摘要:

AbstractThe kinetics of the CK reaction in the living rabbit brain was studied by three31P magnetization transfer methods: inversion recovery (IR), inversion transfer (IT), and steadystate saturation transfer (SSST). Longitudinal relaxation rates (T−1) were determined from IR and IT experiments. The values were 0.88 ± 0.08 s−1for PCr and 2.45 ± 0.39 s−1for γ‐ATP. Analysis of the results of SSST experiments in which γ‐ATP was saturated yielded a forward rate constantkFof 0.53 ± 0.07 s−1. Upon saturation of PCr no change in the γ‐ATP signal could be detected in SSST. An average reverse rate constant (kR± S.D.) of 0.52 ± 0.04 s−1was estimated by analyzing IT data from three experiments with selective inversion of γ‐ATP. The standard error ofkRwas 50%. The average [PCr]/[ATP]of 1.21 ± 0.16 together with the values ofkFandkRyielded a forward‐to‐reverse flux ratio of 1.23. Within our limits of accuracy this ratio was not significantly different from 1.0, thus suggesting that in the brain the forward and reverse CK fluxes are eq

ISSN:0740-3194    

DOI:10.1002/mrm.1910050102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY

摘要:

AbstractThe contrast‐to‐noise ratio (CNR) in three types of computed MR images is compared in a computer simulation. The original data consist of two spin‐echo or two saturationrecovery images. Each pair of images is used to generate a relaxation time image, a synthetic image at arbitrary echo or repetition time, and an image which is a weighted sum of the original images. The CNR produced by these three methods is compared for signals spanning a wide range of relaxation times. In every comparison an optimally weighted sum produces the highest CNR that is statistically attainable. The CNR in the optimum synthetic image equals this bound only if contrast reversal does not occur in the original images. The CNR in relaxation time images is always less than the statistical bound and can be less than the CNR in the original images. © 1987 Academic Pres

ISSN:0740-3194    

DOI:10.1002/mrm.1910050103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY

摘要:

AbstractProton NMR methods can monitor mobile lipids (e.g., fatty acids and glycerides) in intact tissue. Lipids play a major role in cardiac energy production, and elevated levels of myocardial lipids have been reported following an ischemic insult. The present study examines the potential of high‐resolution1H NMR spectroscopy to monitor lipid alterations 24 h following coronary occlusion in dogs, and to correlate these finds with regional myocardial blood flow (RMBF) measured by radiolabeled microspheres. The dogs were killed, and samples of excised myocardium were studied by high‐resolution1H NMR spectroscopic analysis using solvent suppression in combination with the Hahn spin‐echo pulse sequence. Mobile lipids levels in myocardium with moderate blood flow reduction (28.6 f 7, integral values, arbitrary units; flow 5–50% of control) were significantly elevated compared to the mobile lipid levels in control myocardium (5.3 ± 8,P<0.001) and in myocardium with severe flow reduction (7.2 ± 10,P<0.001; flow 5% of control). The mobile lipids in myocardium with severe flow reduction were not elevated significantly relative to control tissue. As anticipated, depression in the level of creatine paralleled the microsphere determined degree of ischemia, i.e., compared to control (9.0 ± 3); creatine levels were moderately decreased with flows 5–50% of control (5.5 ± 4,P<0.001) and markedly decreased with flows<5% of control (1.0 ± 2,P<0.001). This study suggests that high‐resolution1H NMR spectroscopy may be used to evaluate alterations in myocardial lipid levels following an ischemic insult. This observation, in addition to changes in other selected metabolites, may provide diagnostic and pathophysiologic insight into the severity of the myocardial injury. © 1987 Ac

ISSN:0740-3194    

DOI:10.1002/mrm.1910050104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY

摘要:

AbstractA general treatment of nuclear magnetic resonance imaging (MRI) and spectroscopic imaging (MRSI), which takes into account the effects of chemical shift, motion, field inhomogeneity, and relaxation times, is presented. A graphical representation based on thektrajectory formalism which includes these effects is then developed for MRI and MRSI acquisition processes. These considerations should be useful in the study and design of flow‐sensitive MRI and MRSI methods and the accurate prediction of motion artifacts in conventional MRI and MRSI techniques. We conclude by presenting examples illustrating applications of the general theory to specific MRSI and flow imaging methods. © 1987 Academic Press, I

ISSN:0740-3194    

DOI:10.1002/mrm.1910050105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY

摘要:

AbstractSeveral pulse sequences which generate projected MR angiograms are presented. These pulse sequences exploit multiple‐gradient refocused echoes to obtain several independent angiograms, which can be combined or separately analyzed to provide more information than an individual angiogram. For example, a series of angiograms, each with a different projection axis, can be obtained in the time required to obtain a single angiogram using a single‐echo method. If the view angle of each echo is the same, then the acquired angiograms can be added to enhance the signal‐to‐noise ratio. Another pulse sequence simultaneously obtains two or more angiograms, sensitive to orthogonal flow components of the overall blood flow. These angiograms are then added to give an angiogram which is sensitive to flow in all directions. © 1987 Academic Pr

ISSN:0740-3194    

DOI:10.1002/mrm.1910050106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY

摘要:

AbstractA pulse sequence is presented which uses Polarization Transfer by a Selective Homo‐nuclear Technique (POTSHOT) to retain all resonances, in phase, from a selected coupled spin system while suppressing all other peaks, from both coupled and noncoupled spins. This technique, which is a selective form of Homonuclear Polarization Transfer (HPT), has been used in a 1.5‐T whole‐body system to generate edited1H lactate spectra from lactate/oil phantoms and from excised dog hearts. © 1987 Academic Pres

ISSN:0740-3194    

DOI:10.1002/mrm.1910050107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY

摘要:

AbstractAggregation of human erythrocytes at physiological hematocrit by hydroxyethyl starch (HES) was investigated with a1H nuclear magnetic resonance method which measures the erythrocyte mean water exchange time, τa. A relationship that takes into account the effect of the aggregate as the water‐exchanging unit was used to transform τ. values into the number of cells per aggregate,n. The procedure permits the determination of the time course of aggregation as well as its initial and equilibrium status. The values ofnat equilibrium range from about 2 to 4 cells over the concentration of 1 to 5% HES in isotonic saline. The aggregation of erythrocytes in the presence of HES was found to follow first‐order kinetics. The feasibility of this technique for application in the study of diseased states is indicated. © 1987 Academic Pres

ISSN:0740-3194    

DOI:10.1002/mrm.1910050108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY

摘要:

AbstractNitroxides, paramagnetic compounds with demonstrated effectiveness as contrast agents in proton magnetic resonance imaging, shorten the relaxation times of protons and therefore cause an increase in image intensity in tissues into which they distribute. In this study, the metabolic fate of the nitroxide moiety was examined in the dog using a pyrrolidine nitroxide derivative, 2,2,5,5‐tetramethylpyrrolidine‐l‐oxyl‐3‐carbxylic acid, for which contrast‐enhancing properties have been previously studied in animals. After radiolabeling by microwave discharge in the presence of tritium gas, the compound was administered intravenously to a dog. Ninety‐four percent of the radioactivity injected was recovered in urine within 3 days; the majority (90%) was excreted during the first 6 h. The radioactivity in the urine was identified as either the unchanged nitroxide or its corresponding hydroxylamine. Neither complete reduction of the nitroxide moiety to the amine nor any other metabolic transformation was observed. © 1987 Acade

ISSN:0740-3194    

DOI:10.1002/mrm.1910050109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY

摘要:

AbstractApparent31P spin–lattice relaxation times have been measuredin vivofor brain phosphates in young adult, mature adult, and aged rats at 4.7 T and 35°C. Statistically significant differences were found for most phosphate species, except PCr and y‐ATP, among the three age groups, particularly between the young and mature adults. Age‐related changes in tissue composition and exchange reactions are discussed as possible contributors to these results. © 1987 Academic Pre

ISSN:0740-3194    

DOI:10.1002/mrm.1910050110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY

摘要:

AbstractA method to obtain separate cross‐sectional NMR images of chemically different species on the basis of their difference in chemical shift is presented. The total experiment time is no longer than that required for a conventional image and the method retains the full sensitivity of a spin‐echo 2DFI imaging experiment. Simple addition of the chemical‐shift selective images produces an image free from chemical‐shift artifacts. Results of anin vivoexperiment on a human subject are presented. © 1987 Academic pr

ISSN:0740-3194    

DOI:10.1002/mrm.1910050111

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1987

数据来源: WILEY