摘要:

AbstractThe temporal and spatial dependence of the eddy current fields, generated by switching offx, y, andzgradients in a 40‐cm bore Bruker superconducting magnet, have been studied by measuring the offset frequency of the proton FID obtained from a small spherical sample. The measurements were made with the pre‐emphasis unit deactivated. The data obtained at each location were well fitted to a sum of four exponentially decaying components. The shortest decay is, in each case, associated with the decay of the current in the gradient coil itself, while the other decays are associated with three eddy currents with decay times ranging from 13 to 480 ms. Each of the three eddy currents generates an essentially uniform gradient for at least 4 cm on either side of the isocenter. However, when the eddy currents are generated by either the vertical transverse gradient or the longitudinal gradient, the eddy current gradients are also accompanied by a field sh

ISSN:0740-3194    

DOI:10.1002/mrm.1910310112

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

年代:1994

数据来源: WILEY

摘要:

AbstractWe report the first demonstration of EPR spectroscopy to study free radical reactions in live mice and excised muscle tissue resulting from the metabolism of nitrosobenzene. A broad three‐the EPR spectrum (aN= 11.6 G) appeared in the buttocks region of a mouse place in an L‐band loop gap resonator after intramuscular or intraperitoneal injection of 0.2 among nitrosobenzene. The signal intensity reached a maximum at 20 to 30 min and remained constant well beyond 2 h. If muscle tissue was dosed with nitrosobenzene and excised within 5 min, a similar three‐line X‐band EPR spectrum was obtained which was preceded by the rapid growth and subsequent decay of an EPR spectrum identical with that of the phenylhydronitroxide radical, which was presumably generated from reactions between nitrosobenzene and reducing agents in the blood or tissue such as NADH or ascorbic acid. A model system containing nitrosobenzene and unsaturated fatty acids (olive oil or animal fat) yielded an identical three‐line spectrum resulting from radical adducts of nitrosobenzene across the double bond. Overall, these results suggest that the most probable mechanismin vivowas nitrosobenzene covalently adding (“binding”) to polyunsaturated fatty acid clusters in fat

ISSN:0740-3194    

DOI:10.1002/mrm.1910310113

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe effect of off‐resonance preirradiation on proton spectra acquired from the healthy rat brain at 4.7 T is examined using a PRESS sequence. The creatin/phosphocreatine (Cr/PCr) signal at 3.0 ppm decreases in signal intensity for offset frequencies between ±10 kHz. This cannot be explained by RF bleedover, but is attributed to magnetization transfer between two pools of Cr/PCr, one with a longT2relaxation time giving the observed NMR signal, the other corresponding to a broad resonance line being completely or partially saturated by off‐resonance preirradiation. Possible interpretations of these results are discu

ISSN:0740-3194    

DOI:10.1002/mrm.1910310114

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

年代:1994

数据来源: WILEY

摘要:

AbstractA nonwater‐suppressed localized spectroscopy experiment using the PRESS‐sequence has been used to study the signal changes of the water resonance during cortical activation. Significant effects with an effect‐to‐noise ratio up to 50:1 for a single shot experiment have been observed upon photic stimulation. The exceedingly high signal‐to‐noise ratio of the experiment was used to demonstrate signal changes as low as 0.1% after electrical stimulation of the m

ISSN:0740-3194    

DOI:10.1002/mrm.1910310115

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

年代:1994

数据来源: WILEY

ISSN:0740-3194    

DOI:10.1002/mrm.1910310116

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

年代:1994

数据来源: WILEY

ISSN:0740-3194    

DOI:10.1002/mrm.1910310101

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

年代:1994

数据来源: WILEY