38°C to 39°C, supported by an increased BOLD signal after correction. This is the first fMRI study on the autonomous nervous system in which hypothalamic activity elicited by changes in the internal environment (body temperature) was monitored. In this study we also demonstrate 1) that any fMRI study of anesthetized small animals should guard against background BOLD signal drift, since animals are vulnerable to body temperature fluctuations; and 2) the existence of a link between PO activity and the sympathetically‐mediated opening of the arteriovenous anastomoses in a parallel study on the rat tail, a peripheral thermoregulatory organ. Magn Reson Med, 2006. © 2006 Wiley‐Liss, Inc.
Quantitative lung perfusion mapping at 0.2 T using FAIR True‐FISP MRI
Authors: Martirosian Petros , Boss Andreas , Fenchel Michael , Deimling Michael , Schäfer Jürgen , Claussen Claus D. , Schick Fritz 
Published: April 2006

AbstractPerfusion measurements in lung tissue using arterial spin labeling (ASL) techniques are hampered by strong microscopic field gradients induced by susceptibility differences between the alveolar air and the lung parenchyma. A true fast imaging with steady precession (True‐FISP) sequence was adapted for applications in flow‐sensitive alternating inversion recovery (FAIR) lung perfusion imaging at 0.2 Tesla and 1.5 Tesla. Conditions of microscopic static field distribution were assessed in four healthy volunteers at both field strengths using multiecho gradient‐echo sequences. The full width at half maximum (FWHM) values of the frequency distribution for 180–277 Hz at 1.5 Tesla were more than threefold higher compared to 39–109 Hz at 0.2 Tesla. The influence of microscopic field inhomogeneities on the True‐FISP signal yield was simulated numerically. Conditions allowed for the development of a FAIR True‐FISP sequence for lung perfusion measurement at 0.2 Tesla, whereas at 1.5 Tesla microscopic field inhomogeneities appeared too distinct. Perfusion measurements of lung tissue were performed on eight healthy volunteers and two patients at 0.2 Tesla using the optimized FAIR True‐FISP sequence. The average perfusion rates in peripheral lung regions in transverse, sagittal, and coronal slices of the left/right lung were 418/400, 398/416, and 370/368 ml/100 g/min, respectively. This work suggests that FAIR True‐FISP sequences can be considered appropriate for noninvasive lung perfusion examinations at low field strength. Magn Reson Med, 2006. © 2006 Wiley‐Liss, Inc.
Continuously moving table 3D MRI with lateral frequency‐encoding direction
Authors: Aldefeld Bernd , Börnert Peter , Keupp Jochen 
Published: April 2006

AbstractA method is presented for 3D MRI in an extended field of view (FOV) based on continuous motion of the patient table and an efficient acquisition scheme. A gradient‐echo MR pulse sequence is applied with lateral (left–right (L/R)) frequency‐encoding direction and slab selection along the direction of motion. Compensation for the table motion is achieved by a combination of slab tracking and data alignment in hybrid space. The method allows fast k‐space coverage to be achieved, especially when a short sampling FOV is chosen along the direction of table motion, as is desirable for good image quality. The method can be incorporated into different acquisitions schemes, including segmented k‐space scanning, which allows for contrast variation with the use of magnetization preparation. Head‐to‐toe images of volunteers were obtained with good quality using 3D spoiled gradient‐echo sequences. As an example of magnetization‐prepared imaging, fat/water separated images were acquired using chemical shift selective (CHESS) presaturation pulses. Magn Reson Med, 2006. © 2006 Wiley‐Liss, Inc.
Partial‐k‐space acquisition method for improved SNR efficiency and temporal resolution in 3D fMRI
Authors: Hu Y. , Glover G.H. 
Published: April 2006

AbstractPrevious studies have shown the relative importance of physiological noise and thermal noise in 2D MR images. Since physiological noise is proportional to the signal, it can be the dominant component at the center of k‐space. In this study we demonstrate that the signal‐to‐noise ratio (SNR) efficiency and temporal resolution for 3D functional MRI (fMRI) are increased by the use of a partial‐k‐space acquisition method. In partial‐k‐space methods, the high‐spatial‐frequency components are doubled in amplitude during reconstruction, resulting in twice as much noise from those components. However, in sum these contributions are relatively small compared to those at the low spatial frequencies, where physiological noise is dominant. Therefore, the effect on the final MR images is almost negligible due to the square summation rule. Thus, the partial‐k‐space 3D method sacrifices much less SNR than is expected from the thermal noise model, and the SNR efficiency is increased compared to a full‐k‐space acquisition since more time frames can be collected for the same scan time. Accordingly, the temporal resolution can be increased in 3D acquisitions because only partial coverage of k‐space is necessary. Experimental results confirm that more activation with a higher average t‐score is detected by this method. Magn Reson Med, 2006. © 2006 Wiley‐Liss, Inc.
Respiration‐induced B0field fluctuation compensation in balanced SSFP: Real‐time approach for transition‐band SSFP fMRI
Authors: Lee Jongho , Santos Juan M. , Conolly Steven M. , Miller Karla L. , Hargreaves Brian A. , Pauly John M. 
Published: April 2006

AbstractIn functional MRI (fMRI) the resonance frequency shift induced from respiration is a major source of physiological noise. In transition‐band SSFP fMRI the respiration‐induced resonance offset not only increases noise interference, it also shifts the activation band. This leads to a reduction in the contrast‐to‐noise ratio (CNR) and the potential for varying contrast levels during the experiment. A novel real‐time method that compensates for the respiration‐induced resonance offset frequency is presented. This method utilizes free induction decay (FID) phase information to measure the resonance offset. For compensation, one can update the resonant frequency in real time by changing the transmit RF pulse and receiver phases to track the measured offset. The results show decreased signal power in the respiration frequency band and increased numbers of activated voxels with higher Z‐scores compared to uncompensated experiments. Magn Reson Med, 2006. © 2006 Wiley‐Liss, Inc.
Simultaneous outer volume and blood suppression by quadruple inversion‐recovery
Authors: Yarnykh Vasily L. , Yuan Chun 
Published: April 2006

AbstractA new method has been developed for reduced field‐of‐view (FOV) imaging with simultaneous blood suppression. This method combines suppression of signals from the outer volume and inflowing blood by using a small‐FOV quadruple inversion‐recovery (SFQIR) preparative pulse sequence consisting of two double‐inversion pulse pairs separated by appropriate delays. Within each pair, inversion pulses are successively applied to the imaged slice and the slab orthogonal to the imaging plane with the thickness equal to the FOV size in the phase‐encoding direction. Each double inversion results in the reinversion of the magnetization in the central part of the FOV, while the outer areas of the FOV and inflowing blood remain inverted. The SFQIR module was implemented for single‐ and multislice acquisition with a fast spin‐echo readout sequence. Based on a theoretical model of the signal, the timing parameters of the sequence corresponding to the maximal suppression efficiency can be found by minimizing the variation of the normalized signal over the entire range of T1's that occur in tissues. The method was tested for black‐blood imaging of the aorta and carotid arteries, and the results demonstrated its ability to eliminate motion and flow artifacts, reduce scan time, and improve spatial resolution. Magn Reson Med, 2006. © 2006 Wiley‐Liss, Inc.
Combo acquisitions: Balancing scan time reduction and image quality
Authors: Mekle Ralf , Wu Ed X. , Meckel Stephan , Wetzel Stephan G. , Scheffler Klaus 
Published: April 2006

AbstractRecently a new technique for the combined acquisition of multicontrast images, termed “combo acquisition,” was introduced. In combo acquisitions, the three concepts of 1) variable acquisition parameters, 2) k‐space data sharing, and 3) multicontrast imaging are systematically integrated to reduce MRI scan time and improve data utilization in a clinical setting. In this study, two‐contrast and three‐contrast spin‐echo (SE) and turbo spin‐echo (TSE) combo acquisition protocols that were designed and optimized in simulation experiments were implemented on a 1.5 T clinical scanner. Phantom and human brain data from volunteers and patients were acquired. Scan time reductions of 25–52% were achieved compared to standard acquisitions, largely confirming the simulation results. We evaluated the resulting images by quantitatively analyzing the preservation of contrast and the signal‐to‐noise ratio (SNR). In addition, data sets for 10 clinical cases obtained with TSE combo and corresponding standard acquisitions were graded by two experienced neuroradiologists in terms of the level of artifacts and image quality for comparison. Only minor image degradation with the combo scans was observed, indicating an inherent trade‐off between scan time reduction and image quality. The specific aspects of combo acquisitions with respect to motion, flow, and k‐space data weighting are discussed. Magn Reson Med, 2006. © 2006 Wiley‐Liss, Inc.
Liposome‐enhanced MRI of neointimal lesions in the ApoE‐KO mouse
Authors: Mulder Willem J.M. , Douma Kim , Koning Gerben A. , van Zandvoort Marc A. , Lutgens Esther , Daemen Mat J. , Nicolay Klaas , Strijkers Gustav J. 
Published: April 2006

AbstractConventional high‐resolution MRI is capable of detecting lipid‐rich atherosclerotic plaques in both human atherosclerosis and animal models of atherosclerosis. In this study we induced neointimal lesions in ApoE‐KO mice by placing a constrictive collar around the right carotid artery. The model was imaged with conventional multispectral MRI, and the thickened wall could not be distinguished from surrounding tissue. We then tested paramagnetic liposomes (mean size = 90 nm) for their ability to improve MRI visualization of induced thickening, using Gd‐DTPA as a control. T1‐weighted (T1‐w), black‐blood MRI of the neck area of the mice was performed before and 15 min, 45 min, and 24 hr after intravenous injection of either paramagnetic liposomes or Gd‐DTPA. The collared vessel wall of mice that were injected with liposomes showed a pronounced signal enhancement of ∼100% immediately after injection, which was sustained largely until 24 hr postinjection. In contrast, the vessel wall of all controls (left carotid artery and animals injected with Gd‐DTPA) did not show significant contrast enhancement at those time points. This study demonstrates that intimal thickening in ApoE‐KO mice can be effectively detected by contrast‐enhanced (CE)‐MRI upon injection of paramagnetic liposomes. Magn Reson Med, 2006. © 2006 Wiley‐Liss, Inc.
Measurement of kinetic parameters in skeletal muscle by magnetic resonance imaging with an intravascular agent
Authors: Faranesh Anthony Z. , Kraitchman Dara L. , McVeigh Elliot R. 
Published: April 2006

AbstractThe purpose of this work was to investigate the use of an intravascular contrast agent to determine perfusion kinetics in skeletal muscle. A two‐compartment kinetic model was used to represent the flux of contrast agent between the intravascular space and extravascular extracellular space (EES). The relationship between the image signal‐to‐noise ratio (SNR) and errors in estimating permeability surface area product (Ktrans), interstitial volume (ve), and plasma volume (vp) for linear and nonlinear curve‐fitting methods was estimated from Monte Carlo simulations. Similar results were obtained for both methods. For an image SNR of 60, the estimated errors in these parameters were 10%, 22%, and 17%, respectively. In vivo experiments were conducted in rabbits to examine physiological differences between these parameters in the soleus (SOL) and tibialis anterior (TA) muscles in the hind limb. Values for Ktrans were significantly higher in the SOL (3.2 ± 0.9 vs. 2.0 ± 0.5 × 10–3 min–1), as were values for vp (3.4 ± 0.8 vs. 2.1 ± 0.7%). Differences in ve for the two muscles (8.7 ± 2.2 vs. 8.5 ± 1.6%) were not found to be significant. These results demonstrate that relevant physiological metrics can be calculated in skeletal muscle using MRI with an intravascular contrast agent. Magn Reson Med, 2006. Published 2006 Wiley‐Liss, Inc.
Toward quantitative short‐echo‐time in vivo proton MR spectroscopy without water suppression
Authors: Dong Zhengchao , Dreher Wolfgang , Leibfritz Dieter 
Published: April 2006

AbstractA methodological development for quantitative short‐echo‐time (TE) in vivo proton MR spectroscopy (MRS) without water suppression (WS) is described that integrates experimental and software approaches. Experimental approaches were used to eliminate frequency modulation sidebands and first‐order phase errors. The dominant water signal was modeled and extracted by the matrix pencil method (MPM) and was used as an internal reference for absolute metabolite quantification. Spectral fitting was performed by combining the baseline characterization by a wavelet transform (WT)‐based technique and time‐domain (TD) parametric spectral analysis using full prior knowledge of the metabolite model spectra. The model spectra were obtained by spectral simulation instead of in vitro measurements. The performance of the methodology was evaluated by Monte Carlo (MC) studies, phantom measurements, and in vivo measurements on rat brains. More than 10 metabolites were quantified from spectra measured at TE = 20 ms on a 4.7 T system. Magn Reson Med, 2006. © 2006 Wiley‐Liss, Inc.
Selective and nonselective benzodiazepine agonists have different effects on motor cortex excitability
Authors: Mohammadi Bahram , Krampfl Klaus , Petri Susanne , Bogdanova Dessislava , Kossev Andon , Bufler Johannes , Dengler Reinhard 
Published: April 2006

AbstractTranscranial magnetic stimulation (TMS) is a useful method to study pharmacological effects on motor cortex excitability. Zolpidem is a selective agonist of the benzodiazepine receptor subtype BZ1and has a distinct pharmacological profile compared to diazepam. To study the different effects of these two drugs on the cortical inhibitory system, TMS was performed before and after administration of a single oral dose of zolpidem (10 mg) and diazepam (5 mg) in six healthy volunteers. TMS tests included the determination of resting and active motor threshold (MT) and measurements of the amplitudes of motor evoked potentials, intracortical facilitation (ICF), short‐latency intracortical inhibition (SICI), and long‐latency intracortical inhibition (LICI), and determination of the cortical silent period (CSP). Both drugs were without effect on the active or resting MT and decreased the ICF. Prolongation of the CSP and enhancement of LICI only in the presence of zolpidem point to a specific BZ1‐related mechanism underlying the long‐lasting component of cortical inhibition. This selective modulation of the CSP and the LICI points to a specific role of BZ1receptors in the control of inhibitory neuronal loops within the primary motor cortex. Muscle Nerve, 2006
Fully sequential indifference‐zone selection procedures with variance‐dependent sampling
Authors: Jeff Hong L. 
Published: April 2006

AbstractFully sequential indifference‐zone selection procedures have been proposed in the simulation literature to select the system with the best mean performance from a group of simulated systems. However, the existing sequential indifference‐zone procedures allocate an equal number of samples to the two systems in comparison even if their variances are drastically different. In this paper we propose new fully sequential indifference‐zone procedures that allocate samples according to the variances. We show that the procedures work better than several existing sequential indifference‐zone procedures when variances of the systems are different. © 2006 Wiley Periodicals, Inc. Naval Research Logistics, 2006