ISSN:0740-3194    

DOI:10.1002/mrm.1910170102

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe performance of the rotating frame localization method is discussed, with emphasis on performing the experiment and processing the data in the optimum manner. Studies on phantom samples are presented to illustrate various imperfections which affect the confidence that can be placed on acquired data. © 1991 Academic Press, Inc

ISSN:0740-3194    

DOI:10.1002/mrm.1910170103

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

年代:1991

数据来源: WILEY

摘要:

AbstractA simple high‐pass cavity resonator has been constructed for NMR imaging use at 500 MHz. A capacitative circuit arrangement is used to drive the device. A novel split‐coil or half‐resonator design is also introduced for lower‐frequency operation with applications in whole‐body medical imaging. © 1991 Academic

ISSN:0740-3194    

DOI:10.1002/mrm.1910170104

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

年代:1991

数据来源: WILEY

摘要:

AbstractActive magnetic screening allows the production of gradient coils which are magnetically decoupled from their surroundings. Using such coils the eddy current problems associated with the generation of large, rapidly switched gradients within the confines of a superconductive magnet can be eliminated. In this paper the principles of active screening are outlined and some of the methods of designing screened gradient coils are described. Problems relating to the construction of screened gradient coils are also addressed. © 1991 Academic Press, Inc

ISSN:0740-3194    

DOI:10.1002/mrm.1910170105

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

年代:1991

数据来源: WILEY

摘要:

AbstractIt is shown that a passive magnetic shield for a 1,5‐T whole‐body magnet requires about 20 tons of iron. Moreover, to first order, the amount of shielding material is independent of the radius of the shield. The choice between a thick shield fitting tightly round the magnet and a thinner shield of larger radius is determined by considerations of available space and the need for the highest uniformity of field in the bore. Very high permeability materials such as mu‐metal are useful only in special circumstances. Multiple shields are valuable if a high degree of shielding is required, but the spacing between the shields needs careful attention. Although exact reciprocity of internal and external shielding is not found in the general case, the degree of shielding will be of the same order in both cases. The complete behavior of cylindrical shields around superconducting magnets can be determined by analytical solution of Maxwell's equations; for less regular shapes, solutions may be determined numerically by computer. © 1991 Academic Pres

ISSN:0740-3194    

DOI:10.1002/mrm.1910170106

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe evolution of MRI magnets is reviewed. New magnet developments are discussed with reference to improved performance, novel system features, and lower cost. © 1991 Academic Press, Inc

ISSN:0740-3194    

DOI:10.1002/mrm.1910170107

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

年代:1991

数据来源: WILEY

摘要:

AbstractRecently, we introduced a new numerical approach to the design and optimization of NMR selective pulses, which we have christened “SPINCALC” (J. T. Ngo and P. G. Morris,Biochem. Soc. Trans.14, 1271 (1986); J. T. Ngo and P. G. Morris,Magn. Reson. Med.5, 217(1987)). The first practical application of pulses generated by SPINCALC is demonstrated on a standard 0.5‐T clinical MRI system. Results are shown for single phase π pulses suitable both for selective inversion and for selective refocusing. The extension of SPINCALC to multidimensional pulses is illustrated by the design of a two‐dimensional π pulse. © 1991 Academic

ISSN:0740-3194    

DOI:10.1002/mrm.1910170108

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

年代:1991

数据来源: WILEY

摘要:

AbstractTo investigate the high‐energy phosphate metabolic correlates of left ventricular (LV) dysfunction during the onset and recovery from severe, global myocardial ischemiain 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/dtmaxfell 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). Simultaneous31P 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 topical31P NMR‐S can be performed in th

ISSN:0740-3194    

DOI:10.1002/mrm.1910170109

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

年代:1991

数据来源: WILEY

摘要:

AbstractPhosphorus‐31 liver spectra were recorded from 6 controls and 12 patients with liver disease using TR values of 0.5 and 5 s and a pulse angle of 45°. One of the control subjects was also examined at seven TR values ranging from 0.5 to 20 s. Spectra from one additional patient were collected at TRs of 0.5, 1, and 2 s only. There was a significant increase in the mean ratio of peak areas phosphomonoesters (PME)/β‐ATP in 9 of the 13 patients and a decrease in phosphodiesters (PDE)/β‐ATP in 3 of the patients, compared with controls, at the longer TR values. The saturation factors for PME and PDE were greater than those forPiand β‐ATP, and spectral abnormalities in disease were often more evident as the TR value was increased from 0.5 to 5 s. Acquisition parameters need to be chosen with a knowledge of the impact that saturation effects have on metabolite quantification and Spectral Contrast. © 1991 Academi

ISSN:0740-3194    

DOI:10.1002/mrm.1910170110

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

年代:1991

数据来源: WILEY

摘要:

AbstractWe here report the analysis of single rabbit lenses under high‐glucose stress using four‐dimensional13C nuclear magnetic resonance (NMR) spectroscopy (three spatial and one chemical‐shift). We have produced spatial maps of lenticular metabolites (glucose, sorbitol, and lactate) with submillimeter in‐plane resolution. The production of sorbitol and its inhibition are also presented. This is the first study to report regional tissue metabolism. We expect further improvements in spatial resolution and acquisition times that will enable localized kinetic studies in intact tissues. © 1991 Academic Pr

ISSN:0740-3194    

DOI:10.1002/mrm.1910170111

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

年代:1991

数据来源: WILEY