bluuebunny/crossref_metadata_2025_split huggingface dataset:
13C NMR investigation of synovial fluids
Authors: Albert Klaus , Michele Sabine , Günther Ulrich , Fial Manfred , Gall Hugo , Saal Johannes 
Published: March 2007

Abstract13C NMR spectra of synovial fluids from 20 patients suffering from rheumatic diseases have been recorded. Structural changes in hyaluronic acid, the main carrier of the viscoelastic properties of synovial fluid, could be observed in the NMR spectra of the native biological fluid. By comparing these spectra with those of purified hyaluronic acid, a rough estimation of the degree of depolymerization of synovial hyaluronlic acid was possible. The patients with rheumatoid arthritis appeared to have a lower degree of polymerization compared to patients with osteoarthrosis. Thus, 13C NMR spectroscopy prolvides useful information about biophysical properties of sartorial fluid.
Self‐correction of proton spectroscopic images for gradient eddy current distortions and static field inhomogeneities
Authors: Johnson G. , Jung K. J. , Wu E. X. , Hilal S. K. 
Published: March 2007

AbstractA postprocessing method of correcting for gradient eddy current distortions and inter‐voxel static field inhomogeneities in spectroscopic imaging is presented. Data is acquired normally and all spatial processing is performed. The FID k each voxel is then digitally filtered to extract the signal from a signal reference line. Phase multiplying the original FID by the phase of this reference signal corrects for gradient eddy currents and static field offsets. Computer simulations show that the method is robust with respect to noise, filter bandwidth and the presence of small lines close to the reference line. The method is demonstrated on proton spectroscopic images of phantoms.
Magnetization‐prepared cardiac imaging using gradient echo acquisition
Authors: Liu Yu , Riederer Stephen J. , Ehman Richard L. 
Published: March 2007

AbstractMagnetization‐prepared 2DFT and 3DFT gradlent echo techniques are presented for acquisition of black blood cardiac images. Both methods incorporate RF pulses for blood saturation, centric or centric‐like view ordering, data acquisition during late dlastole, and breath‐holding. In a series of 13 volunteer studies, these methods have consistently provided good visuallzation of intraventricular structures.
Gadolinium enhancement in acute and chronic‐progressive experimental allergic encephalomyelitis in the guinea pig
Authors: Karlik S. J. , Grant E. A. , Lee D. , Noseworthy J. H. 
Published: March 2007

AbstractMagnetic resonance imaging detects blood‐brain barrier disruption after gadolinium‐DTPA enhancement of central nervous system lesions of multiple sclerosis. Experimental allergic encephalomyelitis has many clinical and pathological features in common with multiple sclerosis including alterations in the integrity of the blood‐brain barrier. We have compared T2‐weighted cranial MR images with Gd‐DTPA dimeglumine‐enhanced T1‐weighted images of myelin bask protein‐induced acute (Days 8–42 postimmunlzation) and central nervous system‐induced chronic‐progressive (Days 70–95 post immunization) forms of experimental allergic encephalomyelitis in the guinea pig. Although animals from both groups had abnormal T2‐weighted images, only the myelin bask protein‐acute‐EAE animals (Days 14–24 postimmunlzation) showed enhancement on postcontrast MR studies. The different responses of the acute and chronic diseases may result from different immunogens, severity of disease, or different permeability of the blood‐brain barrier. Therefore, gadolinium‐DTPA‐enhanced, T1‐weighted MR images distinguish acutely active and chronic inflammatory lesions in experimental allergic encephalomyelitis.
4 Tesla gradient recalled echo characteristics of photic stimulation‐induced signal changes in the human primary visual cortex
Authors: Menon Ravi S. , Ogawa Seiji , Tank David W. , Uǧurbil Kǎmil 
Published: March 2007

AbstractMulti‐echo measurements of photic stimulation‐induced signal changes in human visual cortex were made at 4 Tesla in order to quantify the nature of the signal change and its vascular origin, and to determine the optimum echo time for detection of the changes. Utilizing high resolution images, two distinct regions (ascribed to be microvasculature and visible venous vessels) were identified as giving rise to the signal increase. The fractional signal changes in gray matter areas depended linearly on echo time (TE) in the range of 10 to 60 ms and extrapolated to virtually zero for TE = 0, indicating that in‐flow effects secondary to stimulation‐induced blood flow increases were negligible in our functional imaging studies; instead, signal change due to photic stimulation originated from the increase in the apparent transverse relaxation rate, 1/T2*. This decrease in (1/T2*, brought about by the alterations in hemodynamic parameters, was 1.3 ± 0.4 s−1 for gray matter and 3.0 ± 0.7 s−1 (averaged over 10 individuals) for venous vessels visible in the images. The optimum choice of echo time was found to be TE ≥ T2*.
Dynamic 13C−1H nuclear polarization of lipid methylene resonances applied to broadband proton‐decoupled in vivo13C MR spectroscopy of human breast and calf tissue
Authors: Ende Gabriele , Bachert Peter 
Published: March 2007

AbstractDynamic nuclear polarization of the coupled 13C−lH spin system was studied for optimizing the signal‐to‐noise ratio of in vivo 13C MR spectra. In particular, the truncated driven and transient nuclear Overhauser effect (NOE) of the proton‐decoupled 13C resonances from methylene carbons in vegetable oil and in human calf tissue was observed. Maximum in vivo NOE enhancements n = 1.5 and 0.9 were found, respectively. Theoretical fits to the data yield 13C−1 cross‐relaxation times in the order of 0.6 s. Significant signal enhancement over the whole in vivo 13C chemical shift range is obtained with minimum expense utilizing the NOE of the dipolar coupled 13C−1 spin system in addition to proton‐decoupling. NOE‐enhanced proton‐decoupled in vivo 13C MR spectra were acquired within 17 min in volunteer examinations from the human breast and the calf. These spectra show well‐resolved resonances of carbons in lipids and several other cellular compounds.
Cylindrical coils near self‐resonance
Authors: Harpen Michael D. 
Published: March 2007

AbstractWe present a model of birdcage resonator operation when the size of the resonator approaches a quarter wave length resulting in significant phase shifts along the current conducting elements. In the model resonators are treated as generalized trainsmission lines. Line termination determines whether the resonator is of the low pass or high pass type. The model correctly describes the dependence of resonant frequency on resonant mode number as well as the distribution of current along the length of the resonator.
A new T2*‐weighting technique for magnetic resonance imaging
Authors: Hu Xiaoping , Kim Seong‐Gi 
Published: March 2007

AbstractThis paper describes a method that prepares the longitudinal magnetization with T2* weighting for subsequent acquisition. The main advantage of our technique is its insensitivity to static: field inhomogeneity. We have combined this approach with, an ultrafast gradient‐echo (Turbo‐FLASH) sequence and conducted experiments on phantoms and volunteers to demonstrate its capability and utility. With such a technique a T2*‐weighted image can be generated in less than a second. In the paper, the detail of the technique and experimental results are presented.
Evaluation of a nitroxyl fatty acid as liver contrast agent for magnetic resonance imaging
Authors: Gallez Bernard , Debuyst René , Demeure Roger , Dejehet Fernand , Grandin Cécile , Van Beers Bernard , Taper Henryk , Pringot Jacques , Dumont Pierre 
Published: March 2007

AbstractIn this study, we report the synthesis and the evaluation as MRI contrast agent of a new compound (nitroxyl fatty acid, NFA), where a pyrrolidinoxyl radical (3‐carboxy‐proxyl, PCA) is linked to a fatty acid moiety. Fatty acids were selected as vector because they present a high affinity for the liver, their efficient cellular uptake being the result of a specific interaction with a transmembrane transporter (liver plasma membrane‐fatty acid binding protein). The uptake of 3H‐oleic acid is inhibited after the injection of 1 mmol/kg of NFA, suggesting that INFA recognizes the same transmembrane transporter as the natural fatty acids. The higher relaxivity R1 of NFA in albumin solutions, compared with PCA, was explained by the immobilization of the nitroxyl radical in the protein. MR imaging was performed using T1‐weighted images on mice in order to compare the contrast effect obtained after the injection of 1 mmol/kg of radical. The % signal enhancement in the liver 5 min after intravenous injection was 49 ± 4 and 14 ± 5 for NFA and PCA, respectively. NFA allowed a better delimitation of some necrotic tumors (Novikoff hepatocarcinoma) due to its preferential uptake by the nontumorous tissue.
Ultrafast interleaved gradient‐echo‐planar imaging on a standard scanner
Authors: McKinnon G. C. 
Published: March 2007

AbstractUltra‐fast imaging traditionally implies either echo‐planar imaging on specially developed gradient systems, or very short repetition time gradient‐echo imaging on standard magnetic resonance imaging scanners. An alternative strategy for very fast imaging with conventional whole‐body scanners is discussed here. The technique is a hybrid, whereby the advantages of gradient‐echo imaging and echo‐planar imaging are combined. It is here denoted interleaved gradient‐echo‐planar imaging. It is not a single specific measurement sequence, but rather a continuum of sequences whereby multiple excitations with multiple gradient‐echos are employed. The power of this fast imaging approach is that one has much more flexibility toward the optimization of the measurement sequence with respect to imaging time, T2 relaxation, gradient power, resolution, image distortion, and signal‐to‐noise ratio. In vlvo human heart images, acquired in 110 ms, and with a resolution of 2.5 mm, have been obtained with a standard whole‐body scanner.
In vivo fluorine‐19 magnetic resonance spectroscopy of cerebral halothane in postoperative patients: Preliminary results
Authors: Menon D. K. , Lockwood G. G. , Peden C. J. , Cox I. J. , Sargentoni J. , Bell J. D. , Coutts G. A. , Whitwam J. G. 
Published: March 2007

AbstractThis study reports the use of 19F MRS to study halothane in the brain of eight patients recovering from halothane anesthesia of short duration. Resonances attributable to halothane were observed up to 90 min after withdrawal of the anesthetic agent. The signal‐to‐noise ratio for an unlocalized spectrum acquired using a 6 cm surface coil was typically 20 with data collection times of 2 min. In seven patients a single resonance was seen with a mean (±SD) chemical shift of +43.3 (±1.8) ppm, referenced to NaF at 0 ppm. This resonance exhibited a T1 value of between 0.5 and 1 s, and a T2* (estimated from the linewidth of the resonance) between 3.5 and 10 ms. In one patient two resonances were observed with chemical shifts of +38 and +41 ppm. Because we cannot exclude the possibility that this was due to field inhomogeneity, the significance of the last finding is uncertain. However, phantom studies show that the chemical shift of halothane in different environments (such as water, olive oil, methanol, and lecithin) can vary to an extent that accounts for the two resonances seen in our patient. These results demonstrate the feasibility of in vivo 19F MRS studies of fluorinated volatile agents in humans. The potential for clinical 19F MRS of fluorinated anesthetics is discussed.
Flow compensation in MRI using a phase‐corrected real reconstruction
Authors: Riek Jonathan K. , Totterman Saara M. , Tekalp A. Murat , Smith Warren E. , Kwok Edmund 
Published: March 2007

AbstractFlow‐ and motion‐related artifacts are problematic in clinical MR imaging. In this paper we discuss the utility of a phase‐corrected real reconstruction to reduce flow artifacts. This techinique is particularly useful when flow‐compensation pulse sequences may not be possible, such as when a very short echo delay or small field‐of‐view is desired. We will demonstrate that the phase‐corrected real reconstruction provides superior results to the magnitude reconstruction either used alone or in conjunction with existing flow‐compensation techniques.
Spatially selective RF pulses and the effects of digitization on their performance
Authors: Slotboom J. , Creyghton J. H. N. , Korbee D. , Mehlkopf A. F. , Bovée W. M. M. J. 
Published: March 2007

AbstractSpectrometers make use of D/A converters to generate RF and gradient shapes. This paper examines by exact simulations the time and amplitude digitization effects, inherent to the use of D/A converters, on the performance of amplitude modulated (AM) frequency selective RF pulses. By making use of Fourier theory and the small tip angle approximation, an approximate model of these effects on the magnetization slice profiles is derived and verified for several pulse types by computer simulations. This approximate model will be used to derive requirements for D/A converters with respect to spatial localization. The dynamics of the spin system allows pulse width modulation (PWM) as an alternative to AM for pulse envelope encoding. The effects of PWM on the slice profile are examined and compared with conventional AM pulses. It is shown by simulation and measurement that adiabatic PWM pulses can be found. In contrast to AM modulated adiabatic pulses, adiabatic PWM pulses have side bands with the same slice quality as the main slice and might therefore be useful as multislice selective pulses.
Algorithms for improving calculated streamlines in 3‐D phase contrast angiography
Authors: Buonocore Michael H. 
Published: March 2007

AbstractStreamline display is a unique alternative to cross‐sectional slice or projection display, because streamlines more clearly show the patterns of blood flow within the vessel. Flow patterns associated with atherosclerosis, such as streamline separation and recirculation, can be quickly identified with this display. Streamlines can be calculated using velocity data obtained from 3‐D phase contrast angiographic pulse sequences. However, these streamlines often pass through the wall of vessel or show intraluminal sources and sinks of blood. The author has developed iterative least squares algorithms to improve the realism of streamlines. The velocity data is modified so that the resulting streamlines do not pass through the vessel wall and there are no intraluminal sources or sinks. He has applied the algorithms to velocity data obtained from a flow phantom and the carotid arteries of normal volunteers. Streamlines derived from the processed velocity fields are more realistic and provide more precise flow quantitation.
Estimation of bloch model MT spin system parameters from Z‐spectral data
Authors: Holt R. W. , Duerk J. L. , Hua J. , Hurst Gregoly C. 
Published: March 2007

AbstractPrevious studies have described magnetization transfer (MT) Z‐spectra in terms of a two‐pool Bloch model, with six spin‐system parameters KA, F, T1A, T1B, and T2B. By simulation, we show that a process including nonlinear constrained optimization can be used to accurately and uniquely estimate spin‐system parameters from MT 2‐spectra prepared by continuous wave (CW) RF irradiation. Experiments producing Z‐spectra by pulsed RF irradiation give substantially different magnetization values, relative to MT acquisitions obtained by CW RF irradiation, at small offset frequencies, with a consequence that only T2B can be uniquely determined. However, several equalities and bounds involving four of the other parameters (KA, F, T1A, T1B) are derived, which are applicable to pulsed data. These relationships allow calculation of “free pool” magnetization corresponding to complete saturation of the restricted pool, without requiring that this complete saturation be experimentally achieved. MT experimental data from pulsed RF irradiation on boiled egg albumin, obtained using a clinical whole‐body MRI system, are analyzed using an optimization algorithm and the derived expressions.
In Vivo and in vitro EPR oximetry with fusinite: A new coal‐derived, particulate EPR probe
Authors: Vahidi N. , Clarkson R. B. , Liu K. J. , Norby S. W. , Wu M. , Swartz H. M. 
Published: March 2007

AbstractThe peak‐to‐peak line width (LW) of the first derivative electron spin resonance (EPR) spectrum of the coal maceral fusinite is reversibly broadened by O2. The extent of broadening per unit of partial pressure of oxygen (pO2) is unusually large, exceeding that of nitroxides by almost two orders of magnitude. This paramagnetic properly of fusinite, combined with its very stable physicochemical properties and low toxicity, is shown to be of utility in the measurement of pO2 in vitro and in vivo. Fusinite particles are endocytosed by Chinese hamster ovary (CHO) cells in vitro; this is useful for intracellular O2 measurements with commercially available EPR spectrometers operating at 9.1‐9.3 GHz. For measurement of oxygen in vivo using low frequency EPR (1.l‐1.3 GHr), fusinite provides a sensitive and persistent means to measure pop in tissues. Particles implanted into the gastrocnemius muscle of NJ mice remained interstitially in the same position for months with undiminished sensitivity to pO2 and no specific toxic effects.
MRA studies of arterial stenosis: Improvements by diastolic acquisition
Authors: Saloner David , Selby Kathy , Anderson Charles M. 
Published: March 2007

AbstractCardiac‐phase‐specific data acquisition is used to reduce signal loss in MR Angiography resulting from disturbed flow. RF pulses are delivered continuously throughout the cardiac cycle, but incrementation of phase‐encoding gradients and data storage are enabled only during the chosen part of the cycle. Studies in a stenotic pulsatile flow phantom demonstrate that poststenotic signal loss is primarily determined by the mean flow velocity, and is not appreciably affected by acceleration or deceleration of the mean flow rate. The signal loss is least in diastole. In vivo studies in patients with carotid artery disease show that data acquisition in diastole reduces the apparent degree and extent of carotid bifurcation stenosis and provides a crisper definition of the vascular lumen. The additional time required for cardiac‐phase‐specific acquisition can be reduced by gating only the lower‐order phase‐encoding lines while retaining acceptable image quality.
The presence of cytoplasmic lipid droplets is not sufficient to account for neutral lipid signals in the 1H spectra of neutrophils
Authors: May G. L. , Sztelma K. , Sorrell T. C. 
Published: March 2007

AbstractStimulation of human peripheral blood neutrophils with lipopolysaccharide (LPS), arachidonic acid (AA) and oleic acid (OA) resulted in significant increases in cytoplasmic lipid droplets. This phenomenon was also observed in enucleated and degranulated cytoplasts prepared from neutrophils stimulated with LPS. In contrast, only LPS and high concentrations of OA (10 μM) produced an increase in the lipid intensities of the MR spectra of neutrophils as determined by COSY cross peak volume measurements. Lipid intensities in cells stimulated with OA (2.5 μM) and AA (2.5 μM) and phorbol myristate acetate (20 nM) were not elevated. LPS stimulation of resting cytoplasts resulted in increased lipid droplets but not MR lipid intensities. These data suggest that while cytoplasmic lipid droplets may correlate with MR lipid intensity under some circumstances, their presence is not sufficient to account for increased neutral lipid signals.
Comparisons of ATP turnover in human muscle during ischemic and aerobic exercise using 31P magnetic resonance spectroscopy
Authors: Kemp G. J. , Thompson C. H. , Barnes P. R. J. , Radda G. K. 
Published: March 2007

AbstractTo investigate human muscle bioenergetics quantitatively in vivo, we used 31P magnetic resonance spectroscopy to study the flexor digitorum superficialis of four adult males during dynamic ischemic and aerobic exercise at 0.50–1.00 W and during recovery from aerobic exercise. During exercise, changes in pH and [PCr] were larger at higher power, but in aerobic exercise neither end‐exercise [ADP] nor the initial postexercise PCr resynthesis rate altered with power. In ischemic exercise we estimated total ATP synthesis from the rates of PCr depletion and glycogenolysis (inferred using an analysis of proton buffering); this was linear with power output. In aerobic exercise, again we estimated ATP synthesis rates due to phosphocreatine hydrolysis and glycogenolysis (incorporating a correction for proton efflux) and also estimated oxidative ATP synthesis by difference, using the total ATP turnover rate established during ischemic exercise. We conclude that in early exercise oxidative ATP synthesis was small, increasing by the end of exercise to a value close (as predicted) to the initial postexercise rate of PCr resynthesis. Furthermore, a plausible estimate of proton efflux during aerobic exercise can be inferred from the pH‐dependence of proton efflux in recovery.
Phantom studies simulating the impact of trabecular structure on marrow relaxation time, T2′
Authors: Engelke Klaus , Majumdar S. , Genant H. K. 
Published: March 2007

AbstractPhantom studies were conducted to investigate the impact of trabecular structure on the T2′ signal measured by MRI. For a separation of density from structural effects, several phantoms were built. They consisted of parallel polyethylene strings arranged in a variety of different patterns to simulate (a) a constant uniform trabecular distribution with increasing trabecular thickness and (b) different structures with identical overall trabecular density. An asymmetric spin echo sequence was used to determine the apparent relaxation time T2′. Changes in T2′ are induced by susceptibility differences between the polyethylene strings simulating trabeculae and Gd‐TPA doped saline simulating bone marrow. The results showed an increasing T2′ decay rate with (a) decreasing spacing while the string density was constant and (b) with increasing string density while the string arrangement was constant. The results demonstrate that the T2′ signal is affected not only by density but also by spatial distribution. However, the results also indicate that a separation of the two effects is not possible from a T2′ measurement alone, but that e.g., a matching CT slice that would provide purely density information is additionally needed. Theoretical simulations confirmed these results.
Gd‐DOTA as a gastrointestinal contrast agent for gastric emptying measurements with MRI
Authors: Schwizer W. , Fraser R. , Maecke H. , Siebold K. , Funck R. , Fried M. 
Published: March 2007

AbstractCurrent MR meal markers may interfere with gastric motility and secretion restricting the use of MRI in the measurement of gastric physiology. We therefore evaluated Gd‐DOTA as a liquid phase marker, in vitro by determining dissociation, and adherence to the solids, and in vivo by simultaneous MRI (0.35 T scanner, multiple T1‐weighted sections of the upper abdomen) and double indicator (perfusion marker PEG 4000, meal marker 99mTc‐DTPA) measurements of emptying and secretion, following ingestion of 500 ml 10% glucose. In vitro Gd‐DOTA was stable at a pH > 2 with < 2% dissociation at 24 h during incubation with HCI. Dissociation during incubation with HCI was linearly dependent on H+ concentration (0.77 < pH < 2.02). Less Gd‐DOTA was absorbed onto the solid phase than 99mTc‐DTPA (25% cf 36%). in vivo Gd‐DOTA marked gastric contents provided strong positive contrast. Similar emptying curves were observed with both MRI and double‐indicator techniques (r = 0.987, P < 0.001). Gd‐DOTA has the potential to be a useful liquid phase contrast agent in MR studies on gastric function.