bluuebunny/crossref_metadata_2025_split huggingface dataset:
Blood Clearance of Dextran Magnetite Particles Determined by a noninvasive in vivo ESR method
Authors: Iannone A. , Magin R. L. , Walczak T. , Federico M. , Swartz H. M. , Tomasi A. , Vannini V. 
Published: March 2007

AbstractDextran magnetite (DM) is a potential MR contrast agent with superparmagnetic properties. Its fast clearance from the blood and selective uptake by tissue macrophages provide advantages for imaging tumors in the liver and spleen. DM consists of a suspension of solid particles with a wide distribution of sizes, In this study we have used ESR spectroscopy to determine the blood clearance of DM injected iv mice. The spectra are obtained on living animals by inserting the tail of a mice into the waveguide cavity of the ESR spectrometer and recording the ESR spectrum continously. This procedure allows the direct measurement of the plasma clearance of DM from individual animals, without blood sampling. We applied this method to study the clearance of suspensions of DM particles with different averge sizes. © 1991 Academic Press, Inc.
Determination of cytosolic ADP and AMP concentrations and the free energy of ATP hydrolysis in human muscle and brain tissues with 31P NMR spectroscopy
Authors: Roth K. , Weiner M. W. 
Published: March 2007

AbstractBased on experimentally determined concentrations of PCr, Pi, ATP, and H+, the ADP and AMP concentrations and the free energy for the ATP hydrolysis in normal human brain and muscle were calculated assuming that the creatine kinase‐ and the myokinase‐catalyzed reactions were in equilibrium, accounting for changes in pH and free Mg2+ ion concentration. © 1991 Academic Press, Inc.
In vivo1H and 31P NMR spectroscopy of the developing rat brain
Authors: Hida Kazutoshi , Kwee Ingrid L. , Nakada Tsutomu 
Published: March 2007

AbstractThe biochemical changes associated with brain maturation during the first 28 days postnatal were investigated utilizing proton and phosphorus‐31 nuclear magnetic resonance spectroscopy in rat pups in vivo. Phosphocreatine was found to increase linearly during this period of development. Phosphomonoester was high at birth, peaked around the 10th day postnatal, and declined thereafter. N‐Acetyl‐aspartate was low at birth, increased in an approximately linear fashion, and reached adult levels by about Day 28 postnatal. Choline was high at birth and declined thereafter. Taurine, a sulfur amino acid abundant in fetal brain, was also present in high levels on the first day postnatal. © 1992 Academic Press, Inc.
NMR relaxation times in acute myocardial infarction: Relative influence of changes in tissue water and fat content
Authors: Scholz Thomas D. , Martins James B. , Skorton David J. 
Published: March 2007

AbstractTissue changes known to occur with acute myocardial infarction include increases in tissue water and lipid content. We sought to evaluate the relative contribution of alterations in tissue water and fat content to the changes of Tl and T2 relaxation times with infarction. Nine mongrel dogs underwent coronary artery occlusion for 6–12 h. T1 and T2 at 20 MHz and tissue water and fat content of normal and infarcted tissue were measured. Tissue water content, T1, and T2 were significantly greater in infarcted myocardium compared to normal (P < 0.05). Tissue fat content, while not significantly different, increased linearly in infarcted samples as a function of duration of ischemia (r = 0.77). Despite this increase in fat content, only tissue water content was significantly linearly related to T1 (r = 0.97) and T2 (r = 0.91). Increases in T1 and T2 of infarcted tissue appeared to be most significantly influenced by changes in tissue water content. While total tissue fat content increased with duration of ischemia, it did not appear to significantly alter T1 or T2. © 1992 Academic Press, Inc.
Fast angiography using selective inversion recovery
Authors: Wang Samuel J. , Nishimura Dwight G. , Macovski Albert 
Published: March 2007

AbstractWe have developed an enhancement of selective inversion recovery that allows us to obtain high‐resolution angiograms in reduced Scan time. By applying several read pulses following each tagging inversion pulse, we can obtain several phase encodes in each cardiac cycle, thereby reducing the total scan time required for a complete image. Using this technique, high‐resolution angiograms can be obtained in as little as 15 s. Because the phase encodes are collected in short bursts separated by long pauses, care must be taken to maintain uniform signal weighting across phase‐encoding views and avoid ghosting. We use an increasing flip‐angle sequence to equalize signal level weighting across the readouts. The phase encodes are collected in a special order to minimize ghosting. A postprocessing technique is used to further reduce signal nonuniformity between phase encodes. This fast angiography technique can significantly reduce artifacts due to patient motion during scanning and is especially useful for imaging vasculature in regions of the body where respiratory motion is a problem. © 1992 Academic Press, Inc.
1H NMR study of cortex neurons and cerebellar granule cells on microcarriers and their PCA extracts: Lactate production under hypoxia
Authors: Sonnewald U. , Petersen S. B. , Krane J. , Westergaard N. , Schousboe A. 
Published: March 2007

AbstractLactate production of 6‐day‐old cerebral cortex neurons and 7‐day‐old cerebellar granule cells from mouse brain attached to cytodex 3 microcarriers was studied as a function of time, under hypoxic conditions using 1H NMR. Perchloric acid extracts of both cell types were prepared and 1H NMR spectra showed compounds characteristic for these neurons. In particular the granule cell extracts showed a large amount of glutamate as expected from biochemical experiments, whereas the cortex neurons showed a large amount of 4‐ aminobutyric acid. © 1992 Academic Press, Inc.
Respiratory kinematics of the upper abdominal organs: A quantitative study
Authors: Korin Hope W. , Ehman Richard L. , Riederer Stephen J. , Felmlee Joel P. , Grimm Roger C. 
Published: March 2007

AbstractDespite the fact that respiratory motion is a major factor limiting the image quality of MR examinations in the upper abdomen, little quantitative information is available about the kinematics of visceral motion during respiration. The objective of this study was to obtain a measure of the relative longitudinal and transverse displacements of the upper abdominal organs during breathing using an MR line scan technique. © 1992 Academic Press, Inc.
Permeability of liposomal membranes to water: Results from the magnetic field dependence of T1 of solvent protons in suspensions of vesicles with entrapped paramagnetic ions
Authors: Koenig Seymour H. , Ahkong Quet F. , Brown Rodney D. , Lafleur Michael , Spiller Marga , Unger Evan , Tilcock Colin 
Published: March 2007

AbstractThe diffusive permeability to water molecules, Pd, of lipid vesicles with entrapped paramagnetic solute ions can be determined rapidly from analysis of the magnetic field dependence (nuclear magnetic relaxation dispersion, or NMRD profile) of T1 of exterior solvent water protons. Such data yield τ the mean lifetime of solvent molecules inside the vesicles, from τ = (fTlpara) – T1ves, where f is the volume fraction of entrapped water, T1Para is the observed T1 corrected for buffer background, and T1Ves is the relaxation time of water protons in the entrapped solution. For small spherical unilamellar vesicles of inner radius R, Pd = R/3τ. f can be obtained accurately from knowledge of both the concentration of Gd(DTPA)2− in the solution in which the vesicles were formed and the average concentration of ions in the final sample. At low temperatures, in the limit of slow exchange, T1Para becomes independent of field and τ = f T1Para; the observation of a field independent profile is a control that confirms that no paramagnetic material is external to the vesicles. We have measured T1Para, using a field‐cycling relaxometer, for suspensions of POPC (1‐palmitoyl‐2‐oleoyl‐lecithin) vesicles with 100–500 mM entrapped Gd(DTPA)2− and membrane concentrations of cholesterol ranging from 0 to 40 mol %. These profiles, which span the field range 0.01–50 MHz proton Larmor frequency, were taken at 5, 15, 25, and 35°C. Concentrations of Gd(DTPA)2− were determined independently by both ICP analyses and NMRD methods. Values for Pd for vesicles with 100 mM Gd(DTPA)2− and outer diameters 100 nm ± 20%, as determined by quasielastic light scattering, are 63, 47, 24, 16, and 8.7 × 10−4cm s−1, at 25°C, for cholesterol concentrations of 0, 10, 20, 30, and 40%, respectively. The corresponding activation enthalpies are 14, 14, 14, 17, and 17 kcal/M. Comparison with 2H NMR studies of deuterated POPC vesicles with no cholesterol at 20°C, and with 10% at 40°C, which yielded the same order parameter for the palmitoyl acyl chains, gives no indication of a correlation between order parameter and permeability.
A double‐tuned probe for metabolic NMR studies
Authors: Najim Elhadi , Grivet Jean‐Philippe 
Published: March 2007

AbstractA double‐tuned single coil probe for high field metabolic NMR studies has been designed and tested. The resonant coil is a single‐turn of copper foil wound on a quartz cylinder. It is fed by a short length of parallel strip line made of the same material; the feeder is also used as a tuning capacitance. Electrical parameters (quality factors, efficiencies at proton and carbon frequencies) and magnetic resonance data (90° pulse lengths, minimum decoupler power) for lossy samples have been measured. The probe allows for the optimal use of the limited high homogeneity region of a vertical magnet. It shows good sensitivity and efficient decoupling. © 1992 Academic Press, Inc.
High‐Resolution 1H NMR spectroscopy studies of extracts of human cerebral neoplasms
Authors: Peeling James , Sutherland Garnette 
Published: March 2007

AbstractHigh‐resolution 1H NMR spectroscopy has been used to measure the concentrations of metabolites (alanine, N‐acetylaspartate, γ‐aminobutyric acid, glutamate, glutamine, aspartate, taurine, glycine, succinate, creatine, cholines, inositol, and glucose) in perchloric acid extracts of human epileptic cortex and brain tumors. All tissue was obtained by surgical biopsy, excised before thermal coagulation, and immediately frozen in liquid nitrogen. Lower levels of N‐acetylaspartate and γ‐aminobutyric acid and a shift in the glutamate/glutamine ratio toward glutamine in the tumors reflect neuronal loss. Abnormal glucose metabolism (aerobic glycolysis) in the tumors gives decreased levels of succinate, glutamate, aspartate, glutamine, and creatine and generally increased concentrations of glycine and alanine. Differences in metabolite concentrations that may be of use in differential tumor diagnosis include lower creatine and inositol in meningiomas than in astrocytomas. Lower taurine differentiates benign from malignant astrocytomas. Malignant astrocytomas and metastatic tumors are more regionally heterogeneous than meningiomas or benign astrocytomas. Mannitol, administered perioperatively to all patients from whom tissue was obtained, was observed only in the spectra of extracts of tissue from tumors which enhanced on computerized tomographic imaging. © 1992 Academic Press, Inc.
MR microimaging of articular cartilage and contrast enhancement by manganese ions
Authors: Kusaka Y. , Gründer W. , Rumpel H. , Dannhauer K.‐H. , Gersonde K. 
Published: March 2007

AbstractSaline solutions of manganese ions (Mn2+) were used as articular contrast agents in magnetic resonance microscopy (9.4 T) of cartilage of chicken femoral condyles and pig temporomandibular joints. The diffusion of Mn2+ from the articular surface into the cartilage matrix led to a strong contrast enhancement in the cartilage. The combination of the high spatial resolution and the contrast enhancement allowed the visualization of fine structures (tissue types) in the cartilage, which correlate with the tissue zones in histological sections stained with cationic dyes. We assume that the electrostatic interactions between the negatively charged groups of the proteoglycans and Mn2+ are most important for the mechanism of contrast enhancement. Hence, the different signal intensities of the various zones of cartilage indicate differences in density of proteoglycans. The intraarticular injection of the cationic contrast agent could improve the possibility of an early diagnosis of cartilage dysfunction and degeneration. © 1992 Academic Press, Inc.
Magnetization transfer effects in multislice RARE sequences
Authors: Melki P. S. , Mulkern R. V. 
Published: March 2007

AbstractMagnetization transfer effects are demonstrated to be significant in determining the signal intensity from brain tissues on images acquired with multislice rapid acquisition relaxation enhanced (RARE) sequences. We report studies designed to determine how the signal intensities vary with slice number or, equivalently, off‐resonance power deposition. The results obtained in fat, gray matter, and white matter are similar in form to those reported in kidney tissues during classic magnetization transfer experiments (J. Eng, T. L. Ceckler, and R. S. Balaban, Magn. Reson. Med. 17,304 (1991)). Of clinical significance to RARE practitioners is the increase of contrast‐to‐noise ratios between gray and white matter on proton density‐weighted images with increasing slice number. © 1992 Academic Press, Inc.
Magnetically coupled paramagnetic relaxation agents
Authors: Lester Cathy Coolbaugh , Bryant Robert G. 
Published: March 2007

AbstractMeasurements of the spin‐lattice relaxation rates of water protons made over a wide frequency range have demonstrated that the effects of paramagnetic relaxation agents may be considerably enhanced when the paramagnetic center is incorporated into a compact structure macromolecule such as a protein that is rotationally constrained. The immobilization of the macromolecule profoundly changes the nature of the magnetic field dependence of the relaxation rate for both the diamagnetic and the paramagnetic samples. The immobilization also amplifies the effect of the paramagnetic center as a water‐proton relaxation agent. The direct exchange of labile water molecules or protons is not a requirement for the high efficiency of this class of magnetic relaxation agents. © 1992 Academic Press, Inc.
Intravascular (catheter) NMR receiver probe: Preliminary design analysis and application to canine iliofemoral imaging
Authors: Hurst Gregory C. , Hua Jianmin , Duerk Jeffrey L. , Cohen Alan M. 
Published: March 2007

AbstractThis investigation explores the feasibility of a catheter‐based receiver probe for NMR study of arterial walls. Simulations and phantom experiments demonstrate the spatial response of several “inside‐out” probe coil designs, including loop, “birdcage,” “multipole,” “center return,” and opposed solenoids. For a target defined by an annulus in a plane perpendicular to B0, the opposed solenoid design provides substantially superior homogeneity to other designs considered. Canine iliofemoral artery images were acquired using a catheter probe in a whole‐body, 1.5‐T clinical imaging system. In situ (cadaver) images acquired with TE 70, TR 2400,2‐mm slice thickness, and 78 × 78‐μm in‐plane voxel size in 10‐min acquisition times show vessel wall structures identified as intima, internal elastic lamina, media, and adventitia. In vivo images from similar acquisition conditions are much more poorly resolved, presumably due to motion, despite the use of cardiac gating and gradient moment nulling, so the feasibility of obtaining high‐resolution in vivo MR images of the arterial wall remains in doubt. © 1992 Academic Press, Inc.
In vivo17O NMR study of rat brain during 17O2 inhalation
Authors: Fiat D. , Ligeti L. , Lyon R. C. , Ruttner Z. , Pekar J. , Moonen C. T. W. , McLaughlin A. C. 
Published: March 2007

AbstractIn vivo 17O NMR has been used to monitor the H2 17O concentration in rat brain during inhalation of 17O2. The results are discussed in terms of oxygen consumption in the brain and recirculation into the brain of H2 17O produced in other organs. © 1992 Academic Press, Inc.
Direct imaging of magnetic field gradients by group spin‐echoselection
Authors: Posse Stefan 
Published: March 2007

AbstractA new image processing method for single‐echo gradient echo imaging is presented which extracts local phase gradient information by k‐space filtering instead of by phased reconstruction and spatial differentiation. It is shown that localphase gradient directions and semiquantitative local phase gradient magnitudes can be directly measured, even in regions where phased image reconstruction suffers from multiple phase foldovers due to strong phase modulations. The directional information thus obtained can be used as a reference to identify and correct phase modulation foldovers i phase maps which may be computed from the same raw data. The method is applied here to measure static magnetic field gradients and illustrates fundamental k‐space signal properties of gradient echo imaging. Based on this concept, image artifacts caused by conventional strong k‐space filtering in gradient echo imaging are discussed.
Concurrent quantification of tissue metabolism and blood flow via 2h/31P NMR in vivo. i. assessment of absolute metabolite quantification
Authors: Song Sheng‐kwei , Hotchkiss Richard S. , Ackerman Joseph J. H. 
Published: March 2007

AbstractIn a series of three papers, we demonstrate and validate an approach for concurrent absolute quantification in situ of blood flow and energy metabolism with a modification of the NMR methodfor absolute concentration determination put forth by Thulborn and Ackerman [J. Magn. Reson. 55, 357 (1983)] and later expanded upon by Tofts and Wray. In this first paper of the series, we briefly review the theoretical basis for the concentration measurement and present, for the first time, a successful paired validation of metabolite quantification via 31P surface‐coil NMR through corroborative in vitro enzymatic assays. The paired radiolabeled microsphere validation of blood flow measurement via 2H surface‐coil NMR employing D2O as a freely diffusible tracer and the concurrent determination of blood flow and energy metabolism in a septic rat model are presented in the accompanying second and third paper to completethe series. In this article aclassical RF tank circuit is employed to describe the effect of conductive sample loading on the NMR receiver by considering its apparent series resistance. It is shown in aneasily visualized generalizable manner that the effect of sample loading on the observed NMR signal intensity can be accounted for quantitatively by monitoring changes in 90° pulse width at constant power at a fixed reference point, i.e., SSample= Sphantom(PW90pphantom/PW90sample). In a series of paired experiments the absolute concentrations of high energy phosphates obtained from resting rat leg muscle (n = 4) in situ (NMR) and in vitro (enzymatic) were determined as follows: [PCr]NMR = 17.2 ± 0.8 SD, [PCT]enzymatic, = 17.3 ± 2 SD, [ATP]NMR = 5.1 ± 0.8 SD, [ATP]enzymatic, = 5.0 ± 0.2 SD mmol/kg tissue wet wt. Results of these two independent methods of concentration determination were not statistically different (P = 0.94 and P = 0.74 respectively) and serve to rigorously validate the Thulborn approach for absolute quantification of phosphorous metabolites in situ via NMR. Furthermore, these results strongly suggest that ATP and PCr in resting rat leg muscle under normal physiologic conditions are 100% NMR visible. The free cytosolic [ADP]NMR was estimated from the creatine kinase reaction equilibrium expression to be 0.022 ± 0.003 SD mmol/kg tissue wet wt.
Proton NMR studies on ischemic rat brain tissue
Authors: Iwama T. , Yamada H. , Andoh T. , Sakai N. , Era S. , Sogami M. , Kuwata K. , Wataris H. 
Published: March 2007

AbstractThe spin‐lattice relaxation time (T1) of water protons and the cross‐relaxation time (Tis) between irradiated protein protons and observed water protons were measured in order to study water‐macromolecular interactions in ischemic rat brain tissues. Tissueswere obtained by bilateral common carotid artery occlusion from stroke‐prone spontaneously hypertensive rats. Water, Na, and K contents were measured in ischemic brain tissue at the same time. Water and Na content increased while the T1value and K content decreased following ischemic insults. The T1value did not change until 180 min after ischemia had been induced. Changes in the Tlsvalue occurred earlier than changes observed for the T1value, water, and electrolyte contents. Results indicate that the value of Tis, may be useful for detecting cerebral ischemia and that the physical structure of water‐macromolecular interaction may be altered soon after ischemic onset in brain tissue.
1H spectroscopic imaging of rat brain at 7 tesla
Authors: Fernandez E. J. , Maudsley A. A. , Higuchi T. , Weiner M. W. 
Published: March 2007

Abstract1H magnetic resonance spectroscopic imaging has been used to obtain metabolite maps of the rat brain. The spin‐echo‐based technique has been evaluated with respect to water and lipid suppression and sensitivity. Metabolite maps were constructed for choline. creatine + phosphocreatine, amino acids, Nacetyl aspartate, and lactate. A spatial resolution of 3 × 3 mm (in plane) with 7‐mm‐thick slices was achieved routinely in 60‐min (16 × 16 phase encoding) acquisitions. For higher intensity resonances, metabolite maps could be constructed in as little as 10 min. Results from phantoms and from rats under normal and focal ischemia conditions are presented.
Comparison of in Vivo and in vitro Hahn T2 measurements in rat lung
Authors: Shioya Sumie , Kolem Heinrich , Ailion David C. , Goodrich K. Craig , Cutillo Antonio G. , Morris Alan H. , Durney Carl H. 
Published: March 2007

AbstractWe compared in vivo and in vitro Hahn echo T2 measurements in rat lungs in both imaging and nonimaging modes. All measurements could be characterized by multiexponential functions consisting of either two or three exponentials. Essentially the same values of the time constants were observed for spontaneously breathing rats and for excised lungs. © 1991 Academic Press, Inc.
Quantitative MR in the diagnosis of multiple sclerosis
Authors: Haughton Victor M. , Yetkin F. Zerrin , Rao Stephen M. , Rimm Alfred A. , Fischer Mary E. , Papke R. Anne , Breger Robert K. , Khatri Bhupendra O. 
Published: March 2007

AbstractIn patients with multiple sclerosis (MS), the apparently uninvolved cerebral white matter between demyelinated plaques may have biochemical abnormalities. To what degree the changes in the white matter contribute to symptomatology in MS is unknown. In 39 patients with multiple sclerosis, and in 39 age‐matched nondiseased volunteers, T1 and T2 were calculated from spin‐echo images in four regions of apparently uninvolved white matter. In three of four white matter areas, the average T1 and T2 were significantly longer in the patients than in the controls. The T1 correlated with the disability, measured by the Kurtzke Extended Disability Status Scale, although the correlation was marginally significant. The results suggest that in patients with MS, white matter disease that is not visualized in MR as distinct foci of abnormal signal intensity may contribute to disease burden and disability.