bluuebunny/crossref_metadata_2025_split huggingface dataset:
Targeted relaxation enhancement agents for MRI
Authors: Lauffer Randall B. 
Published: March 2007

AbstractThe design, relative merits, and initial applications of targeted relaxation enhancement agents, a new form of MRI contrast media, are briefly discussed. These agents are designed to bind reversibly to target macromolecules in a tissue of interest, thus enhancing water proton relaxation efficiency and MRI contrast. Initial applications for targeted agents include blood pool and hepatobiliary imaging. © 1991 Academic Press, Inc.
A new method for the evaluation of the liver injury by 19F MRS of 5‐fluorouracil
Authors: Harada Masafumi , Koga Keiko , Miura Iwao , Nishitani Hiromu 
Published: March 2007

AbstractAn investigation was made of 5‐fluorouracil metabolism in rat liver by 19F MRS. Fluoronucleotide synthesis increased markedly with liver injury and accelerated with uracil treatment, indicating that 19F MRS may serve as a new method for evaluating liver viability. © 1991 Academic Press, Inc.
“One‐shot” velocity microscopy: NMR imaging of motion using a single phase‐encoding step
Authors: Xia Yang , Callaghan Paul T. 
Published: March 2007

AbstractThe use of the pulsed gradient spin‐echo sequence in NMR microscopy enables the measurement of molecular translational motion and simultaneous construction of velocity and self‐diffusion images, a technique that has been termed dynamic NMR microscopy. In this method the PGSE contrast gradient is stepped in a fourth dimension (q space) and so is inherently inefficient. Provided that one is prepared to sacrifice some of the additional information provided by the multiple PGSE gradient approach, it is possible to construct a velocity image alone by means of a single PGSE phase‐encoding step. We illustrate applications of this method in which a signal from the stationary spins is nulled by the use of both gradient phase cycling and a final “z‐storage” rf pulse. The limits to velocity resolution are around 10μm s−1 in free water but can be considerably smaller for molecules with a low self‐diffusion coefficient. We demonstrate this method in a study of water capillary flow at 12 μm transverse pixel resolution, extending the velocity range by employing a four‐quadrant analysis method. This method is also used to measure vascular transport in a living plant and find a flow rate of around 45μm s−1. © 1992 Academic Press, Inc.
Formulation of radiographically detectable gastrointestinal contrast agents for magnetic resonance imaging: Effects of a barium sulfate additive on MR contrast agent effectiveness
Authors: Rubin Daniel L. , Muller Holde H. , Young Stuart W. 
Published: March 2007

AbstractComplete and homogeneous distribution of gastrointestinal (GI) contrast media are important factors for their effective use in computed tomography as well as in magnetic resonance (MR) imaging. A radiographic method (using fluoroscopy or spot films) could be effective for monitoring intestinal filling with GI contrast agents for MR imaging (GICMR), but it would require the addition of a radiopaque agent to most GICMR. This study was conducted to determine the minimum amount of barium additive necessary to be radiographically visible and to evaluate whether this additive influences the signal characteristics of the GICMR. A variety of barium sulfate preparations (3‐12% wt/vol) were tested in dogs to determine the minimum quantity needed to make the administered agent visible during fluoroscopy and on abdominal radiographs. Solutions of 10 different potential GI contrast agents (Gd‐DTPA, ferric ammonium citrate, Mn‐DPDP, chromium‐EDTA, gadolinium‐oxalate, ferrite particles, water, mineral oil, lipid emulsion, and methylcellulose) were prepared without (“nondoped”) and with (“doped”) the barium sulfate additive. MR images of the solutions in tubes were obtained at 0.38 T using 10 different spin‐echo pulse sequences. Region of interest (ROI) measurements of contrast agent signal intensity (SI) were made. In addition, for the paramagnetic contrast media, the longitudinal and transverse relaxivity (R1 and R2) were measured. A 6% wt/vol suspension of barium was the smallest concentration yielding adequate radiopacity in the GI tract. Except for gadolinium‐oxalate, there was no statistically significant difference in SI for doped and nondoped solutions with most pulse sequences used. In addition, the doped and nondoped solutions yielded R1 and R2 values which were comparable. We conclude that barium sulfate 6% wt/vol added to MR contrast agents produces a suspension with sufficient radiodensity to be viewed radiographically, and it does not cause significant alteration in the MR signal appearance of most GICMR. These formulations can be useful for achieving optimal filling of the gastrointestinal tract prior to MRI. © 1992 Academic Press, Inc.
Reduction of RF penetration effects in high field imaging
Authors: Foo Thomas K. F. , Hayes Cecil E. , Kang Yoon‐Won 
Published: March 2007

AbstractA method of correcting for the RF inhomogeneity in the body by dielectric loading of the coil‐to‐shield space in an RF resonator (coil and shield assembly) is described. The presence of the RF coil and RF shield have significant effects on RF homogeneity. Based on theoretical calculations, a method for adjusting the RF homogeneity by manipulating the axial propagation constant, kz, is proposed. This is accomplished by loading the coil‐to‐shield space with dielectric material of suitable relative permittivity so as to increase kz and decrease the radial propagation constant, kp. In this manner, the radial wavelength (λp, = 2π/kp) can be increased relative to the body dimensions, and the field amplitude variations in the axial plane minimized. Theoretical calculations indicate that a value of between 30 and 40 for the relative permittivity of the dielectric material in the coil‐to‐shield space would reduce the RF field inhomogeneity from ±15% to about ±3% over a central 30‐cm‐diameter region of a homogeneous 40‐cm‐diameter body at both 64 and 170 MHz. The theoretical model was verified in laboratory measurements of the |B1|, field generated in a test coil at 170 MHz which was scaled to correspond to a body at 64 MHz. However, the improved RF field homogeneity would be accompanied by increased RF power requirements and reduced coil sensitivity. © 1992 Academic Press, Inc.
Image reconstruction for echo planar imaging with nonequidistant k‐space sampling
Authors: Bruder H. , Fischer H. , Reinfelder H.‐E. , Schmitt F. 
Published: March 2007

AbstractEcho planar imaging is characterized by scanning the 2D k‐space after a single excitation. Different sampling patterns have been proposed. A technically feasible method uses a sinusoidal readout gradient resulting in measured data that does not sample k‐space in an equidistant manner. In order to employ a conventional 2D‐FFT image reconstruction, the data have to be converted to a Cartesian grid. This can be done either by interpolation or alternatively by a generalized transformation. Filtering methods are described to minimize ghosting artifact that is typical in echo planar imaging. Results both from computer simulation and from experiments will be presented. Experimental images were obtained using a 2‐T whole‐body research system. © 1992 Academic Press, Inc.
The longitudinal relaxation time (T1) of the intracellular 23Na NMR signal in the isolated perfused rat heart during hypoxia and reoxygenation
Authors: Prince Lawrence S. , Miller Sandra K. , Pohost Gerald M. , Elgavish Gabriel A. 
Published: March 2007

AbstractEach of six perfused rat hearts was subjected to 30 min of hypoxia followed by 60 min of reoxygenation. Inversion‐recovery data on the intracellular Na NMR signal, differentiated by a shift reagent, 6 mM Dy(PPP)2, were obtained every 5 min, and T1 values were calculated. The T1 of the intracellular Na signal did not show any significant change either during hypoxia or upon reoxygenation, although the level of Nai increased about 50%. Such an increase of total Nai, is expected to reduce the observed relaxation rate by diluting the fraction of Nai, ions that interact with intracellular polyelectrolytes. The observed constancy of T1 in our study is explained on the basis of the typical values of the dissociation constants of sodium ions, in aqueous solutions, in interaction with polyelectrolytes. Although the constancy of intracellular sodium T1 during hypoxia may preclude the utilization of T1, weighting for the monitoring of pathology, its determination could be important for setting optimal acquisition times in high time‐resolution experiments. © 1992 Academic Press, Inc.
Shielded gradient coils and radio frequency probes for high‐resolution imaging of rat brains
Authors: Jasinski Andrzej , Jakubowski Tomasz , Rydzy Marek , Morris Paul , Smith Ian C. P. , Kozlowski Piotr , Saunders John K. 
Published: March 2007

AbstractA shielded gradient system and radio frequency probes for a 4.7‐T/30‐cm horizontal bore magnet are described. The systems were designed principally to obtain images and localized spectra from rat brains. The gradients can operate in either a shielded or non shielded mode. The rf probe, which combines both highest sensitivity and highest resolution, consists of a large modified saddle type transmitter and a small surface reception coil, actively decoupled using diodes. The system performance is demonstrated on phantoms and on a rat brain, where an image with in plane resolution of 80μ m and a slice thickness of 150 μm is obtained. © 1992 Academic Press, Inc.
Magnetic resonance imaging of the uterine cervix using an intravaginal coil
Authors: Baudouin C. J. , Soutter W. P. , Gilderdale D. J. , Coutts G. A. 
Published: March 2007

AbstractCylindrical receiver coils designed for intravaginal use were utilized to image the uterine cervix. Good quality images of the cervix, vaginal wall, and parametrium were obtained and patient tolerance of the procedure was good. © 1992 Academic Press, Inc.
In vivo dynamic MR imaging of MBP‐induced acute experimental allergic encephalomyelitis in Lewis rat
Authors: Namaer I. J. , Steibel J. , Poulet P. , Armspach J. P. , Mauss Y. , Chambron J. 
Published: March 2007

AbstractA dynamic in vivo study by MRI consisting of the measurement of relaxation times and in the visualization of the BBB permeability by Gd—DOTA was performed in an MBP‐induced acute EAE model of Lewis rat. Fourteen rats were immunized with an MBP/CFA mixture, eight by CFA alone, and three control rats were used to test the harmless effect of repeatedly performed MRI examinations. Beginning on the 8th or 9th days and in parallel with the emergence of clinical signs, rats immunized by the MBP/CFA mixture showed slight increases of relaxation times and of the BBB permeability. These abnormalities which always remain localized in the periventricular regions, become more pronounced toward the 10th and 11th days, just before (or at the same time) as paraplegia manifestations. After a plateau of a few days, they diminish with the clinical signs. This close correlation found in vivo establishes the essential role of BBB in the pathogenesis of clinical signs of this EAE model. © 1992 Academic Press, Inc.
31P MRS as an early prognostic indicator of patient response to chemotherapy
Authors: Redmond O. M. , Stack J. P. , O'Connor N. G. , Carney D. N. , Dervan P. A. , Hurson B. J. , Ennis J. T. 
Published: March 2007

AbstractIn this study 31P spectral changes were closely monitored following the initial administration of cytotoxic drugs and related to five parameters of patient response. Pre‐ and postchemotherapy 31P MRS examinations were performed on 16 patients with large, malignant tumors. These included four tumor types: (i) lymphoma (n = 7),(ii) breast carcinoma (n = 4), (iii) musculoskeletal tumors (n = 4), and (iv) adenocarcinoma (n = 1). A mean of 5 spectra/patient (range 2–10) was performed following the initial chemotherapy. The spectral trends exhibited by 14 of 16 patients reached “points of maximum change,” after which they began to revert toward prechemotherapy values. In 2 of 16 patients that did not respond to the initial chemotherapy regimen, no spectral trends were observed. The degree of change of certain spectral parameters, namely, decreases in PME, PME/ PDE, PME/PCr, PME/NTP, PDE/PCr, and tumor pH, as well as increases in the ratios Pi/PME and Pi/PDE, were associated with good patient response and separated responders from nonresponders. Pi/PME appears the most promising for discriminating partial from Complete responders.
Detection of significant features and statistical analysis of 2D and 3D images of 31p metabolites
Authors: Nelson Sarah J. , Vigneron Daniel B. , Brown Truman R. 
Published: March 2007

AbstractThe application of spectroscopy techniques to the study of normal and pathological tissue is currently limited by the difficulties of acquiring precisely localized spectraand analyzing the resulting, relatively low signal‐to‐noise data. Interpretation of multivoxel spectroscopy data is greatly facilitated by estimating peak parameters and representing their spatial distribution as metabolite images. We present herethe new algorithm MIM‐STATS, which performs an analysisof these images and determines whether the variations in the images are statistically significant. The algorithmhas been developed and tested by application to 31P CSI data from the human forearm and brain. Our results demonstrate that MIMSTATS can detect signal at a very low signal‐to‐noise ratio in a reliable and reproducible fashion and provides a sound basis for testinghypotheses concerning differences in distribution of metabolites.
Analysis of the temporal and spatial dependence of the Eddy current fields in a 40‐cm bore magnet
Authors: Robertson S. , Hughes D. G. , Liu Q. , Allen P. S. 
Published: March 2007

AbstractEddy current fields, generated in an animal‐size superconducting NMR magnet by a nominally rectangular pulsed transverse gradient applied in the vertical direction, have been studied by measuring the offset frequency of the proton NMR signal obtained from a small spherical sample. Measurements were made, after various time delays, at nine different locations in the sample space. Analysis of the data shows that the time‐dependent fields at all nine locations are quite well accounted for by the superposition of only four independent exponentially decaying components that have time constants in the range from 9 to 400 ms. Two of these were found to be caused by eddy currents generated in the magnet structure. They generate primarily linear gradients, though one of them also produces a B0 shift, indicating a significant asymmetry about the isocenter of the conducting structure in which the eddy current flows. The other two exponentially decaying components, which had very different time constants from the eddy currents and also initial amplitudes of the opposite sign, were generated by the preemphasis unit. This calls into question the procedure used to adjust the preemphasis unit and an alternative method is proposed.
Analysis of encoding efficiency in MR imaging of velocity magnitude and direction
Authors: Contur Thomas E. , Robinson Bruce H. 
Published: March 2007

AbstractThe efficiency of balanced versus unbalanced techniques for phase‐angle‐based velocity magnitude and direction imaging is investigated. Methods having balanced flow‐encoding gradients (gradients in positive and negative directions with a zero center of gravity) are compared with unbalanced methods. For three‐dimensional imaging, a currently used balanced method is the six‐point technique having opposed gradients pairs for each orthogonal direction. A currently used unbalanced method is a four‐point null technique which has three orthogonal gradients and an additional acquisition having no specific flow encoding to correct the baseline (null) phase. In the gradient‐limited case of slow flow and perfusion. the balanced method is predicted to have higher velocity magnitude‐to‐noise ratio per time (SNRv) by a factor of 1.63, with similar results for velocity direction. In the wraparound‐limited case of faster flows and motions, similar results are found when a null acquisition is added to the balanced method. This results in a seven‐point balanced method having an SNRv, 1.51 times that of the four‐point unbalanced method. If null phases are within the [–π/2, π/2] interval, this additional null acquisition is unnecessary. Other four‐point methods are also considered. These results indicate that, in general, balanced methods have advantages over unbalanced methods for velocity imaging. © 1992 Academic Press, Inc.
The application of 13C NMR to the characterization of phospholipid metabolism in cells
Authors: Ronen Sabrina M. , Degani Hadassa 
Published: March 2007

Abstract31P and 31C NMR spectroscopy of lipid extracts of T47D human breast cancer spheroids and the use of 13C‐labeled lipid precursors [3‐13C ] serine, [1,2‐13C] ethanolamine, and [1,2‐13C]choline enabled us to determine the rate of 13C incorporation into the major phos‐pholipids and to show that the synthesis of phosphatidylethanolarnine in T47D cells is via both the CDP‐ethanolamine pathway and serine decarboxylation, with the extent of each depending on the concentration of ethanolamine in the medium. In the presence of low ethanolamine (3.4 μ M), both pathways contribute in equal proportions, while in the presence of high ethanolamine, the CDP‐ethanolamine pathway predominates. © 1992 Academic Press, Inc.
Theory of contrast agents in magnetic resonance imaging: Coupling of spin relaxation and transport
Authors: Bauer W. R. , Schculten K. 
Published: March 2007

AbstractThe role of diffusive transport on the enhancement of nuclear spin relaxation through NMR contrast agents is described by means of diffusion‐Bloch equations. These equations are solved in the mean relaxation time approximation [W. Nadler and K. Schulten, J. Chem. Phys. 82, 151‐160 (1985)]. A model presented considers relaxation enhancement in tissue in which contrast agents confined to intravascular spaces affect nuclear spin in the extravascular volume. We show how the mean relaxation time depends on capillary density, on permeability, and on diffusion. A second model describes enhanced phase relaxation of liver tissue in the presence of magnetic particles in Kupffer cells. The relationship between relaxation rate and density of Kupffer cells is investigated. The diagnostic value of enhanced nuclear relaxation in the presence of contrast agents is discussed on the basis of the systematic mathematical results obtained.
31P NMR of electrically stimulated rectus femoris muscle: An in vivo graded exercise model
Authors: Matheson Gordon O. , Mckenzie Donald C. , Gheorghiu Daniel , Ellinger David C. , Quinney H. Arthur , Allen Peter S. 
Published: March 2007

AbstractThis study reports on the development of a model for studying skeletal muscle metabolism in humans using NMR spectroscopy. Graded exercise was simulated using electrical stimulation in 10 healthy, fit subjects (mean VO2max = 53 ± 4 ml. kg‐1 min‐1). The effects of varying the stimulation parameters, namely, the stimulation frequency, the stimulation intensity, and the duty cycle, as well as the spectral interrogation volume, were compared using data acquired from the rectus femoris muscle. With stimulation, the inorganic phosphate to phosphocreatine concentration ratio ([P1]/ [PCr]) and the intracellular pH both follow curvilinear relationships over the stimulation frequencies from 3 to 30 Hz, with the magnitude of the observed change related closely to stimulation intensity and duty cycle. Oxidative phosphorylation predominates at stimulation frequencies below 12 Hz, while anaerobic metabolism increases sharply above 12 Hz. Our findings show clearly the interdependence of the effects of the various stimulation parameters and emphasize the care that must be exercised in interpreting the physiological significance of the biochemical data obtained from electrical stimulation models used to study skeletal muscle metabolism.
Proton nuclear magnetic resonance lineshape studies on human blood plasma lipids from newborn infants, healthy adults, and adults with tumors
Authors: Hiltunen Y. , Ala‐Korpela M. , Jokisaari J. , Eskelinen S. , Kiviniitty K. 
Published: March 2007

AbstractThe usefulness of proton NMR spectroscopy of human blood plasma for cancer research has been extensively studied in recent years. Two main starting points have been offered by Fossel et al. (N. Engl. J. Med. 315, 1369 (1986)) and Mountford et al. (FEBS Lett. 203, 164 (1986)). In this work the experimental proton NMR spectra of blood plasma were analyzed with the aid of the multivariate lineshape fitting method. An appropriate model structure, in terms of the various lipoprotein (VLDL, LDL. and HDL) signals, for the methylene region was used. Neonates, healthy adults, and adults with nonmalignant and malignant tumors were studied. The linewidth of the methylene region was found to be linearly dependent on the relative concentrations of the lipoproteins. The correlation coefficient was ‐0.89 (P < 0.001) for VLDL and 0.88 (P < 0.00 1) for HDL. A correlation between VLDL concentration and age, 0.76 (P < 0.001), was also established. VLDL was modeled using two components. The half‐linewidth of the lower field component was slightly elevated for the adults with large metastases. This might be in association with the fucose‐containing proteolipid complex detected earlier in cancer cells or in sera of cancer patients. Some signals of this complex may fall in the same region of the spectra. The spectra for the neonates were indicated to be totally different from the adults. This and other related questions were explained by means of the model parameters and the relative concentrations of the lipoproteins VLDL, LDL, and HDL. The presented technique can be used as a rapid research tool for figuring out the relative concentrations of the lipoproteins in blood plasma and explaining the reasons behind the changes in the spectra.
Rapid T1 estimation using tagged magnetization‐prepared gradient‐echo MR imaging
Authors: Niitsu Mamoru , Campeau Norbert G. , Riederer Stephen J. , Anno Izumi , Itai Yuji 
Published: March 2007

AbstractA technique for estimation of the longitudinal relaxation time of a large homogeneous object with an acquisition time of 4s or less was developed by combining spatially selective rf tagging pulses with a T1‐weighted magnetization‐prepared gradient‐echo sequence. Multiple 5‐mm‐wide tagged areas are laid orthogonal to the imaging section of interest. The contrast between each tag and the untagged regions differs because each tag is produced at a different time. The T1 value is determined from the nulling time at which tagged and untagged areas have no contrast.
Effect of lithium on the double‐quantum behavior of 23na in normal human erythrocytes
Authors: Gullapalli Rao P. , Hawk Roger M. , Komorosk Richard A. 
Published: March 2007

AbstractThe doublé‐quantum behavior of 23Na in the presence of different concentrations of Li in human erythrocytes was investigated. The 23Na double‐quantum signal was quenched in both the extracellular and the intracellular compartments with increasing concentration of Li in each compartment, along with an increase in the 23Na T1 both intra‐ and extracellularly. Some extracellular quenching could be observed at the near therapeutic concentration of 2 mM Li. The ratio of slow to fast spin‐spin (T2) relaxation times, obtained from the dependence of the double‐quantum signal on creation time, approached unity at an overall Li concentration of 40 mM. These results provide evidence that Li and Na compete for both intra‐ and extracellular binding sites in erythrocytes.