bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental approaches to image localized human31P NMR spectroscopy
Authors: Luyten Peter R. , Groen Jan P. , Vermeulen Jan W. A. H. , Den Hollander Jan A. 
Published: March 2007

AbstractExperimental procedures for obtaining localized31P NMR spectra of humans by means of the ISIS sequence are discussed in detail. The technique is optimized for use with volume coils and with surface coils in order to measure localized31P NMR spectra ofdifferent tissues and organs. Selective frequency‐modulated (FM) inversion and excitation pulses are applied for optimal inversion or excitation despite B1 inhomogeneity. Pulse imperfection may lead to spurious signal contributions from outside the selected volume; this contamination is reduced by using long pulse intervals, by properly ordering the ISIS acquisitions, and by using FM excitation pulses. Simultaneous measurement of multiple volumes was implemented by including an additional selective inversion pulse, and an extension of the ISIS addition/subtraction scheme. Localized T1 measurements with surface coils are implemented by using a B1‐insensitive inversion pulse in the inversion recovery sequence. The quantitative reproducibility of localized31P NMR spectra was verified. Absolute metabolite concentration can be determined after a suitable calibration of the31P NMR spectrum. Localized shimming is required to obtain localized31P NMR spectra of excellent spectral resolution. This is done by monitoring the1H NMR signal from water by a single‐shot localization technique. The techniques discussed can be applied to obtain spectra of brain, liver, heart, and other organs.31P NMR spectra of intracranial tumors demonstrate its applicability in the examination of patients. © 1989 Academic Press. Inc.
The effect of gadolinium DTPA on tissue water compartments in slow‐ and fast‐twitch rabbit muscles
Authors: Kofi Adzamli I. , Jolesz Ferenc A. , Bleier Alan R. , Mulkern Robert V. , Sandor Tamas 
Published: March 2007

AbstractProton T2 relaxation and its biexponential components have been determined in rabbit skeletal muscle in the presence and absence of GdDTPA. The effect of GdDTPA, which distributes only in the extracellular space, was greatest in the longer‐relaxing T2 component (T22). A 27% reduction in T22was measured for slow‐twitch (red) muscle and 17% for fast‐twitch (white) muscle, consistent with the larger extracellular space of the former. Magnetic resonance images demonstrated apparent contrast between red and white rabbit muscles. This contrast was instantaneously enhanced by administration of GdDTPA and returned to near normal levels after approximately 30 min. These functional changes in tissue contrast are consistent with differences in blood perfusion and biological water compartmentation between fast‐ and slow‐twitch skeletal muscles.
Toxicity of dysprosium shift reagents in the isolated perfused rat kidney
Authors: Endre Z. H. , Allis J. L. , Radda G. K. 
Published: March 2007

AbstractSodium and water spectra were acquired from the isolated perfused rat kidney by using a double‐tuned probe designed to have high X nucleus sensitivity and low 1H sensitivity. Both DyTTHA and DyPPP were used to distinguish intra‐ and extracellular 23Na resonances before and after the onset of hypoxia. Only DyPPP was useful in separating the two compartments, with a maximal chemical shift difference produced at a concentration of 4.5 mM. Both shift reagents were nephrotoxic at concentrations under 5 mM and produced an immediate decrease in renal‐concentrating capacity and increases in fractional sodium and potassium excretion and increased renal vascular resistance. These disturbances of renal physiological parameters were accompanied by progressive broadening of the renal H2O resonance. 1H NMR may be a subtle means of monitoring nephrotoxicity.
The synthesis of soft pulses with a specified frequency response
Authors: Shinnar Meir , Bolinger Lizann , Leigh John S. 
Published: March 2007

AbstractWe propose a new approach to synthesizing shaped pulses, by first synthesizing a hard pulse sequence and then converting it to a soft pulse. In previous papers, we developed a new approach to synthesizing hard pulse sequences by exactly inverting the Bloch equation, which yields the optimal frequency response. These results can now be applied to shaped pulses. Specifically, one can specify (1) the total duration of the pulse, (2) the frequency range it is desired to perturb, (3) the perturbation desired and, (4) the frequency range it is desired not to perturb. One can then synthesize a shaped pulse which has the desired effect with the least possible error. This enables us to obtain very sharp inversion and π/2 pulses. © 1989 Academic Press, Inc.
In Vivo 31P and 1H NMR studies of rat brain tumor pH and blood flow during acute hyperglycemia: Differential effects between subcutaneous and intracerebral locations
Authors: Ross Brian D. , Mitchell Steven L. , Merkle Hellmut , Garwood Michael 
Published: March 2007

AbstractSurface coil NMR spectroscopy was used to monitor the hyperglycemia‐induced alterations in pH and blood flow in vivo in C6 gliomas implanted both subcutaneously and intracerebrally in rats. Tumor pH was calculated from the chemical shift difference between PCr and Pi in the 31P NMR spectra. Subcutaneous glioma pH decreased 0.8 units by 1 h after intraperitoneal administration of an aqueous 50% glucose solution (6 g glucose per kg body weight). In contrast, hyperglycemia failed to significantly alter the pH of intracerebral gliomas which were monitored for 90 min following administration of glucose. Tumor blood flow (TBF) was determined both pre‐ and post‐glucose administration using deuterium NMR by monitoring the time course of D2O washout following intratumoral injection of saline D2O. Subcutaneous and intracerebral TBF were found to have an average change of‐78.1 % (range ‐47.4 to ‐93.3%, n = 5) and ‐21.1% (range +6.0 to ‐37.8%, n = 9), respectively. In addition, laser Doppler blood flow measurements of rat skin and subcutaneous glioma revealed a dramatic reduction in blood flow in both tissues following glucose administration. These results indicate that the effects of acute hyperglycemia are site dependent and that hyperglycemia alone is not beneficial for inducing intracellular acidosis in intracerebral tumors. © 1989 Academic Press, Inc.
Effect of inotropic stimulation on cytosolic mg2+ in isolated rat heart: a 31p magnetic resonance study
Authors: Headrick John P , Willis Roger J. 
Published: March 2007

AbstractAlterations in cytosolic metabolites and [Mg2+], were monitored using 31P magnetic resonance spectroscopy during inotropic stimulation of isolated rat heart [10 n M isoproterenol, 0.6 μM isobutyl‐1‐methylxanthine (IBMX), 5 μM ouabain]. All drugs significantly elevated contractile function (rate‐pressure product) and MVO2 by approximately 100‐150% (P 0.001), decreased cytosolic [creatine phosphate] ([CrP]) and [ATP] (approximately 65 and 80% of control values, respectively) (P 0.001), increased [ Pi ] to more than 180% of pretreatment values, and decreased [ H+] by less than 15% (P 0.05). A significant relative shift in the α‐P and β‐P resonances of ATP (P 0.01) occurred with inotropic stimulation. [Mg2+], calculated on the basis of these shifts was found to be 0.78 ± 0.1 mM in control hearts, and increased to maxima of 1.9 ± 0.2,2.0 ±0.2, and 2.9 ± 0.2 m M during infusion of isoproterenol, IBMX, and ouabain, respectively. Changes in [Mg2+], correlate with cytosolic [ATP] + [CrP] in all hearts (r = 0.89, 0.91, and 0.88 in isoproterenol‐, IBMX‐, and ouabain‐treated hearts, respectively). The significantly higher [Mg2+], with ouabain infusion (P 0.01) at similar workloads and [ATP] + [CrP] supports the proposal that a ouabain‐inhibited Mg2+ pump exists in the plasma membrane. The data support acute changes in [ Mg2+ ]i during alterations in inotropic state that may be important in modulating metabolic and contractile function. © 1989 Academic Press, Inc.
Environmental optimization and shielding for nmr experiments and imaging in the earth's magnetic field
Authors: Favre B. , Bonhe J. P. , Mehier H. , Peyrin J. O. 
Published: March 2007

AbstractFor many years, a number of laboratories have been working on the applications of very low field NMR. In 1985, our laboratory presented the first NMR images using the earth's magnetic field. However, the use of this technique was limited by the weakness of the signal and the disturbing effects of the environment on the signal‐to‐noise ratio and on the homogeneity of the static magnetic field. Therefore experiments had to be performed in places with low environmental disturbances, such as open country or large parks. In 1986, we installed a new station in Lyon, in the town's hostile environment. Good NMR signals can now be obtained (with a signal‐to‐noise ratio better than 200 and a time constant T*2 better than 3 s for 200‐ml water samples and at a temperature of about 40°C). We report here our new technique: A shielded box was built and installed on scaffoldings above the terrace roof of our faculty building. Gradient coils were used to correct the local inhomogeneities of the earth's magnetic field. We show FIDs and MR images of water‐filled tubes made with or without these improvements.
Parameter estimation for in vivo magnetic resonance spectroscopy (mrs) using simulated annealing
Authors: Sekihara K. , Ohyama N. 
Published: March 2007

AbstractA method for estimating the spectral parameters from a noisy FID is proposed. The method uses a priori information concerning the lower and upper limits between which such parameters' values can exist. Computer simulation results show that, using the proposed method, values of the spectral parameters can be accurately estimated from a noisy FID.
Efficient remote transmission line probe tuning
Authors: Rath Alan R. 
Published: March 2007

AbstractAn approach is described which allows remote tuning of a probe via a length of transmission line, while retaining nearly ideal efficiency relative to the equivalent locally tuned coil. This preservation of efficiency is accomplished through the principle of “partial local matching.” In comparison to common methods of remote tuning which involve half‐wavelength cables, or in which a length of transmission line is itself utilized as a tuning element, the partial matching method results in a substantial increase in the efficiency of power transfer to the coil, and therefore increased B1 field intensity and signal‐to‐noise ratio. Applications in which the use of local variable tuning capacitors is made difficult by either space, accessibility, or environmental considerations should benefit from this method.
Inversion‐recovery echo‐planar imaging (ir‐epi) at 0.5 T
Authors: Stehling M. K. , Ordidge R. J. , Coxon R. , Mansfield P. 
Published: March 2007

AbstractEcho‐planar imaging is used in combination with a spin preparation phase to produce a T1‐weighted image. The small additional time penalty in this procedure does not detract significantly from the ultrahigh‐speed imaging capability of EPI, allowing a rapid real‐time optimization of tissue parameters in the image display. Results obtained on a head demonstrate this technique. © 1990 Academic Press, Inc.
Measurement of tissue blood flow using intravascular relaxation agents and resonance imaging
Authors: Gore John C. , Majumdar Sharmila 
Published: March 2007

AbstractSimple concepts of indicator‐dilution techniques are described, and the theoretical basis of measuring regional blood flow via transit time measurements of a blood pool marker is discussed. Using very fast imaging of the effects of an appropriate and efficient relaxation agent, the concentration‐time curve of the agent can be quantified. Preliminary measurements of the transit of superparamagnetic iron oxide through a rat brain at 2.0 T have been obtained. There are problems, however, in relating the NMR signal change to the tissue concentration of an intra vascular relaxation agent when there is not fast exchange of the tissue water with the water in the vasculature, or when the precise efficacy of the agent varies with the geometrical arrangement of the capillaries. Studies of the effects of superparamagnetic iron oxide particles in different media confirm that the in vivo efficacy varies among different tissues, which complicates their use as blood flow markers. © 1990 Academic Press, Inc.
Compatibility of the two‐site exchange model and 1H NMR relaxation rates
Authors: Mulkern R. V. , Bleier A. R. , Sandor T. , Jolesz F. A. 
Published: March 2007

AbstractWe demonstrate a formalism for determining whether 1H longitudinal and transverse magnetic relaxation decay curves are compatible with a model of proton exchange between two sites with inherently different relaxation rates. We apply the method to published data in which both decay curves have been fit to normalized biexponential functions, a prediction of the simplest two‐site exchange model. The analysis is applied to relaxation data of adsorbed water vapor on silica gel (J. R. Zimmerman and J. A. Lasater, J‐ Phys. Chem. 62, 1157 (1958)) and to relaxation data reported in mycelia of Botrytis cinerea Persoon and pupae of the tobacco cutworm (M. Yoshida and K. Nose, Agric. Biol. Chem. 51, 3399 (1987)). Exchange parameters are calculated form these data sets and the compatibility of the two‐site exchange model with the data is discussed for each case. The sensitivity of the calculated exchange parameters to errors in the biexponential fitting parameters is treated in some detail. © 1990 Academic Press, Inc.
Measurement of translational displacement probabilities by NMR: An indicator of compartmentation
Authors: Cory D. G. 
Published: March 2007

AbstractWe introduce and demonstrate an NMR pulsed gradient stimulated echo method of directly obtaining the molecular translational displacement probability (displacement profile) of a liquid. The temporal development of the displacement profile reflects the presence of diffusion, restrictions to diffusion (e.g., walls, membranes), flow, and spatially dependent relaxation sinks. This approach allows the study of compartments which are too small to be observed by conventional NMR imaging methods. The distribution of spatial properties of compartments can be characterized over a spatial field of about 0.1 to 25 μm, completely independent of the absolute spatial location of the individual compartments. © 1990 Academic Press, Inc.
Proton‐enhanced 13C imaging/spectroscopy by polarization transfer
Authors: Swanson Scott D. , Quint Leslie E. , Yeung Hong N. 
Published: March 2007

AbstractCarbon‐13 magnetic resonance imaging/spectroscopy (CMRI/S) was performed using polarization transfer techniques where sensitivity of the carbon signal was enhanced by transferring the proton spin order to the carbon nuclei. The experimental feasibility of using polarization transfer techniques at 2.0 T was demonstrated with a phantom and an intact chicken egg. The potential clinical applications of CMRI/S with polarization transfer include the assessment of prostate cancer. Preliminary results using human prostate specimens are presented. © 1990 Academic Press, Inc.
T2 of endotoxin lung injury with and without methylprednisolone treatment
Authors: Shioya Sumie , Haida Munetaka , Tsuji Chizuko , Ono Yoshiaki , Miyairi Akira , Fukuzaki Minoru , Ohta Yasuyo , Yamabayashi Hajime 
Published: March 2007

AbstractNMR relaxation times (T1 and T2) and the water content (WC) of in vitro rat lungs were measured during the course of endotoxin lung injury in rats. Measurements of normal lungs, untreated endotoxin‐injured lungs, and endotoxin‐injured lungs treated with methylprednisolone (MPSL) were compared. The untreated endotoxin lungs showed prolongation of the fast and slow T2 components (T2r and T2s), but no significant changes in T1 or water content. Also, there was no correlation between 1 /WC and relaxation rates or between T1 and T2. MPSL treatment prevented T 2f and T2s prolongation; however, the duration of MPSL effectiveness was limited. Animals which were treated with MPSL more than 7 h prior to measurements showed T2 prolongation. This study indicates that NMR relaxation times, particularly T2, can be useful in evaluating lung injuries and their treatments. © 1990 Academic Press, Inc.
Echo planar imaging of isolated perfused rat hearts at 4.7 T: A comparison of Langendorff and working heart preparations
Authors: Blackband S. J. , Chatham J. C. , O'Delland W. , Day S. 
Published: March 2007

AbstractThe implementation of echo planar imaging at 4.7 T is demonstrated using a home‐built gradient and radiofrequency assembly. The application of such a technique to the study of the isolated perfused rat heart is demonstrated. Langendorff and working heart perfusion preparations are compared and changes in the left ventricular volume shown are to be much larger in the working heart preparation. Such a methodology is expected to provide a useful model for the study of cardiac function and dynamics in the normal and diseased states under controlled perfusion conditions. © 1990 Academic Press, Inc.
Application of interlaced orientation slices in orthogonal planes for system characterization and as a basis for standardized brain sections in multiple‐oblique positions
Authors: Boesch Ch. , Martin E. 
Published: March 2007

AbstractInterlaced acquisition of orthogonal spin‐echo orientation slices yields saturated intersection lines, which are available for a system characterization (spatial distortions, slice thickness, chemical shift displacement). Additionally, these scout images contain complete information for a transformation of the gradient coordinate system into the oblique coordinate system of the patient, bearing standardized planes for improved image interpretation and quantitative examinations. © 1990 Academic Press, Inc.
Rapid radiofrequency calibration in MRI
Authors: Carlson J. W. , Kramer D. M. 
Published: March 2007

AbstractA collection of modified procedures for setting rf transmitter levels using a three‐pulse sequence is described. Based on a geometrically weighted ratio of four signals, an estimate of the flip angle is calculated and used for an updating prescription. These techniques are designed to perform rapidly yet eschew systematic errors due to relaxation during the pulse sequence. © 1990 Academic Press, Inc.
Proton spectral editing in the inhomogeneous radiofrequency field of a surface coil using modified stimulated echoes
Authors: Lahrech Hana , Briguet Andre 
Published: March 2007

AbstractIt is shown that the modified stimulated echo sequence, [θ](±x±y)−t1−[θ](+x)−t2/2−[2θ](+x)−t2/2−[θ](+x)−t1−Acq(±x ∓ y), denoted as MSTE[2θ]x according to the exciter phase of the 2θ pulse, is able to perform proton spectral editing without difference spectra. On the other hand, this sequence appears to be suitable for spatial localization. Sensitivity and spatial selectivity of MSTE and conventional stimulated echo sequence (STE) are briefly compared. MSTE is applied to editing lactate in the rat brain using the locally restricted excitation of a surface coil. © 1990 Academic Press, Inc.
Development of a micromanometer‐tip catheter to record high‐fidelity pressures during cine‐gated NMR without significant image distortion
Authors: Dell'italia Louis J. , Carter Bruce , Millar Huntly , Pohost Gerald M. 
Published: March 2007

AbstractWe report a new micromanometer‐tip catheter to record high‐fidelity pressures during cine‐gated gradient echo NMR imaging in an intact animal model. Of the various metals and alloys tested for use in its construction, brass produced the smallest NMR artifact with minimal magnification. With the use of this new catheter design, there was little signal loss and no distortion of endocardial borders during imaging. © 1991 Academic Press, Inc.
Quantitative measurement of tissue perfusion and diffusion in vivo
Authors: Chenevert Thomas L. , Pipe James G. , Williams David M. , Brunberg James A. 
Published: March 2007

AbstractMagnetic resonance imaging techniques designed for sensitivity to microscopic motions of water diffusion and blood flow in the capillary network are also exceptionally sensitive to bulk motion properties of the tissue, which may lead to contrast artifact and large quantitative errors. The magnitude of bulk motion error that exists in human brain perfusion/diffusion imaging and the inability of cardiac gating to adequately control this motion are demonstrated by direct measurement of phase stability of voxels localized in the brain. Two methods are introduced to reduce bulk motion phase error. The first, a postprocessing phase correction algorithm, reduces coarse phase error but is inadequate by itself for quantitative perfusion/diffusion MRI. The second method employs orthogonal slice selection gradients to define a column of tissue in the object, from which echoes may be combined in a phase‐insensitive manner to measure more reliably the targeted signal attenuation. Applying this acquisition technique and a simplistic model of perfusion and diffusion signal attenuations yields an estimated perfusion fraction of 3.4 ± 1.1% and diffusion coefficient of 1.1 ± 0.2 × 10−5 cm2/s in the white matter of one normal volunteer. Successful separation of perfusion and diffusion effects by this technique is supported in a dynamic study of calf muscle. Periods of normal blood flow, low flow, and reactive hyperemia are clearly distinguished in the quantitative perfusion results, whereas measured diffusion remained nearly constant. © 1991 Academic Press, Inc.
Quantitative 1H magnetization transfer imaging in vivo
Authors: Eng John , Ceckler Toni L. , Balaban Robert S. 
Published: March 2007

AbstractA major factor contributing to proton (1H) spin‐lattice relaxation in biological tissues is believed to be magnetization transfer between 'H in free bulk water and 1H in restricted motion associated with macromolecules. We have shown recently that saturation transfer is an effective approach for studying this magnetization transfer process. Herein the determination of magnetization transfer rates in biological tissues is further analyzed by considering the time and power dependencies of saturation transfer. Following these analyses, quantitative magnetization transfer rate constant image maps were collected from the kidney in vivo. These rate constant images may prove useful in quantitative tissue characterization and in the determination of tissue‐specific 1H relaxation mechanisms. © 1991 Academic Press, Inc.