摘要:

AbstractNoninvasive monitoring of the effects of treatment on cancer tissue is fundamental to the development of rational radioimmunotherapy (RIT) schemes employing radiolabeled monoclonal antibodies or antibody fragments specific for human cancer. Recent advances in nuclear magnetic resonance spectroscopy make it an attractive candidate for sequential, topical monotoring by31P NMR of metabolic events during RIT. Preliminary to this effort, we examined the metabolic competence of the well‐characterized, murine KHJJ tumorin situin BALB/c mice using31P surface‐coil NMR. The ATP/Piratio in tumor volumes ranging from 100 to 800 mm3showed that tumors over this range of sizes were able to maintain high levels of ATP relative toPi. As the tumor volume increased above 1 cm3, ATP/Pilevels indicated poor metabolic competence. This lack of metabolic competence was correlated with histological evidence of tissue necrosis and vascular disintegration. TheT1values of assigned phosphorus metabolites were established. Intracellular pH, as determined from the chemical shift ofPi, was found to vary in these tumors from 7.1 in rapidly metabolizing tissue to 6.6 in necrotic tumors.© 1985 Academic Press

ISSN:0740-3194    

DOI:10.1002/mrm.1910020502

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

年代:1985

数据来源: WILEY

摘要:

AbstractA method of chemical‐shift imaging is described using the invariance of chemical shifts to changes in magnetic field gradients used for frequency encoding of position in imaging. This enables separation of the effects on the observed signal of chemical shift from the effects of different positions along the imaging gradient when the signal is observed with different gradients. A simple implementation for a two‐line spectrum is presented using signals observed with normal and reversed imaging gradients. This is used to create “fat” and “water” images of the thigh.© 1985 Academ

ISSN:0740-3194    

DOI:10.1002/mrm.1910020503

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

年代:1985

数据来源: WILEY

摘要:

AbstractThe echo‐planar imaging method (EPI) and its variants can acquire data sufficient to form an image in a much shorter time than the Fourier or projection‐reconstruction methods. Fundamental requirements on gradient waveforms and signal sampling are discussed for EPI and SEPI (a variant using sinusoidal gradient waveforms), based on thek‐trajectory formulation of acquisition in NMR imaging. Using a new simulation method, image defects in EPI and SEPI are demonstrated which result from failure to meet these requirements. Faithful rendition of theoretically ideal gradient waveforms places severe demands on gradient system response in rapid imaging. It is shown, however, that nonideal gradient system response need not degrade images if appropriate reconstruction computations are used. Transfer functions and noise power spectra are derived for EPI and SEPI, and the ratio of these two functions is used to derive ideal observer signal‐to‐noise ratios for simple visual interpretive tasks. It is shown that ideal observer performance can differ significantly between EPI and SEPI for some visual tasks, using the same NMR imaging system.© 1985 Academic

ISSN:0740-3194    

DOI:10.1002/mrm.1910020504

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

年代:1985

数据来源: WILEY

摘要:

AbstractBecause polarization transfer from one type of nucleus to another can occur only when both types of nuclei are excited, it is possible, by using two separate rf coils for the excitation, to restrict the spatial region of the sample from which a signal can be received to a specific volume of overlap of the two inhomogeneous field patterns. In this paper we develop the theory of this method of localization in a homogeneous static field. The polarization transfer is achieved by a generalized phase‐cycled DEPT sequence, in which case the method has the additional advantage of a gain in sensitivity of a13C signal associated with the maximum polarization‐transfer enhancement. Localization by means of the inverse‐DEPT sequence is also studied, and off‐resonance effects are calculated. Experimental confirmation of the theoretical expressions is given.© 1985 Academic P

ISSN:0740-3194    

DOI:10.1002/mrm.1910020505

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

年代:1985

数据来源: WILEY

摘要:

AbstractAn effective shield for the de fringing field produced by a large‐bore, high field magnet intended for imaging andin vivospectroscopy is presented. While limiting the extent of fringe fields, the shield has little effect on the homogeneity of the central field of the magnet. The effect of institutional safety policies as well as the exigencies of patient access in a hospital environment are emphasized as influences on the planning of anin vivoNMR installation.© 1985 Academic Press,I

ISSN:0740-3194    

DOI:10.1002/mrm.1910020506

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

年代:1985

数据来源: WILEY

摘要:

AbstractThe echo‐planar shift mapping (EPSM) technique, a variant of echo‐planar imaging (EPI), is evaluated with theoretical studies using computer simulations and with experimental studies using fluorine resonances in phantoms. In situations where the signal‐to‐noise ratio permits, it is shown that EPSM can produce in a few seconds chemical‐shift spectra at all points in a specified spin‐density image corresponding to a selected slice. Applications of this technique are likely to be for proton and fluorine chemical‐shift measurements and rapid studies of magnetic field inhomogeneities produced by magnet nonalignment and field shifts around magnetic materials.© 1985 Academic Press,Inc.© 1985 Aca

ISSN:0740-3194    

DOI:10.1002/mrm.1910020507

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

年代:1985

数据来源: WILEY

摘要:

AbstractThe design of a two‐turn radiofrequency coil for MR imaging at 0.15 T is presented. The use of well‐isolated copper tube (instead of the usual wire) as conductor material resulted in an open, patient friendly construction. Furthermore, theQvalue and signalto‐noise ratio of the tube‐type coil were increased as compared to the corresponding values in the case of a geometrically similar wire‐type coil.© 1985 Academic

ISSN:0740-3194    

DOI:10.1002/mrm.1910020508

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

年代:1985

数据来源: WILEY

摘要:

AbstractIsolated cells can be kept in steady‐state conditions for very long periods of time when inserted into dialysis microfibers and perifused with a nutrient‐containing solution. Using this system, stable31PNMR spectra have been obtained on dog kidney tubules for a period of 13 h.© 1985 Academic Press

ISSN:0740-3194    

DOI:10.1002/mrm.1910020509

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

年代:1985

数据来源: WILEY

摘要:

AbstractMeasuring the NMR relaxation parameters of selectively excited protons within molecules bound to the cell membrane was shown to provide a profitable way of looking at the viruscell interaction. Such approach made it possible to delineate the virus adsorption to human red blood cells by using the NMR features of the cytoskeleton inhibitor colchicine.© 1985 Academic Press,Inc

ISSN:0740-3194    

DOI:10.1002/mrm.1910020510

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

年代:1985

数据来源: WILEY

摘要:

AbstractAn application of the Slepian‐Pollak‐Landau “time and band limited functions” is found in NMR imaging. The precise context is best described by the rotating‐frame dynamics of the Bloch equations, where an analogy is made to the problem of simultaneously concentrating a function in time and frequency. The appropriately modulated rf fields are found to yield excellent response characteristics when used in numerical simulations of the Bloch equations.© 1985 Academic

ISSN:0740-3194    

DOI:10.1002/mrm.1910020511

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

年代:1985

数据来源: WILEY