bluuebunny/crossref_metadata_2025_split huggingface dataset:
Simultaneous cardiac mechanics and phosphorus‐31 NMR spectroscopy during myocardial ischemia and reperfusion in the intact dog
Authors: Miller D. Douglas , Salinas Felix , Walsh Richard A. 
Published: March 2007

AbstractTo investigate the high‐energy phosphate metabolic correlates of left ventricular (LV) dysfunction during the onset and recovery from severe, global myocardial ischemia in vivo, seven preinstrumented closed‐chest dogs had ECG‐gated phosphorus‐31 (31P) NMR‐spectroscopy (NMR‐S) studies performed and LV micromanometer and sonomicrometer data measured before, during, and every 5 min following severe occlusive global myocardial ischemia. Ischemic LV + dP/dtmax fell from 2396 ± 576 mm Hg/s at baseline to 2185 ± 478 mm Hg/s (p < 0.05) and did not normalize until after 30 min of reperfusion. LV ejection fraction (EF) decreased significantly (0.32 ± 0.07 EF units to 0.12 ± 0.13 EF units; P < 0.05) and did not recover by 30 min of reperfusion (0.27 ±0.09 units; P < 0.05 vs baseline). Simultaneous 31P NMR‐S studies demonstrated excellent β ‐ATP signal‐to‐noise (10 ± 4:1). Myocardial acidosis occurred during global ischemia (ApH = −0.22 ± 0.23 units; p < 0.05), with recovery at 30 min of reperfusion. Inorganic phosphate/ phosphocreatine ratio (Pi/PCr) increased significantly during ischemia (0.46 ± 0.07 to 0.61 ± 0.07; P < 0.05), with delayed normalization of this ratio at 30 min of reperfusion. β‐ATP peak area did not change during ischemia. Pi/PCr and LV contractility ( + dP/ dtmax ) were significantly correlated at baseline (r = −0.70) and during global ischemia (r = −0.78; p < 0.01), but not during recovery (r = 0.006; p = NS). Therefore, the simultaneous evaluation of high‐fidelity hemodynamic data and topical 31P NMR‐S can be performed in the intact State. © 1991 Academic Press, Inc.
The use of gradient flow compensation to separate diffusion and microcirculatory flow in MRI
Authors: Maki Jeffrey H. , Macfall James R. , Johnson G. Allan 
Published: March 2007

AbstractThis paper describes a new MR imaging technique termed Modified Stejskal Tanner versus Flow Compensation (MST/FC) for the separation of diffusion and microcirculatory flow. The theory behind the sequence is explained, along with a five‐component model of microcirculation applicable to any “perfusion” imaging technique. Phantom data is presented showing that (1) diffusion effects can be matched between MST and FC (suggesting the possibility of flow‐compensated diffusion imaging), and (2) the technique is a quantitative method of separating diffusion and slow (<0.25 mm/s) tortuous flow through a Sephadex column. Furthermore, animal images show the technique to be feasible and quantitative in measuring rat brain microcirculation under normal, vasodilated (hypercarbia), and no‐flow (post mortem) conditions. © 1991 Academic Press, Inc.
Phosphonate‐modified GdDTPA complexes. I. NMRD study of the solution behavior of new tissue‐specific contrast agents
Authors: Adzamli I. Kofi , Blau Monte 
Published: March 2007

AbstractNMRD profiles, the magnetic field dependence of the water proton longitudinal relaxation rates, have been acquired for two new diphosphonate‐modified GdDTPA complexes currently under evaluation as relaxation agents for the MRI detection of soft‐tissue calcifications. Fresh dilute solutions show profiles identical to that of unmodified GdDTPA, which remain unchanged for up to 9 weeks. Solutions containing Gd species at MRI significant concentrations, 100 to 500 mM, show the presence of oligomers (n = 5 or more) upon aging, with much higher high‐field relaxivities. Aggregation is attributed to the interactions between a gadolinium center and the phosphonate terminus of a neighboring molecule, and is prevented by esterification of the phosphonate terminus. Oligomers are also easily disrupted by dilution with phosphate‐buffered saline, where the exogenous phosphate ions compete with the phosphonate. Other nucleophiles such as are present in protein side chains of bovine serum albumin also compete with the phosphonate in these associations, the result being species with even higher relaxivities. © 1991 Academic Press, Inc.
Effect of homonuclear J modulation on 19F spin‐echo images
Authors: Babcock Evelyn E. , Mason Ralph P. , Antich Peter P. 
Published: March 2007

AbstractThe effect of homonuclear J modulation on 19F spin‐echo images is evidenced by a substantial reduction in signal when the echo time, TE, approaches 1 /2J, with a subsequent increase in signal at longer TEs. Suppression of the J‐modulation effect is demonstrated using chemical Shift‐Selective 180° refocusing pulses. © 1991 Academic Press, Inc.
Effect of aging and diet on proton NMR spectra of rat urine
Authors: Bell J. D. , Sadler P. J. , Morris V. C. , Levander O. A. 
Published: March 2007

Abstract500 MHz 1H NMR studies of rat urine are used to assess metabolic changes resulting from aging (0.5‐20 months) and changes in diet (casein versus chow). Aging rats fed chow diets decrease their excretion of citrate and 2‐oxoglutarate, while the output of taurine and creatinine increases. Only young rats (1 month or less postweaning) excrete significant amounts of betaine and trimethylamine‐N‐oxide. Rats fed casein diets for 1 month postweaning do not excrete 2‐oxoglutarate and excrete lower levels of hippurate, succinate, and citrate compared to rats fed chow diets. They also excrete N‐methylnicotinamide. These high resolution proton NMR studies provide metabolic profiles which are not readily available by other techniques. © 1991 Academic Press, Inc.
An evaluation of new processing protocols for in vivo NMR spectroscopy
Authors: Mazzeo A. R. , Levy G. C. 
Published: March 2007

AbstractIn vivo NMR spectroscopy is often complicated with problems of low signal‐to‐noise, poor resolution, undefined peak shapes, and nonlinear baselines despite the efforts of investigators to optimize their experiments. Several data processing options are available to spectroscopists to enhance resolution and signal‐to‐noise and /or to flatten baselines. There is some question about how these processing protocols affect quantitative information. This paper evaluates five different processing protocols for their ability to extract quantitative information from a set of nonideal spectra. Three of the protocols involve recently developed statistical signal processing methods, maximum entropy Fourier spectral deconvolution, linear prediction singular value decomposition, and baseline deconvolution. These protocols are compared with the conventional processing methods of convolution difference and zeroing initial data points of the FID. The methods are evaluated by use of a quantitative 31P model sample and also are demonstrated on surface coil 31P data. © 1991 Academic Press, Inc.
Use of Paramagnetic Chelated Metal Derivatives of Polysaccharides and Spin‐Labeled Polysaccharides as Contrast Agents in Magnetic Resonance Imaging
Authors: Bligh S. W. A. , Harding C. T. , Sadler P. J. , Bulman R. A. , Bydder G. M. , Pennock J. M. , Kelly J. D. , Clatham I. A. , Marriott J. A. 
Published: March 2007

AbstractSoluble and insoluble polysaccharides were derivatized with diethylenetriaminepentaacetic acid (DTPA) and/or spin‐labeled with 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO). Polysaccharides derivatized with DTPA were prepared via cyanogen bromide activation, coupling to a diamine linker, and to DTPA anhydride. Spin‐labeled polysaccharides were also prepared via cyanogen bromide activation. The extent of derivatization for dextran (18 kDa) was about 120 glucose units per DTPA, and for cellulose and starch about 15–30 units per DTPA. For spin‐labeled polysaccharides, the average loading ranged from 1 nitroxide per 16 glucose units for starch to 181 for dextran (82 kDa). These derivatized paramagnetic polysaccharides were shown to be more effective relaxants than the small paramagnetic molecules alone. Both soluble and insoluble polysaccharide‐linker‐DTPA‐Gd(III) complexes were effectively cleared from the body (rats) after oral administration. After intravenous administration, the biodistribution of dextran‐linker‐DTPA‐Gd(III) complexes differed significantly from that of GdDTPA. Reduction of the nitroxide by ascorbic acid was retarded in the polysaccharide derivatives, particularly in starch enrivatized with both nitroxide and linker‐DTPA‐Cu(II). These agents showed contrast enhancement in the gastrointestinal tract of rabbits. © 1991 Academic Press, Inc.
A pitfall associated with lactate detection using stimulated‐echo proton spectroscopy
Authors: Sotak Christopher H. , Alger Jeffry R. 
Published: March 2007

AbstractAt TE values of 136 ms, it has recently been shown that the lactate methyl signal, when obtained with a stimulated‐echo (STE) sequence, is modulated at the zero‐quantum (ZQ) frequency when TM is varied. Here we describe an additional modulation of the ZQ lactate signal, due to spin‐spin coupling, that results in a 10‐fold reduction in the lactate signal for TM intervals ranging between 48 and 84 ms (and at multiples of 136 ms thereof). Because of this J‐modulation, improper choice of TE and TM intervals may give false negative results for lactate detection by STE spectroscopy. © 1991 Academic Press, Inc.
Ultrafast Low‐Angle RARE: U‐FLARE
Authors: Norris David G. 
Published: March 2007

AbstractThe subsecond application of the RARE technique is described. Two possible methods of implementation are discussed, one in which T2 contrast is manipulated by temporal reordering of the phase‐encoding gradient, and the other in which the phase‐encoding order is held constant and the contrast is manipulated by means of a spin‐echo preparation experiment. In vivo images obtained with the latter method are presented and applications of the sequence discussed. © 1991 Academic Press, Inc.
Rebound alkalosis and persistent lactate: Multinuclear (1H, 13C, 31P) NMR spectroscopic studies in rats
Authors: Nakada Tsutomu , Houkin Kiyohiro , Hida Kazutoshi , Kwee Ingrid L. 
Published: March 2007

AbstractIntracellular pH levels of infarcted brain determined by phosphorus‐31 nuclear magnetic resonance (NMR) spectroscopy disclosed a notable phenomenon. The acidotic brain pH seen in the acute stage of infarction was observed to rebound into the alkalotic range in the subacute phase before returning to the normal range in the chronic phase. This “rebound alkalosis” which was usually observed between the 24th and the 48th hour after experimental induction of infarction in rats was accompanied by significant lactate levels as detected by proton NMR spectroscopy. Analysis of the satellite methyl resonance of 13C‐lactate using high‐resolution proton NMR spectroscopy after 13C‐glucose infusion indicated that no lactate was produced in the subacute phase of infarction and that the lactate detected during this phase must have been generated prior to this phase of infarction. © 1991 Academic Press. Inc.
A new acquisition mode for 2D inflow refreshment angiography
Authors: Doyle Mark , Matsuda Tetsuya , Pohost Gerald M. 
Published: March 2007

AbstractTime‐of‐flight angiography methods rely on blood/tissue contrast generated when fresh blood spins enter a partially saturated region. A series of projective angiographic views is generated by application of a maximum intensity projection algorithm to data acquired from a 3D volume. When the data are acquired as a set of 2D slices, the angiograms exhibit sensitivity to body motion, resulting in the generation of artifacts. We present a new 2D time‐of‐flight angiographic technique, STREAM, Suppressed Tissue with Refreshment Angiography Method. It exhibits low sensitivity to internal body motion, thus allowing acquisition of good quality, single average angiograms. To suppress the static tissue signal a unique “active” suppression strategy is employed. Additionally, to further suppress the lipid signal, the chemical‐shift phenomenon is exploited in the STREAM sequence. © 1991 Academic Press. Inc.
New spatial localization method using pulsed high‐order field gradients (SHOT: Selection with high‐order gradient)
Authors: Oh C. H. , Hilal S. K. , Cho Z. H. , Mun I. K. 
Published: March 2007

AbstractA new spatial localization method using an additional set of high‐order magnetic field gradients is described. The method uses a nonlinear part of high‐order magnetic field gradient patterns which allows us to select a volume in conjunction with the selective radiofrequency (RF) pulse. Unlike the other existing volume selection methods such as ISIS or SPARS, the proposed selection method requires only one RF‐gradient pulse pair to select a volume in two directions. The center of the selected volume can be moved to any arbitrary location within the body by the addition of precalculated lower order gradients which are simultaneously pulsed with the high‐order gradient. The method also has the potential for localized spectroscopy from the FID signal which can be realized by using oscillating second‐ and first‐order gradients for 3D selection with a single RF pulse. By using the proposed localization method, it is possible to design more flexible pulse sequences, e.g., the shorter echo‐time spectroscopic pulse sequence. We have designed and constructed a six‐loop r2 (or x2 + y2) gradient coil for initial application. By simultaneously applying this second‐order gradient and proper x, y, and/or z gradients, 2D selections were achieved in arbitrarily selected positions in conjunction with a single selective RF pulse. Phantom and animal experiments have been performed and the results appear promising, especially in areas of NMR spectroscopic imaging applications where spatial localization is essential. © 1991 Academic Press. Inc.
Target‐point combination of MR images
Authors: Buxton Richard B. , Greensite Fred 
Published: March 2007

AbstractA method is described for combining multiple magnetic resonance images of the same anatomic slice to produce a single image which incorporates the favorable contrast features of each of the original images. The target‐point method is a general method that includes linear combination as a subset and is designed to deal with the clinical need to maximize the contrast‐to‐noise ratio between several pairs of tissues simultaneously. Although it is intrinsically a nonlinear method, noise propagates approximately uniformly into the combined image. In examples of brain images the target‐point method produced images with higher mutual contrast than the first principal component weighted sum image. © 1991 Academic Press. Inc.
A modified pulse sequence for in vivo diffusion imaging with reduced motion artifacts
Authors: Prasad P. V. , Nalcioglu O. 
Published: March 2007

AbstractA modified spin‐echo diffusion imaging pulse sequence incorporating bipolar gradients that is less sensitive to macroscopic motion‐induced artifacts is presented. Expressions for apparent diffusion coefficient in the presence of microcirculation and macroscopic motions and contrast‐to‐noise ratio in the diffusion map are derived. Diffusion coefficients of liquid phantoms have been measured using a 1.5‐T GE Signa system. Experiments performed to demonstrate the immunity to motion‐induced errors are reported. Brain images from human volunteer have also been included to show the potential clinical application of the proposed pulse sequence. © 1991 Academic Press. Inc.
Adaptive motion compensation in MRI: Accuracy of motion measurement
Authors: Felmlee Joel P. , Ehman Richard L. , Riederer Stephen J. , Korin Hope W. 
Published: March 2007

AbstractIt has been shown that magnetic resonance image data can be corrected for the effects of motion by using retrospective adaptive techniques which employ navigator (NAV) echoes. We demonstrate the accuracy with which NAV echoes can measure motion, as well as the independent nature of the respective view‐to‐view and intraview corrections. © 1991 Academic Press. Inc.
The effect of chlorpromazine and methylprednisolone on NMR relaxation times in the normal cat brain
Authors: Barnes D. , Harvey I. , McDonald W. I. , Ron M. A. , Moore S. 
Published: March 2007

AbstractThis small experimental study describes the effects on the NMR relaxation times in normal cat brain of a 5‐day course of high dose methylprednisolone and, separately, a 1‐month course of standard dose daily chlorpromazine. Methylprednisolone had no influence on T1 or T2 in these tissues, but chlorpromazine produced a transient fall of T1 of thalamus, and rise in T2 of white matter: both normalize after 4 weeks. The mechanism of these changes is unknown. It is concluded that these drugs should not interfere with the quantitative MRI monitoring of brain abnormalities in patients receiving them, although the unlikely occurrence of longer term effects of chlorpromazine has not been excluded. © 1991 Academic Press. Inc.
Evidence for a contribution of paramagnetic ions to water proton spin‐lattice relaxation in normal and malignant mouse tissues
Authors: Negendank William , Corbett Thomas , Crowley Michael , Kellogg Christopher 
Published: March 2007

AbstractParamagnetic ions complexed to proteins may lose, retain, or enhance solvent paramagnetic relaxation (SPR) relative to free solution. We measured T1 and T2 of three mouse cancers, their normal counterparts, and six additional tissues. Long T1 of cancers was not caused by necrosis or by different contents of water, fat, or blood. Dissociable (TCA‐extractable) and nondissociable (ashed) Mn, Cu, and Fe were measured by AA. Cancers had less Mn, Cu, and Fe than did normal counterparts. All 12 tissues had inverse correlations between T1 and dissociable Mn and Cu. For Mn alone to account for reduced T1, the extent to which SPR of the Mn‐protein complexes would be enhanced is by factors of 0.6 to 13, below the maximum observed in Mn‐enzymes. Different amounts of paramagnetic ion‐protein complexes may account for part of the differences in T1 of water protons in different tissues, and the longer T1 of cancer cell water may be caused in part by reduced amounts Of such complexes. © 1991 Academic Press. Inc.
Volume imaging with MR phased arrays
Authors: Hayes Cecil E. , Hattes Neil , Roemer Peter B. 
Published: March 2007

AbstractA volume MR phased array was constructed with two coils placed anteriorly and two coils posteriorly. Data acquired simultaneously from the four coils on a phantom were combined into a single image having a signal‐to‐noise ratio 80% better than that from the body coil. Additional comparisons of the four‐coil phased array with a two‐coil phased array and a Helmholtz pair having the same overall dimensions show how variations of signal amplitude and phase in the individual coils affect the composite SNR. Images of the male and female pelvis demonstrate how the improved SNR can be used to reduce the number of excitations, decrease the field of view, increase the echo time, or reduce the slice thickness. © 1991 Academic Press. Inc.
Rapid in vivo proton shimming
Authors: Schneider Erika , Glover Gary 
Published: March 2007

AbstractA rapid and completely automated method of adjusting the magnetic field (B0) homogeneity for in vivo proton spectroscopy and imaging is described. Bo inhomogeneity maps are generated by a gradient‐recalled echo pulse sequence in which the frequency dispersion is chosen to eliminate the effects of the fat/water chemical shift. Low‐order shim values are derived by magnitude‐weighted least‐squares fits to the B0 maps and automatically applied as DC offsets to the X, Y, and Z gradient amplifiers. Imaging with chemical shift selective saturation is used as a measure of the efficacy of the technique. Results indicate that AUTOSHIM improves the overall homogeneity; however, local high‐order field distortions which cannot be corrected by linear gradients are generated by certain air/tissue and bone/tissue morphology. In such cases a “ZOOM SHIM” may be applied over a limited region of interest for local homogeneity improvement at the expense of other regions. It is suggested that such scans are a necessity for recording the homogeneity during clinical MR spectroscopy. © 1991 Academic Press. Inc.
In vivo NMR spectral parameter estimation: A comparison between time and frequency domain methods
Authors: Joliot M. , Mazoyer B. M. , Huesman R. H. 
Published: March 2007

AbstractWe have compared various methods of in vivo NMR spectral parameter estimation, namely a nonlinear fit of the free induction decay signal in the time domain (NLTD), a nonlinear fit of the fast Fourier transform of the FID data in the frequency domain using either a continuous Lorentzian model (NLLM) or a Fourier‐sampled model (NLFM), and a time‐domain linear prediction method using singular value decomposition (LPSVD). Monte Carlo simulations of 31P and 13C in vivo experiments were used to assess the bias and statistical uncertainties of spectral parameters obtained with each method. In the 31P case, all methods appear to be equivalent except the LPSVD method that led to significantly biased peak amplitudes (up to 28%). In the 13C case, the only methods able to recover the glycogen peak were the NLTD method and its equivalent in the frequency domain (NLFM). In both the 31P and the 13C cases simulations demonstrated that 256 data points were sufficient. These results demonstrate the feasibility and the robustness of a nonlinear fit of the FID data in the time domain, and we illustrate this on 31P and 13C data sets obtained in humans. © 1991 Academic Press. Inc.
A quantitative comparison of the TERA modeling and DFT magnetic resonance image reconstruction techniques
Authors: Smith M. R. , Nichols S. T. , Constable R. T. , Henkelman R. M. 
Published: March 2007

AbstractThe resolution of magnetic resonance images reconstructed using the discrete Fourier transform (DFT) algorithm is limited by the effective window generated by the finite data length. The transient error reconstruction approach (TERA) is an alternative reconstruction method based on autoregressive moving average (ARMA) modeling techniques. Quantitative measurements comparing the truncation artifacts present during DIT and TERA image reconstruction show that the modeling method substantially reduces these artifacts on “full” (256 × 256), “truncated” (256 × 192), and “severely truncated” (256 × 128) data sets without introducing the global amplitude distortion found in other modeling techniques. Two global measures for determining the success of modeling are suggested. Problem areas for one‐dimensional modeling are examined and reasons for considering two‐dimensional modeling discussed. Analysis of both medical and phantom data reconstructions are presented. © 1991 Academic Press, Inc.
A coupled resonator model of the detection of nuclear magnetic resonance: Radiation damping, frequency pushing, spin noise, and the signal‐to‐noise ratio
Authors: Guéron M. 
Published: March 2007

AbstractMagnetic resonance involves two coupled resonating systems: the spins and the tuned receiver coil. We simulate the spin system by an equivalent electrical resonator. An analysis of coupled resonators leads to a straightforward derivation of properties such as radiation damping, frequency pushing, and spin noise. The theory is applied to recent experiments (M. Guéron and J. L. Leroy, J. Magn. Reson. 85, 209–215 (1989)). The sensitivity of the spin noise experiment is shown to be T2/τ0, where 1/τ0 is the rate of radiation damping. This result leads directly to a fundamental formulation of the usual signal‐to‐noise ratio,

where m0 is the equilibrium magnetic moment, θ is the temperature, and F is the noise figure of the receiver. An equivalent electrical resonator can also be used to describe the active medium of masers. © 1991 Academic Press, Inc.