摘要:

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 Pres

ISSN:0740-3194    

DOI:10.1002/mrm.1910110102

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

年代:1989

数据来源: WILEY

摘要:

AbstractA statistical analysis system for classifying normal brain tissue has been applied to the analysis of MRI scans on 45 volunteers. The Bayes Maximum Likelihood method was used to achieve a discrimination accuracy of 84% for 13 tissue types among three age group sets, with classification accuracies for individual regions ranging from 50 to 100%. In order to attain this level of discrimination a set of seven derived relaxation‐type parameters was used to categorize the tissue types. Values for these experimentally estimated parameters were derived from the MRI intensities of eight images in the following pulse sequences: (1) a Carr‐Purcell‐Meiboom‐Gill (CPMG) four‐echo train, (2)a single‐echo inversion recovery, and (3) three single‐echo sequences with varying repetition times, TR, and echo delays, TE. TheT2values derived from ratios of single‐echo intensities showed better discrimination power than those from the four‐echo CPMG train. The general precision of the seven estimated parameters was excellent, with percentage stan‐ dard deviations ranging from 4 to 18% for the various regions studied. The tissue discrimination achieved by use of just three relaxation parameters,T1,T2, and proton density, calculated from intensities of images from a four‐echo sequence, an inversion recovery sequence, and a short TR single‐echo sequence, was not as good, being only 55%. ©

ISSN:0740-3194    

DOI:10.1002/mrm.1910110103

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

年代:1989

数据来源: WILEY

摘要:

AbstractA three‐dimensional Fourier transform magnetic resonance imaging technique is presented. This procedure can be used to selectively detect flowing material such as blood in arteries and veins. Since flow is detected in a manner in which velocity‐induced phase shifts are compensated, signal loss arising from complex flow and turbulence is minimized. The flow image is sensitive to all velocity components of flow. Applications this technique are limited, however, to relatively straight vessels having appreciable flow. Examples of application of this technique to healthy and diseased carotid arteries shown. © 1989 Academic Press,

ISSN:0740-3194    

DOI:10.1002/mrm.1910110104

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

年代:1989

数据来源: WILEY

摘要:

AbstractHigh‐resolution proton NMR spectra of normal human brainin vivohave been obtained from selected 27‐ and 64‐ml volumes‐of‐interest (VOI) localized in the insular area, the occipital area, the thalamus, and the cerebellum of normal volunteers. Localization was achieved by stimulated echo (STEAM) sequences using a conventional 1.5‐T whole‐body MRI system (Siemens Magnetom). The proton NMR spectra show resonances from lipids, lactate, acetate, Nacetylaspartate (NAA), γ‐aminobutyrate, glutamine, glutamate, aspartate, creatine and phosphocreatine, choline‐containing compounds, taurine, and inositols. WhileT1relaxation times of most of these metabolites were about 1100–1700 ms without significant regional differences, theirT2relaxation times varied between 100 and 500 ms. The longestT2values of about (500 ± 50) ms were observed for the methyl protons of NAA in the white matter of the occipital lobe compared to (320 ± 30) ms in the other parts of the brain. No significant regionalT2differences were found for choline and creatine methyl resonances. The relative concentrations of NAA in gray and white matter were found to be 35% higher than those in the thalamus and cerebellum. Assuming a concentration of 10 mMfor total creatine the resulting NAA concentrations of 13–18 mMare by a factor of 2–3 higher than previously reported using analytical techniques. Cerebral lactate reached a maximum concentration of about 1.0 mM.

ISSN:0740-3194    

DOI:10.1002/mrm.1910110105

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

年代:1989

数据来源: WILEY

摘要:

AbstractIn this study, we used31P NMR to investigate the relationship between cardiac work load and creatine kinase flux in intact pigs. NMR measurements were performed on anesthetized miniature swine in which a surface coil was surgically implanted on the surface of the left ventricle. Cardiac workload was varied by infusion of norepinephrine. Phosphate exchange between creatine phosphate and ATP was measured by a combined saturation transfer, saturation recovery pulse sequence. Exchange measurements showed that creatine kinase flux and concentrations of PCr and ATP were independent of workload for a 2.5‐fold range of cardiac rate‐pressure products. It appears that, if creatine kinase flux is coupled to work load, the pig heart operates in a regime where small changes in metabolite concentrations or creatine kinase flux are sufficient to maintain elevated workloads. Exchange and relaxation measurements, at 2.0 and 4.7 T, yieldedT1relaxation times for creatine phosphate and ATP which are longer than most reported values. Analysis of the T1data indicates that chemical‐shift anisotropy is a plausible mechanism for a portion of the spin‐lattice relaxation rate at high field strengths. © 1989 Academic Pr

ISSN:0740-3194    

DOI:10.1002/mrm.1910110106

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe use of a water‐suppressing spin‐echo pulse sequence reported recently (V. Sklenar and A. Bax,J. Magn. Reson.74, 469 (1987); M. von Kienlin, M. DeCorps, J. P. Albrand, M. F. Foray, and P. Blondet,J. Magn. Reson.76, 169 (1987)) was evaluated forin vivobrain proton surface coil NMR spectroscopy. The studies were performed on cat brain using surface coils at 4.7 T. The sequence produced brain spectra with adequate water suppression, and a broader excitation profile than sequences which form spin echoes using 1331 pulses (P. J. Hore,J. Magn. Reson.54, 539 (1983); H. P. Hetherington, M. J. Avison, and R. G. Shulman,Proc. Natl. Acad. Sci. USA82, 3115 (1985)). The phase artifacts were smaller than those produced in 1331 methods, but theoretical analysis showed they should not be completely absent. The effectiveness of lengthening the spin‐echo delay in the new sequence for suppression of unwanted lipid resonances was demon‐strated. The sequence was shown to be capable of detecting lactate formation and clearance in a global cerebral ischemia experiment. © 1989 Academic

ISSN:0740-3194    

DOI:10.1002/mrm.1910110107

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

年代:1989

数据来源: WILEY

摘要:

AbstractA postprocessing linear filter was applied to spin‐echo images on 10 patients with known or suspected chest wall invasion due to bronchogenic carcinoma. This technique known as eigenimage filtering allows selective feature extraction of suspected abnormali‐ties from conventional MR images. The final result is an image with marked increased contrast range through enhancement of a desired process (tumor) with suppression of an interfering process (e.g., normal surrounding tissue). This preliminary work demon‐strates the ease with which the technique may be implemented, the contrast enhancement obtained between the desired and the interfering feature in the final eigenimage, and its ability to correct for partial volume averaging effects. Also demonstrated are artifacts that can interfere with the interpretation of the eigenimage and a method for minimizing these artifacts in the final eigenimage. © 1989 Academic Pres

ISSN:0740-3194    

DOI:10.1002/mrm.1910110108

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe concept of temporal echo multiplexing is defined and used to develop rapid bipha‐sic spin‐echo sequences for imaging the heart. Three imaging sequences, based on four‐echo and two‐echo multiplexing and rapid single echo (i.e., conventional spin‐echo imaging), are compared. Preliminary results indicate that two‐echo multiplexing yields a significantly reduced acquisition time window with image quality that is only slightly inferior to single‐echo imaging. Single‐echo biphasic imaging results in the most consistent image quality. © 1989 Aca

ISSN:0740-3194    

DOI:10.1002/mrm.1910110109

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

年代:1989

数据来源: WILEY

摘要:

AbstractMost magnetic resonance imaging (MRI) techniques are subject to a “motional blurring” arising from the acquisition of data in the presence of a frequency‐encoding gradient. The Fourier transform of the signal from a spin moving along a magnetic field gradient obeys an equation analogous to the free space Schrijdinger equation. Computer simulations of the Bloch equations illustrate the implications of this motional blurring in MRI. © 1989 Academic Pres

ISSN:0740-3194    

DOI:10.1002/mrm.1910110110

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe thermodynamic and kinetic parameters of the reaction catalyzed by creatine kinase (CK) were measuredin vitroin the temperature range 13 to 35°C, using31P NMR spectroscopy, including magnetization transfer methods. The apparent equilibrium constant of the reaction and the associated enthalpy for the formation of ATP at 35°C, pH 8.2, and excess [Mg2+] were 3.5 × 109M−1and −2.4 ± 0.5 kcal/mol, respectively. The rates at equilibrium at 35°C catalyzed by 1 unit/ml CK were 12.4 and 10.7 μM /s at pH 7 and 8, respectively. The rate constants per 1 unit CK/ 1 ml at 35°C, pH 7, were 1.3 × 108s−1M−2and 9.9 × s−1M−1in the direction of ATP and PCr formation, respectively. The activation energies in both directions were similar and corresponded to 15 ± 2 kcal/mol at pH 7 and 17.5 ± 1.5 kcal/mol at pH 8. Comparison ofin vivoresults with the abovein vitrodata may provide information regarding the activity and kinet

ISSN:0740-3194    

DOI:10.1002/mrm.1910110111

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

年代:1989

数据来源: WILEY