bluuebunny/crossref_metadata_2025 huggingface dataset:
NMR studies in experimental allergic encephalomyelitis: Factors which contribute to T1 and T2 values
Authors: Karlik S. J. , Gilbert J. J. , Wong C. , Vandervoort M. K. , Noseworthy J. H.
Published: March 2007

To determine the factors which may alter NMR relaxation times in multiple sclerosis (MS) lesions we measured the proton T1 and T2, specific gravity (SG), and histology in the central nervous system (CNS; 13–19 levels per animal) in the myelin basic protein (MBP) and CNS‐induced acute and relapsing EAE models in 44 juvenile Hartley guinea pigs. In the MBP model, T1 is unchanged but T2 is prolonged before symptoms and pathological changes occur. T2 remains prolonged during the acute phase of MBP‐in‐duced EAE. In the acute CNS model, T1 and T2 were not different from control despite advanced pathological changes of inflammation and demyelination and changes in specific gravity, indicating a marked change in tissue water content. No single variable, pathological or SG, could predict TI or T2 values in the CNS‐induced model. In active disease in the MBP model, when edema occurs in the presence or absence of parenchymal infiltration, T2 values are increased. However, as the factors which influence tissue NMR characteristics are complex in these MS models, it is likely difficult to infer specific pathological events from MRI findings in patients with MS. © 1990 Academic Press, Inc.
Oxygenation‐sensitive contrast in magnetic resonance image of rodent brain at high magnetic fields
Authors: Ogawa Seiji , Lee Tso‐Ming , Nayak Asha S. , Glynn Paul
Published: March 2007

At high magnetic fields (7 and 8.4 T), water proton magnetic resonance images of brains of live mice and rats under pentobarbital anesthetization have been measured by a gradient echo pulse sequence with a spatial resolution of 65 × 65‐μm pixel size and 700‐μm slice thickness. The contrast in these images depicts anatomical details of the brain by numerous dark lines of various sizes. These lines are absent in the image taken by the usual spin echo sequence. They represent the blood vessels in the image slice and appear when the deoxyhemoglobin content in the red cells increases. This contrast is most pronounced in an anoxy brain but not present in a brain with diamagnetic oxy or carbon monoxide hemoglobin. The local field induced by the magnetic susceptibility change in the blood due to the paramagnetic deoxyhemoglobin causes the intra voxel dephasing of the water signals of the blood and the surrounding tissue. This oxygena‐tion‐dependent contrast is appreciable in high field images with high spatial resolution. © 1990 Academic Press, Inc.
Tm(DOTP)5−: A 23Na+ shift agent for perfused rat hearts
Authors: Buster Douglas C. , Castro M. Margarida C. A. , Geraldes Carlos F. G. C. , Malloy Craig R. , Sherry A. Dean , Siemers Timothy C.
Published: March 2007

Tm(DOTP)5−, the thulium(III) complex of 1,4,7,10‐tetraazacyclododecane N,N′,N″,N‴tetra(methylenephosphonate), is introduced as a 23Na1 shift agent for use in discrimination of the NMR resonances of intra‐ and extracellular 23Na+ ions in perfused rat hearts. The novel shift agent is directly compared to the widely used Dy(TTHA)3‐ (dysprosium(III) triethylenetetraminehexaacetate). © 1990 Academic Press, Inc.
Influence of global ischemia on intracellular sodium in the perfused rat heart
Authors: Malloy Craig R. , Buster Douglas C. , Margarida Castro M. C. A. , Geraldes Carlos F. G. C. , Jeffrey F. Mark H. , Sherry A. Dean
Published: March 2007

Intracellular [Na+], [H+], and [ATP] and mechanical performance were measured in the isovolumic perfused rat heart during ischemia. The concentration of intracellular sodium, [Na+]i, was determined by atomic absorption spectroscopy under control conditions, and [Na+] was monitored by 23Na NMR spectroscopy at 1‐min intervals under control conditions and during global ischemia. [ATP], [H+], and [Pi] were measured by 31PNMR in a separate group under identical conditions. The control [Na+]i measured by atomic absorption was 30.7 ± 3.3 mM(mean ± SD, n = 6), and [Na+]i measured by NMR was 6.2 ± 0.5 mM(n = 3). Brief ischemia (10 min) was associated with a 54% increase in [Na+]i which reversed completely with reperfusion. Developed pressure also returned to control values upon reperfusion. Prolonged ischemia (30 min) produced continuous further accumulation of sodium (0.53 mM/min, r2 = 0.99). [H+] also increased approximately linearly early in ischemia (0.084 μM/min, r2 = 0.97). The rate of increase in [Na+]i was more than 4000 times greater than the increase in [H+] on a molar basis. Nevertheless, [H+]/[Na+] increased early in ischemia because the proportional change in [H+] was greater than that in [Na+] i. These results indicate that (1) intracellular sodium measured by NMR in the functioning heart is about 20% of total intracellular sodium; (2) intracellular acidosis and accumulation of sodium develop simultaneously during global ischemia; (3) increased intracellular sodium content is not in itself an indicator of irreversible injury; and (4) recovery of mechanical performance is associated with return of [Na+] (measured by NMR) to baseline after brief ischemia. The mechanism of the increase in sodium content detected by NMR is unknown. © 1990 Academic Press, Inc.
Measurement of cerebral blood flow in rat brain by 19F‐NMR detection of trifluoromethane washout
Authors: Detre John A. , Eskey Clifford J. , Koretskyp Alan P.
Published: March 2007

The washout of trifluoromethane (CHF3) from rat cerebral cortex was monitored by 19F NMR. After 15 min of inhalation of 67% CHF3/33% O2 the fluorine signal detected was in a steady state. The CHF3 was switched off rapidly at the endotracheal tube and the washout detected with 12‐s time resolution. Two models were used to extract flow information, a simple exponential fit and a model which accounts for arterial CHF3 recirculation. In both cases, a two‐compartment model fit the data significantly better than a one‐compartment model. In both models, the faster time component varied with increasing pCO2, but no significant change in the slow component was detected. At control values of pCO2, there was a small difference in washout rate constants derived from the two models. At high pCO2, when tissue washout was comparable to arterial washout of CHF3, the model which accounted for arterial recirculation gave higher flows. Using this two‐compartment model with correction for recirculation, a control flow (pCO2 = 35 mm Hg) of 0.73 ± 0.04 ml/min/g was measured. Increasing plasma pCO2 increased the apparent flow six‐ to sevenfold with a 4.4% increase in flow per millimeter of Hg change in CO2. These results are qualitatively in agreement with results found by others using the washout of 133Xe. However, this method yields values for flow that are lower than those obtained using 133Xe washout, probably because of diffusion limitations of CHF3. © 1990 Academic Press, Inc.
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

This 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

In 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

Two‐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

Paramagnetic 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

In 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

In 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

The 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

The 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

Proton 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

Volume‐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

Recently 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

The 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

In 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

We 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

Multiple 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

Linear 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

The 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

The 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

In 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

Applications 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.
Human brain proton localized NMR spectroscopy in multiple sclerosis
Authors: Van Hecke P. , Marchal G. , Johannik K. , Demaerel P. , Wilms G. , Carton H. , Baert A. L.
Published: March 2007

Localized proton spectroscopy of the brain was performed on MS patients (n = 18) and the results are compared with those of a control group (n = 17). The experiments were performed in a 1.5‐T Siemens Magnetom using the stimulated echo method and selective water suppression. Acquisition parameters were TR/TE/TM = 3000/270/30 ms, NA = 256, and Acq = 13 min. Localized volumes ranged from 8 to about 80 cc. The patients (ages 25 to 66) were at various stages of the disease. Three of the eighteen patients did not show any plaques on the MR images. VOIs were chosen to contain as much plaque volume as possible in the cerebrum white matter. In the controls and in the patients with no plaques, the VOI were localized in similar white matter regions. All spectra were characterized by the presence of Cho (3.2 ppm), PCr + Cr (3.0 ppm), and NAA (2.0 ppm). The ratios NAA/Cho and NAA/(PCr + Cr) were calculated for both the MS and the control group. The results for the three MS patients with no detectable plaques did not differ significantly from the results of the control group. The former group is, however, too limited to draw any conclusion for the moment. For the MRI positive patients, the following values were found (means ± 1 SD): NAA/Cho = 1.98 ± 0.33 and NAA/(PCr + Cr) = 2.16 ± 0.14. In the normals, these values were NAA/Cho = 2.54 ± 0.39 and NAA/(PCr + Cr) = 2.76 ± 0.25. The results quoted are TR and TE dependent. It is concluded that these ratios are significantly lower in the MS patients (p < 0.001). The decrease is attributed to a decrease in the NAA peak intensity. This is supported by the fact that the NAA/Cho and the NAA/Cr ratios are reduced by the same amount (0.78) in the MS patients. Also, this decrease in metabolite ratios is not significantly affected by the MS plaque density and the stage and duration of the disease. © 1991 Academic Press. Inc.
Multiple inversion recovery reduces static tissue signal in angiograms
Authors: Dixon W. Thomas , Sardashti Maziar , Castillo Mauricio , Stomp Guido P.
Published: March 2007

Spin label angiography compares two images by subtraction. The first is obtained after blood in one region is labeled by inversion and flows into a region of interest. Labeling is not used for the second image, so only labeled blood remains in the final angiogram after subtraction. This subtraction is never perfect, but with starting images containing less static tissue signal, the remaining background can be reduced. This can be achieved by observing at the zero crossing following an inversion. Multiple inversions allow one to null the signal from tissues with differing T1 simultaneously. We present equations and sample calculations for inversion times and demonstrate the resistance to subject motions (peristalsis, breathing, speaking) resulting from two inversions. Adequate suppression of static tissue signal allows one to dispense with labeling and subtraction, halving the minimum time needed to acquire an image. © 1991 Academic Press. Inc.
Direct projective time‐of‐flight NMR angiography within 4 s
Authors: Matsuda Tetsuya , Doyle Mark , Pohost Gerald M.
Published: March 2007

To enhance contrast between flow and static tissue, NMR projective angiographic methods usually require data subtraction, or alternatively the application of special data processing routines such as the “maximum intensity projection” algorithm. We have successfully developed a direct projection method which yields sufficient flow/static contrast in a single acquisition, producing angiograms in under 4 s. Direct projection angiograms of the cervical and abdominal vessels were obtained. The cervical vessels were uniformly depicted in a number of different projection views. The abdominal vessels exhibit intensity variations due to the pulsatile flow pattern. A series of abdominal angiograms were acquired, each triggered at a different starting cardiac phase. When displayed as a movie sequence the pulsatile flow pattern was seen to advance along the arteries. To more uniformly represent the abdominal vessels a 24‐s average was adequate. This new technique should allow NMR angiograms to be obtained in a “fluoroscopic” mode. © 1991 Academic Press. Inc.
Analysis of the higher‐order echoes in SSFP
Authors: Kim D. J. , Cho Z. H.
Published: March 2007

In the steady‐state free precession (SSFP) with an applied linear gradient, the transverse magnetizations are periodically distributed. Fourier analysis of this periodic distribution leads to the understanding of many interesting phenomena in SSFP. It is found that there are many other higher‐order echoes in SSFP in addition to the previously known echoes. By deriving general description of the transverse magnetization of SSFP and by expanding the echo time independent term with Fourier series, the higher‐order echoes including the two previously known FISP and CE‐FAST are understood and explained. These higher‐order echoes are studied in detail by both computer simulation and experiments and their results are reported. © 1991 Academic Press, Inc.
In vivo monitoring of changes in 5‐fluorouracil metabolism induced by methotrexate measured by 19F NMR spectroscopy
Authors: Koutcher Jason A. , Sawyer Robert C. , Kornblith Alice B. , Stolfi Robert L. , Martin Daniel S. , Devitt Mary L. , Cowburn David , Young Charles W.
Published: March 2007

We have used in vivo 19F NMR spectroscopy to study the metabolism of 5‐fluorouracil (FUra) in tumors with and without pretreatment with methotrexate (MTX). Using the CD8F1 murine mammary tumor as an in vivo model, we observed signals from FUra, α‐fluoro‐β‐alanine (FβALA), α‐fluoro‐β‐ureidopropionic acid (FUPA), and 5‐fluorouracil‐nucleotides (FUN) after intravenous or intraperitoneal injection of 150 mg/kg FUra. Formation of FUN was increased about 1.7‐fold in CD8F1 tumor with methotrexate pretreatment as determined by acid extraction and HPLC analysis. A comparison of in vivo NMR spectra from FUra and sequential MTX + FUra‐treated tumors showed a significantly higher ratio of the FUN signal to the initial total 19F signal in the MTX + FUra‐treated tumors (p < 0.001) for animals receiving FUra either intravenously or intraperi‐toneally. In addition, tumors treated with MTX + FUra had significantly longer time durations during which FUN was detected, independent of the mode of administration. These experiments indicate that in vivo 19F NMR spectroscopy can be used to noninvasively monitor alterations of 5‐fluorouracil metabolism that occur with administration of modulating agents such as methotrexate. Further studies, in both murine tumor models and patients, are indicated to determine if these results can be correlated with tumor response. © 1991 Academic Press, Inc.
NMR measurements of different tissue perfusion parameters
Authors: Dixon W. Thomas
Published: March 2007

The traditional perfusion rate is based on the amount of fluid flowing longitudinally down the capillaries, often given in ml/100 g tissue/min. In principle, fluid flowing radially out of or into the capillaries can be measured as well. Radial and longitudinal perfusion have the same units but independent values. If spins leave and reenter a capillary several times during a transit, radial perfusion can exceed longitudinal perfusion and it probably does. Radial perfusion measures capillary wall function. Progressively increasing the time between two gradient pulses in a proposed radial perfusion imaging sequence allows more magnetization to move into the vasculature to be dephased or removed. Progressive decreases in gradient strength keep diffusion effects constant allowing isolation of the desired perfusion effects. © 1991 Academic Press, Inc.
Intravoxel incoherent motion imaging using spin echoes
Authors: Le Bihan Denis , Turner Robert
Published: March 2007

The purpose of this paper is to review the basic principles of diffusion measurement with spin echoes. These principles can be combined with those of MR imaging to generate maps of diffusion coefficients. Diffusion imaging can be extended to imaging of other intravoxel incoherent motions (IVIM), such as blood microcirculation. Some of the technical problems encountered when implementing IVIM imaging are presented. © 1991 Academic Press, Inc.
Diffusion/perfusion MR imaging of acute cerebral ischemia
Authors: Kucharczyk John , Mintorovitch Jan , Asgari Haleh S. , Moseley Michael
Published: March 2007

In vivo echo‐planar MR imaging was used to measure apparent diffusion coefficients (ADC) of cerebral tissues in a comprehensive noninvasive evaluation of early ischemic brain damage induced by occlusion of the middle cerebral artery (MCA) in a cat model of acute regional stroke. Within 10 min after arterial occlusion, ADC was significantly lower in tissues within the vascular territory of the occluded MCA than in normally perfused tissues in the contralateral hemisphere. Sequential echo‐planar imaging was then used in conjunction with bolus injections of the magnetic susceptibility contrast agent, dysprosium DTPA‐BMA, to characterize the underlying cerebrovascular perfusion deficits. Normally perfused regions of brain were identified by a dose‐dependent 35–70% loss of signal intensity within 6–8 s of contrast administration, whereas ischemic regions appeared relatively hyperintense. These data indicate that sequential diffusion/perfusion imaging may be diagnostically useful in differentiating permanently damaged from reversibly ischemic brain tissue. © 1991 Academic Press, Inc.
In Vitro proton spectroscopy of normal and abnormal prostate
Authors: Yacoe Marshall E. , Sommer Graham , Peehl Donna
Published: March 2007

Previous biochemical and 13C NMR spectroscopic data have suggested that the metabolism of citrate, a secretory product of normal prostate, may be interrupted in prostate cancer. In the present study in vitro 1H NMR spectroscopy was used to see if cell strains derived from prostate cancers could be reliably distinguished from those of normal prostate epithelium. High‐resolution one‐dimensional and two‐dimensional J‐resolved 1H NMR spectra as well as gas chromatography coupled with mass spectroscopy were used to study extracts of highly defined cell strains from normal peripheral zone, normal central zone, adenocarcinoma, and benign prostatic hyperplasia. Resonances assigned to citric acid and related metabolites were identified. Cell strains derived from prostate cancers tended to have smaller amounts of citrate than those from normal prostate epithelium. However, the differences were small and not statistically significant. The lack of statistically significant differences may reflect the variability present in both normal and abnormal cell strains and thus underscore the well‐known difficulty in differentiating normal and cancerous tissues. © 1991 Academic Press, Inc.
Localized 1H NMR spectroscopy in Canavan's Disease: A report of two cases
Authors: Austin S. J. , Connelly A. , Gadian D. G. , Benton J. S. , Brett E. M.
Published: March 2007

Two children with Canavan's Disease, an autosomal recessive leukodystrophy, were studied by localized 1H spectroscopy. The N‐acetylaspartate (NAA) signal intensity was high relative to other metabolite signals, and the signal intensity from choline‐containing compounds was low. These findings are discussed in relation to a possible role for NAA in normal myelination. © 1991 Academic Press, Inc.
Dextran magnetite as a liver contrast agent
Authors: Magin R. L. , Bacic G. , Niesman M. R. , Alameda J. C. , Wright S. M. , Swartz H. M.
Published: March 2007

The superparamagnetic particle dextran magnetite was studied as a liver tumor contrast agent for magnetic resonance imaging (MRI). The effects of dextran magnetite on the longitudinal (T1) and transverse (T2) relaxation times in liver, spleen, and an implanted rat liver tumor were measured at 0.47 T (IBM/Bruker PC‐20 relaxometer) over the dose range of 23 to 69 μmol Fe/kg. Dextran magnetite substantially reduced the T2 of the liver and spleen, but not of the tumor, thereby providing a basis for improved tumor imaging. The T1 of the tumor was not affected following injection of dextran magnetite in the dose range studied, while the spleen T1 was reduced substantially more than the T1 of the liver. Histological studies using the iron reaction for Prussian blue clearly showed dextran magnetite in the liver and spleen, but not in the tumor. While dextran magnetite was sequestered in macrophages in both liver and spleen, the distribution in the liver was more diffuse (70 μm average particle separation) than that in the spleen (25 μm separation). The lack of a T1 effect in the liver is consistent with the fact that a majority of the water in the tissue cannot diffuse to the relaxational centers on the time scale of the liver's intrinsic T1 (280 ms). In the spleen, however, the dextran magnetite is more densely packed in the red pulp allowing a significant fraction of the water to be relaxed by a T1 mechanism. Spin‐echo images of the implanted tumor (mammary adenocarcinoma, R3230AC) in the livers of Fischer 344 rats were obtained at 0.50 T (Siemens Magnetom). The tumor‐to‐liver contrast was improved for both T1 and T2‐weighted spin‐echo images after intravenous injection of the dextran magnetite contrast agent. The contrast determined from these images agreed with that predicted by the measured T1 and the T2 (Hahn spin‐echo) values. In addition, gradient‐echo T2‐weighted images with good contrast were obtained in a much shorter imaging time than was needed for T2‐weighted spin‐echo images. These results demonstrate that the MRI contrast enhancement observed with dextran magnetite is based on its selective uptake and distribution in the macrophages in the liver and spleen and that this agent has substantial potential as a superparamagnetic MR contrast agent. © 1991 Academic Press, Inc.
Pre‐ and postmortem diffusion coefficients in rat neural and muscle tissues
Authors: Macfall J. R. , Maki J. H. , Johnson G. A. , Hedlund L. W. , Cofer G. P.
Published: March 2007

Pulsed gradient diffusion‐weighted spin‐echo images (7 to 11 gradient strengths) were obtained in a coronal slice through the midbrain for five normal adult white rats before and after sacrifice in a 2‐T CSI system with air temperature control. The pulse sequence was cardiac gated and respiratory synchronized in order to minimize motion artifacts (Tr > 2 s, Te ‐ 30 ms). Diffusion coefficients reflecting several tissue compartments (D*) in brain and muscle were calculated and referenced to simultaneously imaged tubes of water. In the living animals, brain cortical matter had a value of D* = (0.82 ± 0.02) × 103 mm2/s, deeper brain regions had a value of D* = (0.73 ± 0.02) × 10‐3 mm2/s, and the muscle had a value of D* = (1.4 ± 0.1) × 103 mm2/s. Postmortem the values in brain dropped by approximately 30%, while remaining constant in muscle. Signal intensity in the spin‐echo images for muscle tissue rose by 50% over a 1‐ to 2‐h interval after sacrifice while that of brain tissue remained relatively stable. © 1991 Academic Press, Inc.
The effects of chronic ethanol consumption on the intact rat liver studied by in vivo31P NMR spectroscopy
Authors: Brauer Manfred , Ling Mingfu
Published: March 2007

In vivo 31P nuclear magnetic resonance (NMR) spectroscopy provides unique opportunities to study the biochemistry of an organ within the intact animal in a totally noninvasive way. We have used in vivo and in vitro 31P NMR spectroscopy to study steady state changes in the major phosphorus‐containing metabolites of the rat liver in control and chronically ethanol‐treated rats. Chronic (4 month) ethanol treatment caused a statistically significant increase in the inorganic phosphate and phosphodiester resonances of rat liver in in vivo 31P NMR spectra relative to pair‐fed control rats. Phosphomonoester and adenosine 5'‐triphosphate resonances, as well as intracellular pH, were not appreciably altered. The effects of chronic ethanol treatment were particularly apparent in the response of the liver to a metabolic challenge of glycerol. Glycerol is phosphorylated almost exclusively in the liver and metabolized predominately via glycolysis and gluconeogenesis. Our in vivo 31P NMR results after administration of glycerol showed a significant increase in the phosphomonoester resonance in the liver of chromic ethanol‐treated rats but not for their pair fed controls. In vitro 31P NMR studies of perchloric acid extracts of liver showed that the increase was due to an accumulation of sn‐glycerol 3‐phosphate. This effect is due to the NAD+ ‐dependent glycerol 3‐phosphate dehydrogenase step being inhibited in the chronic ethanol‐treated rats. This glycerol test may be useful in assessing the ability of the liver to rapidly regenerate NAD+ in situ and may be a more sensitive indicator of redox imbalance than steady state ratios of redox pairs (e. g., lactate /pyruvate). © 1991 Academic Press, Inc.
Temporal and spatial analysis of fields generated by eddy currents in superconducting magnets: Optimization of corrections and quantitative characterization of magnet/gradient systems
Authors: Boesch Ch. , Gruetter R. , Martin E.
Published: March 2007

We propose methods for the spatial and temporal characterization of time‐dependent magnetic fields generated by eddy currents after switching gradients. For an on‐line determination of the temporal variations of the fields, we extract two terms from the unresolved signal of an extended sample, describing the time evolution of a frequency shift γΔBz (t) and of a decay constant k(t). This procedure allows us to optimize interactively the multiexponential pre‐emphasis as well as any spectral volume selection method with respect to eddy currents, Additionally, we suggest an imaging sequence which allows us to determine the spatial distribution of eddy current fields at a chosen time‐point after any gradient sequence to be tested. Expansion of these eddy currents fields into spherical harmonic functions proves the existence of a higher order terms, which cannot be corrected by a standard pre‐emphasis device, where time constants and amplitudes are adjusted on the X, Y, Z and Z0 coils. The proposed numerical analysis gives a tool to characterize any magnet/ gradient system quantitatively with respect to eddy current performance. © 1991 Academic Press, Inc.
Fucose in 1H COSY spectra of plasma membrane fragments shed from human malignant colorectal cells
Authors: Lean Cynthia L. , Mackinnon Wanda B. , Mountford Carolyn E.
Published: March 2007

The methyl‐methine cross peak of bound fucose has been assigned in the COSY spectrum of plasma membrane shed from human malignant colorectal cells. This cross peak (1.33‐4.27 ppm), which is superimposed on the methyl‐methine cross peak of threonine, was assigned following hydrolysis of the sample. Acid hydrolysis led to a 28 ± 5% reduction in the intensity of the cross peak and the apperance of the α and ß forms of fucose. Chemical analysis confirmed the release of free fucose. Lactate anion. which was not perturbed by the hydrolysis, was used as an internal standard. © 1991 Academic Press, Inc.