bluuebunny/crossref_metadata_2025_split huggingface dataset:
31P Spectroscopic localization using pinwheel NMR excitation pulses
Authors: Hardy Christopher J. , Bottomley Paul A. 
Published: March 2007

AbstractSpectroscopic imaging with a one‐dimensional phase‐encoding gradient and surface‐coil reception relies on the restricted range of sensitivity of the surface coil to provide localization in the dimensions transverse to the coil axis and consequently suffers from relatively poor localization in these dimensions. A two‐dimensional (2D) cylindrically selective excitation pulse with a large spectral bandwidth is presented here to remedy this problem. The gradient waveforms are derived from multiple spirals in k space which form an overall pinwheel pattern, resulting in a pulse which is much shorter than the equivalent single‐spiral trajectory. Nonuniform traversal of the spirals further reduces the pulse width under conditions of gradient slew‐rate limitations, yielding overall gains in bandwidth of up to about 30 compared with the equivalent single‐spiral trajectory traversed at constant angular rate. The accompanying rf waveform is obtained by weighted 2D Fourier transformation of the desired sensitivity profile. A new weighting factor is introduced into the rf waveform to compensate for nonuniform sampling of k space by the pinwheel near the origin. This factor is independent of the weighting used to account for the rate of traversal of the trajectory and is applicable to 2D pulse design in general. Pulse sequences employing pinwheel excitation in conjunction with either phase‐encoding or slice‐selective inversion are used to produce multiple‐voxel and single‐voxel localization in a human heart and a phantom. Pinwheel pulses may be used to advantage on moieties with long spin‐lattice relaxation times and short transverse relaxation times and are therefore ideal for applications in phosphorus (13P) NMR. © 1991 Academic Press, Inc.
Motion‐insensitive volume‐selective pulse sequences for direct and proton‐detected 13C spectroscopy: Detection of glycogen in the human liver in vivo
Authors: Knüttel A. , Kimmich R. , Spohn K.‐H. 
Published: March 2007

AbstractTwo compact pulse sequences are reported for the volume‐selective detection of 13C nuclei. 13C signals are either directly acquired after enhancing the amplitude by polarization transfer from the coupled protons or, preferably, indirectly detected by heteronuclear editing of proton signals of 1H nuclei coupled to 13C. In the latter case, the full sensitivity of proton resonance is achieved, and signals from uncoupled protons or protons coupled to non‐13C nuclei or 13C nuclei of undesired compounds are suppressed. Both sequences are single‐scan procedures and are insensitive to the pulse phases and to motions of the investigated organs. The insensitivity to organ motions is due to the extremely compact character of these sequences avoiding coherence evolution periods as far as possible. This is achieved first by the introduction of double‐resonance sandwich (DORSA) pulses accomplishing the polarization transfer slice selectively in a very short time. The second reason is that the initial evolution interval which is usually part of polarization transfer experiments is avoided by the aid of a doublet line‐selective inversion pulse. Several test experiments in vivo are reported. In particular, it is demonstrated that glycogen can be detected in natural abundance in the human liver in vivo using a 2‐T whole‐body tomograph even without the use of heart or respiration triggers. The total acquisition time was 22 min, and a signal‐to‐noise ratio of 6 was achieved. © 1991 Academic Press, Inc.
Double‐quantum surface‐coil NMR studies of sodium and potassium in the rat brain
Authors: Lyon Robbe C. , Pekar James , Moonen Chrit T. W. , McLaughlin Alan C. 
Published: March 2007

AbstractDouble‐quantum filtered and conventional single‐pulse sodium and potassium NMR spectra were obtained from in situ rat brain at 7.0 T, using a surface coil. In contrast to the ca. 14% decrease observed in single‐pulse sodium NMR spectra upon death, increases as large as ca. 800% were observed in double‐quantum filtered sodium spectra. Conversely, a ca. 26% increase was observed in single‐pulse potassium spectra upon death, while double‐quantum filtered potassium spectra decreased below the noise level, for the shortest preparation time used. The decay rate of double‐quantum sodium coherence in the in situ rat brain after death was dependent upon the double‐quantum preparation time: this behavior results from the nonuniformity of the brain, and may be related to physiological com‐partmentalization. The potential application to sodium NMR imaging of cerebral functionality is briefly discussed. © 1991 Academic Press. Inc.
Lipid bilayer and water proton magnetization transfer: Effect of cholesterol
Authors: Fralix Teresa A. , Ceckler Toni L. , Wolff Steven D. , Simon Sidney A. , Balaban Robert S. 
Published: March 2007

AbstractMagnetization transfer between macromolecules and water can be a significant factor contributing to tissue water 1H relaxation. Using saturation transfer techniques, the degree of magnetization transfer between the macromolecular matrix and bulk water 1H can be directly measured and magnetization transfer contrast (MTC) can be generated in MR images. A significant degree of MTC has been observed in tissues with high plasma membrane content such as kidney and brain. The purpose of this study was to establish whether lipid bilayers, as models for cell membranes, could exchange magnetization with the water solvent and whether this effect could contribute to MTC observed in intact tissues. Magnetization transfer was measured in aqueous dispersions of egg phosphatidylcholine (EPC) in the presence and absence of cholesterol. It was found that neither EPC bilayers nor cholesterol by themselves significantly exchanged magnetization with bulk water 1H. However, as the concentration of cholesterol was increased, the pseudo‐first‐order magnetization exchange rate increased to a maximum value of ∼1 s−1. The cholesterol‐induced 1H magnetization exchange may be related either to longer correlation times of the lipid or to an increase in the number of water molecules associated with the bilayer. These results indicate that EPC‐cholesterol bilayers exchange 1H magnetization with bulk water. These results are consistent with lipid bilayer contributions to bulk water relaxation and MTC in intact biological tissues. © 1991 Academic Press. Inc.
A simple method for the restoration of signal polarity in multi‐image inversion recovery sequences for measuring T1
Authors: Gowland P. A. , Leach M. O. 
Published: March 2007

AbstractA simple scheme for the polarity correction of absolute images from inversion recovery multi‐image T1 measurement sequences is described and demonstrated. This method is less sensitive to errors from eddy currents than the conventional full phase correction schemes and does not involve an increase in measurement time as it requires no additional scans. © 1991 Academic Press. Inc.
Three‐point dixon technique for true water/fat decomposition with B0 inhomogeneity correction
Authors: Glover G. H. , Schneider E. 
Published: March 2007

AbstractAn enhancement to Dixon's technique is described which can provide error‐free decomposition of water and fat proton images even in the presence of off‐resonance conditions which result from susceptibility differences, demagnetization, or shim errors. The method uses three measurements with phase shifts of 0, π and − π between the fat and water resonances. The additional information provided by the third measurement is used to calculate an image of the field inhomogeneity in addition to true water and fat images. The signal‐to‐noise ratio (SNR) in the decomposed images is equivalent to that of a 2.7 NEX acquisition (instead of 3 NEX), yielding an SNR imaging efficiency of 95%. In addition, the B0 image which is provided may have diagnostic value in its own right. Examples of head and body scans often portray surprisingly large B0 shifts near interfaces between air or bone and soft tissue. © 1991 Academic Press. Inc.
Restricted and anisotropic displacement of water in healthy cat brain and in stroke studied by NMR diffusion imaging
Authors: Moonen Chrit T. W. , Pekar James , de Vleeschouwer Marloes H. M. , van Gelderen Peter , van Zijl Peter C. M. , Despres Daryl 
Published: March 2007

AbstractThe occlusion of the middle cerebral artery in cat brain was used as an experimental stroke model to investigate the physical basis of the recently reported lowered diffusion constant of water in acute infarcted brain tissue (Moseley et al., Magn. Reson. Med. 14, 330, 1990). The original findings were confirmed in this study of 12 animals investigated with the diffusion‐sensitized stimulated echo sequence. The following additional results were obtained: First, the onset of significant lowering of the diffusion constant in the stroke area varied significantly (up to 2.5 h depending on the animal). Second, the affected area is much more clearly outlined in diffusion‐weighted images than in T2,‐weighted images, even in the period between 3 to 12 h following occlusion. Third, for diffusion times between 50 and 2000 ms, the diffusion constant of water is independent of diffusion time in healthy tissue, as well as in the stroke area. Fourth, the diffusion anisotropy is similar in healthy and in stroke area and remains similar regardless of the diffusion time used. © 1991 Academic Press, Inc.
Multinuclear MR investigation of the metabolic response of the murine RIF‐1 tumor to 5‐fluorouracil chemotherapy
Authors: Sijens Paul E. , Baldwin Nicholas J. , Ng Thian C. 
Published: March 2007

AbstractThe metabolic response of the RIF‐1 tumor to 5‐fluorouracil (a single dose of 260 mg 5FU/kg, ip) was monitored in 10 mice using 19F and 31P MR spectroscopy. 19F MRS revealed a continuous drop in tumor 5FU level and an increase in the fluoronucleotide (Fnuc) signal to a plateau value of 50% of the initial 5FU level, during the first 2 h after chemotherapy. Although the 31P MR spectra of the tumors showed no significant initial changes, the total level of MR visible tumor phosphate decreased and tumor pH increased during the subsequent days. The changes in phosphate metabolism and tumor pH did not correlate with the detected fluorine levels or tumor response. However, the pretreatment Pi level, the plateau Fnuc level, and the 5FU induced decrease in tumor volume showed significant correlation. The indicates that both 19F and 31P MR spectroscopy have potential for predicting reponse to 5FU chemotherapy. © 1991 Academic Press, Inc.
Sequential 2D inflow venography: Initial clinical observations
Authors: Lanzer P. , Gross G. M. , Keller F. S. , Pohost G. M. 
Published: March 2007

AbstractSequential 2D inflow NMR (SDI) venography was employed to define venous anatomy and pathology in five healthy subjects and five patients, mean age 48 ± 7 years, with documented deep vein thrombosis. SDI images were graded independently by two observers on a scale of 1,2 nondiagnostic and 3,4 diagnostic categories. All iliac and femoropopliteal SDI venograms were diagnostic. In contrast, only one out of nine calf SDI venograms was diagnostic. SDI is a promising new method to assess the proximal peripheral venous system. Improved imaging strategy is needed to produce flow images of the calf veins. © 1991 Academic Press, Inc.
Quantitation of metabolites by 1H NMR
Authors: Pan J. W. , Hetherington H. P. , Hamm J. R. , Shulman R. G. 
Published: March 2007

AbstractIn this report we describe the three factors that need to be measured when quantitating an edited resonance relative to an internal standard using a surface coil. These factors are necessary by virtue of the water, fat suppressing, and localization schemes used in studying a 1H metabolite. First, use of semi‐selective pulses requires amplitude correction of the edited and reference resonances. Second, use of a single surface coil results in different sensitive volumes for different resonances due to the inhomogeneous B1 and therefore requires separate acquisition of the resonances. Third, editing pulses alter the sensitive volumes and this correction must be made internally by applying the same editing pulse to the reference resonance. A rationalization of this correction is given in terms of rotation operators. We apply these corrections to quantitate edited lactate relative to total creatine in a MnCl2‐doped phantom and find 91% rather than 145% of known concentration. In human skeletal muscle in vivo after exhaustive exercise, we measured the lactate after exercise and found it to be 27.2 mM in two experiments, in reasonable agreement with literature values for the given exercise protocol. © 1991 Academic Press, Inc.
Factors in myocardial “Perfusion” imaging with ultrafast MRI and Gd‐DTPA administration
Authors: Burstein Deborah , Taratuta Eleina , Manning Warren J. 
Published: March 2007

AbstractUltrafast magnetic resonance imaging (MRI) and first pass observation of an interstitial contrast agent are currently being used to study myocardial perfusion. Image intensity, however, is a function of several Parameters, inculding the delivery of the contrast agent to the intersitium (coronary flow rate and diffusion into the intersitium) and the relaxation properties of the tissue (contrast agent concentration, proton exchange rates, and relative intra‐and extracellular volume fractions). In this study, image intensity during gadopen tetate dimeglumine (Gd‐DTPA) adminstration with T1 weighted ultrafast MR imaging was assessed in an isolated heart preparation. With increasing Gd‐DTPA concentration the steady‐state myocardial image intensity increased but the time to reach steady state remained unchanged, resulting in an increased slope of image intensity change. A range of physiologic perfusion pressures (and resulting coronary flow rates) had insignificant effects on Gd‐DTPA in wash in or steady‐state image intensity, suggesting that diffusion of Gd‐DTPA into the interstitium is the rate limiting step in image intensity change with this preparation. Following global ischemia and reperfusion, transmural differences in the slope of image intensity change were apparent. However, the altered steady state image intensity (due to postichemic edema) makes interpretation of this finding difficult. The studies described here demonstrte that although Gd‐DTPA administration combined with ultrafast imaging may be a sensitive indicator of perfusion abnormalities factors other than perfusion will affect image intensity. Extensive studies will be required before image intensity with this protocol is fully understood. © 1991 Academic Press, Inc.
Spoiling of transverse magnetization in steady‐state sequences
Authors: Zur Y. , Wood M. L. , Neuringer L. J. 
Published: March 2007

AbstractA detailed analysis is presented of a method to eliminate transverse magnetization prior to each rf excitation in pulse sequences with TR < T2. It is shown that artifact‐free images with high T1 contrast can be obtained only if a phase shift that is incremented during each TR interval is applied to the transverse magnetization. Computer simulations are used to show that when this phase increment is 117°, the steady‐state transverse magnetization prior to each rf pulse is nulled over a wide range of T1, T2, and rf tip angles, resulting in optimal T1, contrast. Such nulling of steady‐state transverse magnetization cannot be obtained by using large gradient pulses, or gradients of random or linearly incremented amplitude. Images of phantoms and human subjects confirm the theoretical predictions. © 1991 Academic Press, Inc.
From the relaxivity of Gd(DTPA)2− to everything else
Authors: Koenig Seymour H. 
Published: March 2007

AbstractWe resolve the observed magnetic field‐dependent relaxivity of Gd (DTPA)2− into inner and outer sphere contributions by comparison with theory. After noting that the outer sphere part, which contributes comparable to both 1/T1 and 1/T2, is identical to the “susceptibility” effect, we demonstrate the transition from the outer sphere relaxivity of small complexes, e. g. Gd(DTPA)2−, to that of large magnetic particulates, e. g., magnetite, used as T2 agents. This transition is expressed as a shift from a quantum to a classical mechanical description of relaxivity. We next show how to extrapolate the inner sphere contribution of Gd(DTPA)2− to similar small agents with greater structural symmetry, e. g., Gd(NOTA)−, by lengthening the electronic relaxation time and to ternary macromolecular complexes of small agents with protein by lengthening the rotational relaxation time. Finally, we indicate how relatively large lipid vesicles containing either small paramagnetic complexes or magnetized particulates may be considered analogs of Gd(DTPA)2−, with analogous inner and outer sphere contributions. © 1991 Academic Press, Inc.
Gd‐BOPTA/Dimeg: Experimental disease imaging
Authors: Cavagna Friedrich , Daprà Massimo , Maggioni Fabio , De Haën Christoph , Felder Ernst 
Published: March 2007

AbstractThe novel tissue‐specific contrast agent, Gd‐BOPTA/Dirmeg, was tested in MR imaging of experimental focal liver disease and of acute myocardial ischemia in rats. Directly implanted liver tumors and blood‐borne metastases were used as models for focal liver disease and occlusion of the lower anterior descending coronary artery as model for acute ischemia. The studies with implanted tumors, at a dose level of 250 μmol/kg, showed a very high (370%) and persistent (>2h) increase in the tumor‐liver contrast‐to‐noise ratio (CNR), owing to selective enhancement of normal liver parenchyma signal intensity. While all blood‐borne metastases showed a similar late CNR enhancement, some of them experienced early contrast loss due to transient signal intensity enhancement. In myocardial imaging. Gd‐BOPTA/Dimeg produced a signal intensity enhancement in normal myocardium and an injured area‐normal area CNR enhancement which were both much stronger and more presistent than those produced by Gd‐DTPA/Dimeg. © 1991 Academic Press, Inc.
Porphyrins as contrast media
Authors: Nelson James A. , Schmiedl Udo 
Published: March 2007

AbstractThe interest in tissue distribution of variously labeled or otherwise detectable natural and synthetic porphyrins and porphyrin derivatives dates back well over 60 years. Although a considerable interest in fluorescent turnor localization and therapy dominates the history of porphyrin biodistribution studies, many investigators have evaluated the diagnostic and therapeutic characteristics of porphyrins with radioactive, radiopaque, and paramagnetic qualities. In this paper, a review of the use of porphyrins as nuclear medicine, X‐ray, and NMR contrast agents is presented. © 1991 Academic Press, Inc.
Contrast agents for magnetic resonance spectroscopy: A method to obtain increased information in in vivo and in vitro spectroscopy
Authors: Swartz Harold M. , Chen Kai , Hu Huping , Hideg Kalman 
Published: March 2007

AbstractThe concept of contrast, which now is an integral part of many magnetic resonance imaging studies, can be extended successfully to magnetic resonance spectroscopy. It involves the use of paramagnetic molecules whose distribution is restricted in some manner, thereby causing differential effects on the NMR spectra. As an illustrative example, the effects of tipophilic nitroxide stable free radicals on the NMR spectra of serum and lipoproteins are shown. These nitroxides differentially broaden away components of the spectra due to the nuclei of methylene and methyl groups, which enables the usually obscured peaks of lactate to be observed fully. The concept can be applied to differential distribution of the contrast agent on the basis of solubility, charge, and/or compartmentalization. It can be used with any type of NMR spectroscopy and any type of paramagnetic contrast (broadening) agent. © 1991 Academic Press, Inc.
Quantitative Two‐Dimensional time Correlation Relaxometry
Authors: English A. E. , Whittall K. P. , Joy M. L. G. , Henkelman R. M. 
Published: March 2007

AbstractAn experimental and analytical method is presented for obtaining two‐dimensional NMR time correlation spectra of T1 and (T2 and T2) exponential relaxation in heterogeneous samples. The numerical algorithms used in this study do not bias the solution by any a priori assumptions as to the number of required components. The constraints used to overcome the ill‐posed and ill‐conditioned nature of this inverse problem are also described. With this method, the correlations of T1 (or T1) and T2 exponential components in systems of nonexchanging standards and rat muscle tissues are obtained. © 1991 Academic Press, Inc.
Quantification of myocardial blood flow and extracellular volumes using a bolus injection of Gd‐DTPA: Kinetic modeling in canine ischemic disease
Authors: Diesbourg Leo D. , Prato Frank S. , Wisenberg Gerald , Drost Dick J. , Marshall Tara P. , Carroll S. Edwin , O'Neill Blair 
Published: March 2007

AbstractIn order to clarify the relationship between coronary artery disease (including myocardial infarction) and image contrast in gadolinium diethylenetriaminepentaacetic acid (Gd‐DTPA‐enhanced MRI it was decided to model the myocardial tissue distribution and clearance of Gd‐DTPA using the modified Kety equation. Using a canine model, myocardial tissue Gd‐DTPA concentrations ([Gd‐DTPA]m) were measured 1 or 5 min after a bolus injection of Gd‐DTPA or immediately after the end of a constant infusion of Gd‐DTPA in a total of 35 dogs. It was found that within 5 min of a bolus injection [Gd‐DTPA]m is determined primarily by myocardial blood flow (MBF) and after about 10 min primarily by myocardial extracellular volumes (MECV). This study suggests that repeat, rapid (every 2–4 s) measurements of myocardial T1 relaxation rates following the bolus injection of Gd‐DTPA are required to calculate MBF (i.e., myocardial tissue perfusion) and MECV. © 1992 Academic Press, Inc.
Quantitative MRI studies for assessment of multiple sclerosis
Authors: Pannizzo F. , Stallmeyer M. J. B. , Friedman J. , Jennis R. J. , Zabriskie J. , Plank C. , Zimmerman R. , Whalen J. P. , Cahill P. T. 
Published: March 2007

AbstractAlthough magnetic resonance imaging (MRI) is a valuable aid in the initial diagnosis of multiple sclerosis (MS), quantitatively MRI has been disappointing in staging and evaluating therapy protocols by means of serial examinations. In this study, image processing algorithms were developed for the global analysis of MR images of the cerebrum. Limited three‐dimensional segmentation was achieved through histogram analysis by these algorithms, which are essentially operator independent. The effects of coil response and tip angles, patient positioning, and interslice gap thicknesses were examined for 10 MS patients with repeated examinations for a total of 72 images. Effects of technique and instrumentation errors were approximately 6%, and agreement between two independent operators for measuring the total MR pixel sum from periventricular effusions and intense MS plaques was better than 97% with a standard deviation of 2.9%. © 1992 Academic Press, Inc.
Error in the calibration of the mgatp chemical‐shift limit: Effects on the determination of free magnesium by 31P NMR spectroscopy
Authors: Mosher Timothy J. , Williams Gerald D. , Doumen Chris , Lanoue Kathryn F. , Smith Michael B. 
Published: March 2007

AbstractThe measurement of free intracellular magnesium (Mg2+) using the 31P chemical shifts of ATP requires the use of appropriate calibration solutions to determine the chemical‐shift limits ΔATPαβ and ΔMgATPαβ. Solutions containing excess Mg2+ contain significant amounts of Mg2ATP and yield positive errors in the value of ΔMgATPαβ. For physiological applications this may overestimate free intracellular Mg2+ by as much as 300%. This error may be minimized if appropriate mole ratios of Mg2+/ATP are used to calibrate ΔMgATPαβ. © 1992 Academic Press, Inc.