bluuebunny/crossref_metadata_2025_split huggingface dataset:
Image reconstruction from Fourier domain data sampled along a zig‐zag trajectory
Authors: Yan Hong , Braun Michael 
Published: March 2007

AbstractWhen the conventional Fourier transform (FT) algorithm is applied to reconstruct a magnetic resonance (MR) image from data sampled along a zig‐zag trajectory in the Fourier space, the nonuniform sampling in the spatial frequency direction may give rise to artifacts. In this paper the nature of the artifacts is analyzed and an alternative reconstruction algorithm is developed to produce artifact‐free images. Methods for reducing noise level in the reconstructed image are discussed. Our approach is compared with another method based on the interlace sampling theorem. © 1991 Academic Press. Inc.
A general formalism for the manipulation of multiple‐echo data sets, and application to chemical shift editing
Authors: Webb A. G. , Hall L. D. 
Published: March 2007

AbstractA general data processing formalism is presented which can be applied to the signal intensities of successive echoes of a multiple‐echo data set in order to null those species for which the signal decay function is exponential. If asymmetric echo times are introduced into the multiple‐echo sequence then chemical shift images akin to those obtained from the magnitude Dixon method can be obtained in half the data acquisition time. © 1991 Academic Press. Inc.
Nonperturbing test for cytotoxicity in isolated cells and spheroids, using electron paramagnetic resonance
Authors: Dobrucki Jerzy W. , Sutherland Robert M. , Swartz Harold M. 
Published: March 2007

AbstractElectron paramagnetic resonance imaging (EPRI) and EPR spectroscopy of nitroxides have been applied to detect and quantify cytotoxic effects in mammalian cells in vitro Images depicting microscopic viable and nonviable areas in the same multicellular spheroid (a model of solid tumors) have been acquired prior to and following the treatment with an antitumor drug, Adriamycin. The loss of viability in the inner region of the viable rim was detected. Such mapping of the time‐course changes of the localization of viable and nonviable cells in the same intact biological object is not possible with routinely used methods to measure viability, such as histological examination. The experimental conditions required for high accuracy and sensitivity of the EPRI of spheroids have been evaluated and directions for further development of this approach are indicated. © 1991 Academic Press, Inc.
Comparative evaluation of two membrane‐based liposomal MRI contrast agents
Authors: Karlik Stephen , Florio Eugene , Grant Chris W. M. 
Published: March 2007

AbstractTwo phospholipids—one bearing a nitroxide free radical covalently attached to its polar headgroup, and the other bearing a similarly attached chelating agent with bound gadolinium—were compared in vivo as liposomal contrast agents for MR imaging. In each case the phospholipid contrast agent was incorporated into the membranes of sonicated unilamellar vesicles. The agent with bound gadolinium proved to be considerably more potent at highlighting regions of liposome biodistribution than did its spin‐labelled analogue. Injected intramuscularly into rats, the spin‐label liposomes produced local tissue contrast that persisted for 1 h; while under similar conditions, the liposomal gadolinium persisted for over 24 h. By comparison, water‐soluble, nonliposomal DTPA‐Gd3+ (dimeglumine), was rapidly cleared from the same intramuscular sites—appearing in kidney and bladder within 15 min of injection. When delivered intravenously, maximum effect from both liposomal agents was observed in liver and spleen within 1–2 h, although the spin‐label agent produced only marginal contrast. The concomitant use of fat suppression proved a valuable adjunct to liposomal contrast for imaging organs of the reticuloendothelial system. © 1991 Academic Press, Inc.
Simultaneous multinuclear magnetic resonance imaging and spectroscopy
Authors: Moore Gregory J. , Hrovat Mirko I. , González R. Gilberto 
Published: March 2007

AbstractA technique has been developed to perform simultaneous multinuclear magnetic resonance imaging and spatially localized spectroscopy. It is inherently superior in terms of time efficiency over current approaches which use sequential or interleaved methods. The pulse sequence uses a parallel excitation and acquisition scheme to acquire multislice proton images concurrently with phosphorus‐31 spectroscopic images. Because the phosphorus signal is necessarily collected in the presence of a gradient, an essential element of the technique is an algorithm to extract pure chemical‐shift information. © 1991 Academic Press, Inc.
In vivo NMR, biochemical, and histologic evaluation of alcohol‐induced fatty liver in rat and a comparison with CCl4 hepatotoxicity
Authors: Hazle John D. , Narayana Ponnada A. , Dunsford Harold A. 
Published: March 2007

AbstractMagnetic resonance imaging (MRI) and spectroscopy (MRS) were used to follow the time course of ethanol‐induced fatty liver in a group of 10 rats fed a diet containing 12% alcohol (ethanol) over a 5‐week period. The MR data consisted of T1‐weighted images, in vivo 1H spectra, and in vivo T1, relaxation measurements. Changes in short TR images as a result of fatty accumulation were noted only as a slight increase in liver intensity relative to surrounding muscle. A poorly correlated (r = 0.54) increase in water T1 with time was observed. No statistically significant changes in lipid T1 were found. MRS derived lipid content was compared with biochemically derived total lipids and histology. MRS determined liver lipids were found to increase linearly with time (r = 0.91). Biochemically derived lipid content also increased with prolonged exposure to ethanol (r = 0.96). The averages of MRS derived lipid content agreed well with the average changes in biochemically determined total lipid concentration. Histologic examination revealed slight to moderate changes in fatty accumulation with significant variation in the group at the end of the study. On an individual basis the MRS and histologic evaluation were highly correlated (r = 0.94). © 1991 Academic Press, Inc.
Dynamic changes in 13C NMR spectra of intact hearts under conditions of varied metabolite enrichment
Authors: Lewandowski E. Douglas , Hulbert Chrys 
Published: March 2007

AbstractDynamic changes in 13C NMR signal from enriched glutamate pools within hearts have been examined under varied conditions of metabolite pool size and fractional enrichment. Relative signal intensities of 13C‐enriched glutamate isotope isomers were similar within spectra from both intact hearts and corresponding in vitro samples. The parameters used to assess metabolic activity with 13C NMR proved independent of fractional enrichment and pool size. The data show the importance of acknowledging unlabeled, 13C NMR invisible metabolites. © 1991 Academic Press, Inc.
Sucrose polyester: A new oral contrast agent for MRI
Authors: Ballinger Ray , Magin Richard L. , Webb Andrew G. 
Published: March 2007

AbstractSucrose polyester (a dietary fat substitute) opacifies the entire gastrointestinal tract of the rat with oral administration in magnetic resonance imaging (MRI). These results suggest the potential use of this material as an oral contrast agent for human abdominal MRI studies. © 1991 Academic Press, Inc.
Applications of the intravoxel coherent motion technique to the central nervous system
Authors: Young I. R. , Doran M. D. , Hajnal J. V. 
Published: March 2007

AbstractPhase difference images, obtained by comparing data from motion‐sensitized and ‐unsensitized spin‐echo sequences, can be used to study intravoxel coherent motions. The resulting images, which have been routinely used to study fast flowing blood, may potentially yield information about perfused flows and bulk tissue motion. The likely limitations and potential of this technique applied to the central nervous system are reviewed with reference to parallel studies of intravoxel incoherent motion. © 1991 Academic Press, Inc.
Diffusion/microcirculation MRI in the rat brain
Authors: Macfall J. R. , Maki J. H. , Johnson G. A. , Hedlund L. , Benveniste H. , Copher G. 
Published: March 2007

AbstractThe CO2 fraction of an anesthetized rat's breathing mixture was changed (from 0 to 10%) to attempt to change the brain microcirculation and observe these changes in diffusion measurements of the neural tissue. Brain apparent diffusion coefficients were measured to be (0.71 ± 0.01) × 10−1 mm2/s before sacrifice and (0.39 ± 0.01) × 10−3 mm2/s after sacrifice. Multiple diffusion components were observed, consistent with flowing material, but the extra components did not increase with increased CO2. It is proposed that the additional components may be due to extracellular, extravascular water such as CSF. © 1991 Academic Press, Inc.
A dual‐frequency circularly polarizing whole‐body MR antenna for 69/170 MHz
Authors: Dürr W. , Rauch S. 
Published: March 2007

AbstractThe design concept of a dual‐frequency whole‐body MR antenna for circular polarization is presented. First, the principle of the capacitively shortened transmission line antenna, which is the basis of the design, is discussed. Emphasis is given to the antenna design at high frequencies. Two variants of possible antenna constructions are described and the RF efficiency is calculated for both frequencies. The antenna performance is discussed for the example of 69 and 170 MHz, the nuclear magnetic resonance frequencies of the nuclei 31P and 1H at 4 T. For 31P experiments, a whole‐body antenna is useful only for transmitting and, thus, the antenna performance can be optimized for 1H. The design principle is not limited to two frequencies; however, the RF efficiency decreases with an increasing number of resonance frequencies. Results of a laboratory version and 1H images at 4 T are presented. © 1991 Academic Press, Inc.
Multiecho, spin‐echo sequence to eliminate unwanted echoes
Authors: Zur Y. , Zou X. , Neuringerc L. J. 
Published: March 2007

AbstractTwo types of artifacts—a mirror‐reversed image about the phase‐encode direction and a wave‐like intensity variation across the image—may appear when using a conventional multiecho spin‐echo sequence. We describe and demonstrate a new method, which eliminates such artifacts, using only one excitation per phase‐encoding step and without the need for spoiler gradients. © 1991 Academic Press, Inc.
Longitudinal spin‐order‐based pulse sequence for lactate editing
Authors: Reddy Ravinder , Subramanian V. H. , Clark B. J. , Leigh John S. 
Published: March 2007

AbstractA new pulse sequence which edits proton spectra of lactate with full signal return and gives good suppression of water and fat signals is described. This sequence exploits longitudinal spin‐order from lactate to edit lactate from fat. Experimental results from phantoms and excised pig heart are presented. © 1991 Academic Press, Inc.
Rapid, fully automatic, arbitrary‐volume in vivo shimming
Authors: Webb Peter , Macovski Albert 
Published: March 2007

AbstractMR spectroscopy and many MR imaging methods benefit from a well‐shimmed magnet. We have developed a pulse sequence which enables fast and accurate measurement of three‐dimensional field maps in vivo, and a data analysis package that allows calculation of shim currents to optimally shim arbitrary selected volumes. A data link to the shim power supply allows automatic update of currents. No intervention by the operator is required. Typical in vivo shimming time is less than 5 min. Performance analysis, phantom, and in vivo results are presented. © 1991 Academic Press, Inc.
On the origin of paramagnetic inhomogeneity effects in whole blood
Authors: Matwiyoff N. A. , Gasparovic C. , Mazurchuk R. , Matwiyoff G. 
Published: March 2007

AbstractAsymmetric 7 T proton NMR signals of water in RBC suspensions containing intracellular deoxyhemoglobin are composites of chemically shifted extracellular and intracellular resonances broadened by gradient diffusion and modulated by transmembrane water exchange. This allows assessment of field dependences of acute hematoma intensities in proton MRIs at lower field strengths ( <1.5 T). © 1991 Academic Press, Inc.
31P MRS of myocardial inorganic phosphate using radiofrequency gradient echoes
Authors: Gober J. R. , Schwartz G. G. , Schaefer S. , Massie B. M. , Matson G. B. , Weiner M. W. , Karczmar G. S. 
Published: March 2007

AbstractDetermination of the chemical shift and integral of the myocardial intracellula inorganic phosphate (Pi) resonance by 31P magnetic resonance spectroscopy (MRS) is often precluded due to a large overlapping signal from 2,3‐diphosphoglycerate (2,3‐DPG) from chamber and myocardial blood. This report demonstrates the use of radiofrequency (RF) magnetic field gradient echoes (RFGE) to eliminate signals from 2,3‐DPG in flowing blood, while retaining signals from intracellular myocardial Pi, ATP, and phosphocreatine (PCr). The ECG‐triggered 31P spectra were acquired from the myocardium of open chest pigs using a Philips Gyroscan 2‐T magnetic resonance spectrometer. A 2.5‐cm‐diameter surface coil attached to the myocardium was used to provide the RF gradient as well as for excitation and detection of signals. Optimal performance of the RFGE pulse sequence was obtained when the RF gradient pulses were centered at peak diastole or peak systole. Under these conditions, 2, 3‐DPG signals were completely suppressed, and sensitivity was usually sufficient to allow detection of a well‐resolved Pi signal. Myocardial pH determined from RFGE experiments was 7.16 ± 0.10, and the ratio of the integrals of the Pi and ATP resonances (Pi/ATP) was 0.24. The mean signal‐to‐noise ratio (S/N) for PCr in control spectra acquired in 4 min was 19/1, while the mean S/N for PCr in RFGE‐edited spectra acquired in 15 min was 11/1, demonstrating that the present implementation of the RFGE method results in significant loss in sensitivity. These experiments demonstrate that RFGE‐editing allows accurate determination of the chemical shift and integral of the Pi resonance in blood‐perfused myocardium in situ. © 1991 Academic Press, Inc.
Localized in vivo proton spectroscopy of the human kidney
Authors: Shah N. J. , Carpenter T. A. , Wilkinson I. D. , Hall L. D. , Dixon A. K. , Freer C. E. L. , Prosser K. , Evans D. B. 
Published: March 2007

AbstractIn vivo 1H spectroscopy using the STEAM sequence for localization has been applied to the human kidney in normal volunteers and subjects with succesful renal transplants. We show that, within the resolution of our measurements, trimethylamines are present in the spectra from some of the subjects and absent from others, the prominent peak seen at 5.8 ppm in the spectrum is identified as that from urea and not lipid, as previously suggested. © 1991 Academic Press, Inc.
Measurements of pertinent concentrations of oxygen in vivo
Authors: Swartz H. M. , Boyer S. , Gast P. , Glockner J. F. , Hu H. , Liu K. J. , Moussavi M. , Norby S. W. , Vahidi N. , Walczak T. , Wu M. , Clarkson R. B. 
Published: March 2007

AbstractA new method able to measure the concentration of oxygen in complex biological systems, including in vivo, has been developed using low‐frequency EPR and newly characterized free radicals that are very sensitive to the concentration of oxygen. The free radicals (fusinite and lithium phthalocyanine) are very stable in tissues (for at least 150 days), apparently nontoxic, and can reflect oxygen concentrations that are less than the Km of cytochrome oxidase (0.1 μM or lower). Their biological stability is indicated by the fact that repeated measurements with fusinite of the concentration of oxygen in skeletal muscle have been made in the same animal for more than 150 days without any change in sensitivity or signs of toxicity. © 1991 Academic Press, Inc.
Correction for chemical‐shift artifacts in 19F imaging of PFOB: Simultaneous multislice imaging
Authors: Lee H. K. , Nalcioglu O. , Buxton R. B. 
Published: March 2007

AbstractOne of the difficulties encountered in 19F NMR imaging of fluorinated blood substitutes is that these compounds often exhibit complex multipeak spectra. These peaks result in chemical‐shift artifacts along the readout direction and blurred images. In addition, each peak excites a different slice (mis‐selection) when a slice selection gradient is applied during the selective rf pulse. A simultaneous multislice imaging method has been developed to solve the inherent problem of mis‐selection. The essence of this method is to use the two strongest peaks of the spectrum to excite controlled different multiple slices simultaneously, with or without a slice gap. The images corresponding to the two spectral lines are then separated from in‐and out‐of‐phase images (Dixon method). This method corrects the problem of mis‐selection and either improves the SNR or increases the number of slices over spectrally selective methods which image only one peak. © 1991 Academic Press, Inc.
Magnetic resonance imaging study of the rat cerebral ventricular system utilizing intracerebrally administered contrast agents
Authors: Wan Xiaoming , Fu Tsu‐Ching , Smith Paul H. , Brainard James R. , London Robert E. 
Published: March 2007

AbstractMagnetic resonance imaging (MRI) was employed to study the rat brain in conjunction with intracerebral (ic) injection of three contrast agents: GdHAM, GdDPTA, and MnCl2, The results demonstrate several advantages of ic administration of MRI contrast agents over the other routes of injection in examining CSF dynamics and brain ventricular structure. Apparent affinity of the luminal ventricular wall of the brain for positively charged GdHAM and Mn2+ ions is observed, presumably reflecting the presence of negatively charged wall components. Respiratory distress caused by (intravenous) injection of GdHAM was found to be minimized in the case of ic injections. Time‐dependent changes in observed contrast indicate that diffusive processes rather than flow of CSF play a dominant role in distributing the contrast agents. Possible applications of this approach in brain research are discussed. © 1991 Academic Press, Inc.
Quantitative determination of the partial oxygen pressure in the vitrectomized rabbit eye in Vivo using 19F NMR
Authors: Berkowitz Bruce A. , Wilson Charles A. , Hatchell Diane L. , London Robert E. 
Published: March 2007

AbstractWe have quantitatively determined the PO2 within the vitreous space of the vitrectomized rabbit eye in vivo using 19F NMR and perfluorotributylamine (FTBA). The results of the present work are in good agreement with previous measurements of PO2, within the nonvitrectimized rabbit eye obtained using oxygen microelectrodes. In this study, good precision and accuracy were achieved by: (1) having minimal flow effects present, (2) optimizing the signal‐to‐noise through the use of neat FTBA and surface coil transmission and detection, and (3) performing an inversion‐recovery pulse sequence, with adiabatic pulses, to optimize the dynamic range of the T1 experiment. Possible deleterious effects on the measured T1, due to the vitreal temperature gradient are discussed. To the best of our knowledge the results of this study demonstrate, for the first time, a quantitative determination of intraocular PO2 in vivo using 19F NMR and FTBA. © 1991 Academic Press, Inc.
Tumor bioenergetics and blood flow in RIF‐1 murine tumors treated with 5‐fluorouracil
Authors: Li Shi‐Jiang , Wehrle Janna P. , Glickson Jerry D. , Kumar Nirmal , Braunschweiger Paul G. 
Published: March 2007

AbstractTreatment of RIF‐1 solid tumors with 5‐fluorouracil (5‐FU, 100 or 200 mg/kg, ip) caused substantial regression of the tumors, with regrowth initiated on Day 6 (100 mg/kg) or Day 9 (200 mg/kg). Blood perfusion in the tumor, estimated by uptake of 86Rb+, was significantly increased after treatment with 5‐FU, while Rb+ uptake in normal tissues (skin, muscle) was unaffected. The increase in tumor perfusion during the first few days following treatment was significantly greater in animals treated with the higher dose of 5‐FU. Perfusion‐dependent 86Rb+ uptake returned to control levels by the 9th day after treatment with 100 mg/kg of 5‐FU, but remained elevated on Days 9–12 after the higher dose. By the lst day following treatment with 5‐FU, in vivo 31P NMR spectra of treated tumors indicated significantly higher ratios of phosphocreatine to Pi, higher pH, and lower ratios of Pi to nucleoside triphophates compared to untreated age‐matched controls. These changes persisted for 9 days following the lower 5‐FU dose and for at least 12 days following the higher dose. Treatment with 5‐FU induces profound, dose‐dependent changes in tumor bioenergetics, which may result, at least in part, from changes in tumor perfusion after cytoreduction. © 1991 Academic Press, Inc.
Quantitative study of the susceptibility difference between trabecular bone and bone marrow: Computer simulations
Authors: Majumdar S. 
Published: March 2007

AbstractInherent differences in tissue magnetic susceptibility produce inhomogeneities in the static magnetic field which give rise to an additional dephasing of the transverse magnetization in gradient‐echo images. The enhanced dephasing of the signal results in an increase of the apparent relaxation rate 1/T and a corresponding decrease in signal intensity. These effects have been used to explain the regional loss of marrow signal intensity in the appendicular skeleton, where in the presence of trabecular bone in the proximal tibia there is an enhanced loss of signal compared to the tibial shaft where there is no trabeculation. It has been postulated that differences in tissue magnetic susceptibility arising due to the marrow‐trabeculae interface give rise to magnetic field inhomogeneities and a reduced T. In this study computer simulations are used to determine whether susceptibility differences comparable to that between trabecular bone and tissue relate to the reduction of tissue T and whether the reduction in T is also related to the concentration and magnitude of susceptibility differences. In addition the effects of the spatial distribution of these particulate discontinuities in susceptibility on the measured relaxation time T are also estimated. This model demonstrates that 1/T increases as the number density and magnitude of such susceptibility differences increase. In a pixel of linear dimension L consisting of material simulating tissue water, the presence of circular point susceptibility differences of dimension 0.001 L with magnetic susceptibility equivalent to trabecular bone, 1/T, increases at a rate of 1.60 × 10−2 s−1 /N for N ranging from 25–2500. Differences in magnetic susceptibility that are less than that between soft tissue and trabecular bone are also modeled and the simulations demonstrate that differences in magnetic susceptibility, much lower than that between trabecular bone and tissue equivalent interfaces, also produce a relaxation rate enhancement in gradient‐echo images. © 1991 Academic Press, Inc.
Water–proton nuclear magnetic relaxation in heterogeneous systems: Hydrated lysozyme results
Authors: Lester Cathy Coolbaugh , Bryant Robert G. 
Published: March 2007

AbstractSpin‐lattice relaxation rates of water protons in hydrated immobilized lysozyme are measured as a function of magnetic field strength. The dependence of water relaxation versus hydration is presented from 35 to 55% by weight water content. The water‐proton relaxation is directly coupled to that of the protein and the coupling exists in the absence of chemical exchange. A model is applied where relaxation within the two proton phases is coupled through a dipolar cross‐relaxation mechanism as well as chemical exchange. The observed amplitudes of the water‐proton relaxation profiles scale with the ratio of protein to water protons as well as the protein‐proton relaxation rate. The field dependence of the protein‐proton spin‐lattice relaxation is presented in the presence of D2O where a cross‐relaxation coupling is absent. The coupled relaxation model accounts well for the NMR relaxation data as a function of magnetic field strength which is similar to measurements on other heterogeneous systems such as tissues. © 1991 Academic Press, Inc.