bluuebunny/crossref_metadata_2025_split huggingface dataset:
Determination of extracellular/intracellular fluid ratios from magnetic resonance images: Accuracy, feasibility, and implementation
Authors: Martin M. A. , Tatton W. G. , Lemaire C. , Armstrong R. L. 
Published: March 2007

AbstractThis study determines the accuracy and feasibility of using localized spin‐lattice (T1) relaxation time measurements from magnetic resonance (MR) images to follow changes in extracellular/intracellular fluid ratios in defined subvolumes of living tissue. A red blood cell suspension was used as a test system and a simple two‐compartment model incorporating fast exchange was found to suffice for the conversion of T1 values to volume ratios. The technique requires the addition of gadolinium‐DTPA to the model system to selectively enhance relaxation in the extracellular fluid space. No detectable amount of gadolinium‐DTPA was found to enter the intracellular fluid space, and all magnetization decay plots obtained from both intracellular constituents and complete RBC suspensions consisted of a single exponential. Both of these results are compatible with assumptions underlying our physical model. The NMR‐determined fluid ratio values were compared to those measured via the microhematocrit technique. Partial saturation image‐mode determinations are strongly correlated to microhematocrit data (R2 = 0.945) and indicate that localized cell volume changes may be followed with a sensitivity of ±2.2%. These values compare favorably with those produced when nonimaging inversion‐recovery techniques are used to determine the MR hematocrit (R2 = 0.962, sensitivity = ±1.1%). This technique, with modification, should be applicable to the comparison of ratios of extracellular/intracellular fluid volumes in structurally complex tissues where small subvolumes of homogeneous cell structure could be examined. © 1990 Academic Press, Inc.
In vitro31P NMR spectroscopy of the reproductive organs of the male rat: An improved preparation method
Authors: Van Grond J. Der , Seijkens D. , Mali W. P. Th. M. 
Published: March 2007

AbstractIn vitro 31P spectroscopy can be applied to disentangle the broad resonances in in vivo 31P NMR spectra of the reproductive organs of the male rat. However, adenosinetriphosphate (ATP) and glycerophosphocholine (GPC), present in large amounts in vivo, are nearly completely absent in vitro. With a modified PCA extraction method, in which the organs were lyophilized before extraction, a large amount of ATP and GPC could be found in vitro. This new extraction method is probably not only restricted to in vitro analysis of the testis but is likely to be useful for analysis of other organs such as kidney and liver. © 1990 Academic Press, Inc.
CPMG imaging sequences for high field in vivo transverse relaxation studies
Authors: Mulkern R. V. , Wong S. T. S. , Jakab P. , Bleier A. R. , Sandor T. , Jolesz F. A. 
Published: March 2007

AbstractTwo‐dimensional Fourier transform Cam‐Purcell‐Meiboom‐Gill (CPMG) imaging sequences were implemented on 1.9‐T and 1.5‐T imaging systems in order to test their ability to characterize in vivo transverse decay curves (TDCs). Both hard‐ and soft‐pulse CPMG imaging sequences, consisting of up to 128 echoes with echo spacings of approximately 10 ms were developed, implemented, and tested. These sequences provide one of the most detailed samplings of TDCs from image data sets reported to date. Good agreement between image‐extracted T2 values and spectroscopically obtained T2 values of NiCl2‐doped saline solutions was found with both hard‐ and soft‐pulse sequences. In vivo TDCs were extracted from rabbit and human image data sets. For several tissues, biexponential TDC fits provided considerable improvement over monoexponential fits and the sensitivity of the fitting parameters to positive baseline offsets was examined. With the time coverage of the relaxation decay curves available from these sequences, the TDCs from white matter in humans appear largely monoexponential while those from cortical grey matter demonstrate biexponential behavior. © 1990 Academic Press, Inc.
Magnetic susceptibility shift selected imaging: MESSI
Authors: Xu Yan , Balschi James A. , Springer Charles S. 
Published: March 2007

AbstractParamagnetic compounds are often used to enhance contrast in MRI by virtue of their increase in the kinetics of the relaxation of water 1H magnetization. Here, we demonstrate a method for contrast enhancement which is based on the resonance frequency shifts caused by the bulk magnetic susceptibility (BMS) effects of such compounds. This involves the frequency selective excitation in the absence of field gradients, during the imaging sequence, of a portion of the water 1H resonance which is rendered inhomogeneous by BMS shifts only. The image which results is of that portion of the sample which gives rise to the portion of the spectrum excited. A phantom sample which simulates some aspects of tissue, particularly blood vessels with different orientations in the magnetic field, was prepared. The contrast enhancement exhibited here avoids some of the distortions attendant to the use of paramagnetic reagents. This new approach can, in principle, utilize the natural BMS differences found in all tissue. © 1990 Academic Press, Inc.
Tissue perfusion in humans studied by fourier velocity distribution, line scan, and echo‐planar imaging
Authors: Feinberg David A. , Jakab Peter D. 
Published: March 2007

AbstractIn tissue perfusion studies, FT velocity distribution imaging (VDI) intrinsically distinguishes signals from moving blood and volume‐averaged tissue. Results in human thyroid gland, in vivo, using VDI line scan technique demonstrated separation of moving blood signal from glandular tissue. while VDI inner‐volume echo‐planar imaging of brain showed only CSF velocity above the image noise level. New alternating polarity gradient sequences which permit separation of diffusion and slow velocity are discussed. A novel method of 3D FT imaging (two spatial and one velocity dimension) combining inner‐volume imaging and echo‐planar imaging with velocity resolution of 0.15 mm / s per pixel is demonstrated. A novel graphical method of calculation and display of diffusion dependence in pulsed gradient sequences is presented. © 1990 Academic Press, Inc.
Sodium‐23 MR imaging of the kidney in guinea pig at 2.1 T, following arterial, venous, and ureteral ligation
Authors: Maeda Munehiro , Seo Yoshiteru , Murakami Masataka , Kuki Satoru , Watari Hiroshi , Iwasaki Satoru , Uchida Hideo 
Published: March 2007

AbstractIn vivo 23Na magnetic resonance images of guinea pig kidney were obtained at 2.1 T using a spin‐echo sequence with an echo time of 19 ms. The intact kidney showed a very strong signal intensity in the sodium image. The signal intensity of the kidney decreased to 55% after ligation of the renal artery together with the vein and the ureter. The total sodium content in the excised kidney after arterial occlusion, measured by flame photometry, was 24% higher than that in the intact kidney. The transverse relaxation time (T2) of the extracellular sodium in the isolated kidney decreased to one‐third of that in the intact kidney. This shortening of T2 may be partly responsible for the decrease in the 23Na signal intensity from the kidney after arterial occlusion. © 1990 Academic Press, Inc.
Variable NMR visibility of intracellular sodium induced by Na+‐substrate cotransport in dog cortical tubules
Authors: Ammann H. , Boulanger Y. , Vinay P. 
Published: March 2007

AbstractThe intracellular sodium concentration ([Na +]i) of dog kidney cortical tubules was monitored by flame photometry and 23Na NMR using dysprosium tripolyphosphate as shift reagent. Upon addition of substrates cotransported with sodium, flame photometry showed an increase in [Na+]i while no change (glutamine, glucose) or even a decrease (lactate) in the Na NMR signal was observed. This discrepancy could not be explained by a lack of ATP prior to the addition of substrates or by a decrease of NMR visibility of Na induced by binding of substrate to membrane transporters (and pump). We propose that a variation of the “apparent visibility” of Na may occur, arising from either a compartmentation of Na in dog cortical tubules or an inhomogeneous extracellular distribution of the shift reagent. © 1990 Academic Press, Inc.
Elimination of signal strength dependency upon coil loading–an aid to metabolite quantitation when the sample volume changes
Authors: Hoult David I. , Deslauriers Roxanne 
Published: March 2007

AbstractThe phase, height, and width of NMR spectral lines from a constant number of nuclei are frequently dependent upon changes in probe Q factor and tuning, caused by motion of the sample and/or changes in its electrical conductivity and size. Thus quantitation of metabolites in biological samples can be difficult. When probe tuning and matching are rendered independent by the use of a tuned coupling coil for matching, use of a very low input impedance preamplifier can virtually eliminate such dependencies in the received signal. Likewise, by reciprocity, the use of a low output impedance transmitter greatly reduces the dependence of pulse flip angle upon sample characteristics. Experimental results verifying these statements are presented, and the time course of signals from a swelling, perfused pig heart and an external reference are plotted. © 1990 Academic Press, Inc.
Direct carbon versus proton heteronuclear editing of 2‐13C ethanol in rabbit brain in vivo: A sensitivity comparison
Authors: Novotny Edward J. , Ogino Takashi , Rothman Douglas L. , Petroff Ognen A. C. , Prichard James W. , Shulman Robert G. 
Published: March 2007

AbstractProton NMR editing techniques were utilized to study the pharmacology of 13C‐labeled ethanol in the cerebrum of the living rabbit at 4.7 T. The sensitivity of these proton spectroscopic methods was compared to direct carbon spectroscopy and a 14‐fold improvement in sensitivity of 1H over 13C NMR spectroscopy was observed in vivo. This increase in sensitivity permitted the observation of the time course of the influx and afflux of this 13C‐labeled compound with a time resolution of approximately 2 min per spectrum. © 1990 Academic Press, Inc.
In vivo volume‐selective metabolite editing via correlated z‐order
Authors: Brereton Ian M. , Rose Stephen E. , Galloway Graham J. , Moxon Leith N. , Doddrell David M. 
Published: March 2007

AbstractVolume‐selected 1H NMR spectroscopy was combined with spectral editing to selectively detect brain metabolites. The SPACE localization sequence was used to create a voxel of z‐magnetization which could then be edited for any scalar coupled metabolite by the use of selective excitation in the ECZOTIC sequence to generate longitudinal spin order. The sequence returns an edited signal with no intrinsic loss of magnetization. The method was applied to observe approximately 10 m M ethanol and 17 mM lactate in the brain of a dog. © 1990 Academic Press, Inc.
Human brainstem auditory evoked potentials (BAEP) before and after MR examinations
Authors: Müller S. , Hotz M. 
Published: March 2007

AbstractRecently significant changes of human brainstem auditory evoked potentials (BAEP) after exposure to static magnetic fields were reported (L. von Klitzing, Clin. Physiol. Meas. 7(2), 157 (1986); L. Stojan, D. Sperber, and K. Dransfeld, Naturwissenschaften 75, 622 (1988)). We recorded BAEPs of 11 subjects before and after a routine MRI examination at 1.5 T. In addition the BAEP of a healthy volunteer was measured in five different static magnetic fields (0‐2.0 T). Our results indicate that routine MRI investigations do not significantly alter the interpeak latencies of the BAEPs. © 1990 Academic Press, Inc.
Application of volume‐selected, two‐dimensional multiple‐quantum editing in vivo to observe cerebral metabolites
Authors: Crozier Stuart , Brereton Ian M. , Rose Stephen E. , Field James , Shannon Gerald F. , Doddrell David M. 
Published: March 2007

AbstractThe volume selection technique SPACE has been combined with a two‐dimensional multiple‐quantum editing sequence to uniquely detect certain J‐coupled cerebral metabolites. In vivo results demonstrating edited glutamate/glutamine and lactate from 0.4 ml of a rat's brain at 4.7 T are presented. The sequence was optimized to balance multiple‐quantum generation and signal loss due to T2 relaxation. Without due regard to T2 relaxation little signal is observed. © 1990 Academic Press, Inc.
Factors affecting 39K NMR detectability in rat tissue
Authors: Rashid S. Abdul , Adam W. R. , Craik D. J. , Shehan B. P. , Wellard R. M. 
Published: March 2007

AbstractIn this study we have found that NMR detectability of 39K in rat thigh muscle may be substantially higher (up to 100% of total tissue potassium) than values previously reported of around 40%. The signal was found to consist of two superimposed components, one broad and one narrow, of approximately equal area. Investigations involving improvements in spectral parameters such as signal‐to‐noise ratio and baseline roll, together with computer simulations of spectra, show that the quality of the spectra has a major effect on the amount of signal detected, which is largely due to the loss of detectability of the broad signal component. In particular, lower‐field spectrometers using conventional probes and detection methods generally have poorer signal‐to‐noise and worse baseline roll artifacts, which make detection of a broad component of the muscle signal difficult. © 1991 Academic Press, Inc.
MR Contrast Due to Microscopically Heterogeneous Magnetic Susceptibility: Numerical Simulations and Applications to Cerebral Physiology
Authors: Fisel C. Richard , Ackerman Jerome L. , Buxton Richard B. , Garrido Leoncio , Belliveau John W. , Rosen Bruce R. , Brady Thomas J. 
Published: March 2007

AbstractWe calculate the effects of subvoxel variations in magnetic susceptibility on MR image intensity for spin‐echo (SE) and gradient‐echo (GE) experiments for a range of microscopic physical parameters. The model used neglects the overlap of gradients from one magnetic inclusion to the next, and so is valid for low volume fractions and weak perturbations of the magnetic field. Transverse relaxation is predicted to deviate significantly from linear exponential decay in both SE and GE at a particle radius of 2.5 μm. Calculated changes in transverse relaxation rates for SE and GE increase linearly with volume fraction of high‐susceptibility regions of 5 μm diameter, but increase with about the 3/2 power of volume fraction of regions with 15 μm spacing between centers. This sensitivity to the actual size and spacing of magnetized regions may allow them to be measured on the basis of contrast, without being resolved in images. GE and SE decay rates are approximately twice as sensitive to long cylinders of 5 μm diameter than to spheres of the same size, for diffusion constants of 2.5 μm2/ms. Calculated changes in transverse decay rates increase with approximately the square of field and susceptibility variation for 5‐μm spheres and a diffusion constant of 2.5 μm2/ms. This exponent is smaller for cylindrical magnetized regions of the same size, and also depends on the diffusion constant. We discuss possible applications of our theoretical results to the analysis of the effects of high‐susceptibility contrast agents in brain. Experimental data from the literature are compared with calculated signal changes according to the model. The monotonic dependence of decay rates on the volume of distribution of the contrast agent suggests that cerebral blood volume and flow could be measured using MR contrast. © 1991 Academic Press, Inc.
MR angiography by multiple thin slab 3D acquisition
Authors: Parker Dennis L. , Yuan Chun , Blatter Duane D. 
Published: March 2007

AbstractMultiple overlapping thin 3D slab acquisition is presented as a magnitude contrast (time
of flight) technique which combines advantages from multiple thin slice 2D and direct
3D volume acquisitions to obtain high‐resolution cross‐sectional images of vessel detail.
Details of implementation and example images are presented. ©1991 Academic Press, Inc.
Peak assignment in automatic data analysis
Authors: Haselgrove John , Elliott Mark 
Published: March 2007

AbstractLinear prediction algorithms are able to identify peaks in an NMR spectrum, but are not able to assign these peaks to components anticipated in the spectrum. We have developed an artificial‐intelligence protocol which uses the output parameter list from an LPSVD algorithm, and automatically assigns the peaks on the basis of an anticipated list of components. To overcome the influence of experimental conditions on the absolute values of frequency, integrated area, and linewidth, the assignment routine performs an internal scaling of the data by comparing all possible pairs of peaks in the spectrum. Completely automated analysis of large numbers ofin vivoFIDs is now possible. © 1991 Academic Press, Inc.
Comparison of diffusion‐ and T2‐weighted MRI for the early detection of cerebral ischemia and reperfusion in rats
Authors: Mintorovitch J. , Moseley M. E. , Chileuitt L. , Shimizu H. , Cohen Y. , Weinstein P. R. 
Published: March 2007

AbstractThe sensitivity of diffusion‐weighted MRI was compared to that of T2‐weighted MRI following temporary middle cerebral artery occlusion (MCA‐0) for 33 min followed by 4 h of reperfusion in rats. Diffusion‐weighted spin‐echo images using strong gradients (b value of 1413 s/mm2) demonstrated a significant increase in signal intensity in ischemic regions as early as 14 min after onset of ischemia in comparison to the normal, contralateral hemisphere (p < 0.05). This hyperintensity returned to baseline levels during reperfusion. T2‐weighted images showed no evidence of brain injury during the temporary occlusion. In three rats subjected to permanent MCA‐0, diffusion‐weighted MRI demonstrated an increased signal intensity on the first image following occlusion and continued to increase during the 4‐h observation period. T2‐weighted images failed to demonstrate significant injury until approximately 2 h after MCA‐O. Signal intensity ratios of ischemic to normal tissues were greater in the diffusion‐weighted images than in the T2‐weighted MR images at all time points (p < 0.05). Close anatomical correlation was found between the early and sustained increase in diffusion‐weighted MRI signal intensity and localization of infarcts seen on post‐mortem histopathology. © 1991 Academic Press. Inc.
1H and 31P NMR and HPLC studies of mouse L1210 Leukemia cell extracts: The effect of Au(I) and Cu(I) diphosphine complexes on the cell metabolism
Authors: Berners‐Price Susan J. , Sant Melissa E. , Christopherson Richard I. , Kuchel Philip W. 
Published: March 2007

AbstractThe effect of the antitumor complex [Au(dppe)2]Cl (where dppe is Ph2P(CH2)2PPh2) on the overall metabolism of cultured mouse L1 210 leukemia cells was investigated by comparing 1H and 31P NMR spectra of perchloric acid extracts of cells incubated for 1 h in the presence and absence of 2 μm [Au(dppe)2]Cl. There were marked (ca. two‐fold) increases in the levels of lactate and almost all detectable amino acids suggesting a drug‐induced increase in the rate of glycolysis and inhibition of protein synthesis. The levels of taurine and phosphorylcholine were significantly decreased and 31P NMR spectra revealed a depletion of nucleoside triphosphates (NTP). The effect on nucleotide metabolism was investigated further by separating purine and pyrimidine nucleotides and precursors by anion‐exchange HPLC. NTP levels were depleted by ca. 70–90% and there was a ca. three‐to four‐fold increase in nucleoside di‐ and monophosphates. The effect is postulated to be the result of uncoupling of mitochondrial oxidative phosphorylation. The Cu(I) complex [Cu(Ph2PCH‐CHPPh2)2]Cl produced a similar effect on the cellular metabolism but was more potent. The water‐soluble complex [CU(Ph2P(CH2)PEt2)2]Cl caused the accumulation of cellular amino acids at a concentration that did not significantly deplete ATP levels. © 1991 Academic Press. Inc.
In vivo proton metabolite maps using the MESA 3D technique
Authors: Lampman David A. , Murdoch James B. , Paley Martyn 
Published: March 2007

AbstractIn vivo proton spectroscopy requires excellent static magnetic field homogeneity in order to allow suppression of the water signal. This is usually accomplished by restricting the observed signal to a small volume element, or voxel. However, the disadvantage of all single‐voxel techniques is that each experiment results in a spectrum from only a single small region of the patient. This makes it difficult to map metabolite concentrations over extended regions of the patient's anatomy. Standard phase‐encoding techniques that cover the entire sensitive volume of the receiver coil can provide metabolite maps but suffer from excessive field inhomogeneity and/or susceptibility problems at interfaces. We report here on a technique which localizes a large voxel within the patient and uses phase encoding within this voxel to obtain metabolite maps over an extended region of the patient's anatomy. Phantom results are presented to demonstrate the performance of the technique. In vivo results on human brains are also presented. © 1991 Academic Press. Inc.
Iteration of hybridoma growth and productivity in hollow fiber bioreactors using 31P NMR
Authors: Gillies Robert J. , Scherer Peter G. , Rachunand Natarajan , Okerlund Linda S. , Martinez‐Zacuilan Raul , Hesterberg Lyndall , Dale Bruce E. 
Published: March 2007

AbstractApplications of nuclear magnetic resonance (NMR) spectroscopy to isolated or cultured mammalian cells have been limited because of technical difficulties in maintaining cultures at the extremely high densities required by NMR. Among the well‐engineered systems available for such analyses, hollow fiber bioreactors (HFBRs) can maintain the greatest cell density. This attribute of HFBRs makes them ideal for application to NMR‐based studies. These systems are currently being applied in biotechnology, where they are used for the production of mammalian cell‐derived products, such as monoclonal antibodies. In this paper, the application of a HFBR system designed especially for NMR‐based investigations is described. Performance of this system is monitored by NMR and the resulting stability and density of hybridoma cultures are reported. The resulting signal‐to‐noise per unit time is the highest seen to date for a mammalian cell system. © 1991 Academic Press. Inc.