摘要:

AbstractThe effects of a static magnetic field (0.75 T) on DNA synthesis and survival were examined with Chinese hamster V79 cells in cultures with and without fast‐neutron irradiation. We found that the magnetic field applied alone for up to several hours did not cause a significant effect in either the rate of DNA synthesis or cell viability; the latter was assayed by colony formation. When cells were exposed simultaneously to the magnetic field and fast neutrons, the effects resembled those observed with neutrons alone. This was the case for both inhibition of DNA synthesis and cell killing. Cells irradiated first with neutrons followed immediately by 1 h of magnetic field exposure showed a dose‐survival response curve indistinguishable from that of neutrons alone. These data suggest that the biological effect due to the magnetic field is negligible and that the presence of the magnetic field either during or subsequent to fast‐neutron irradiation does not affect the neutron‐induced radiation damage or its repair. © 1987 Academic Pr

ISSN:0740-3194    

DOI:10.1002/mrm.1910050402

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

年代:1987

数据来源: WILEY

摘要:

AbstractThe “prescan” process for setting the gain of an MRI scanner can be confounded by an effect arising from the spatial variation of the angle between the vector reception field of a local or surface coil and the excitation field of a whole‐body coil. It is most pronounced when the phase‐encoding direction is parallel to the plane of the coil but not along the magnetic field. The largest signal is shown to reside in a data row that is shifted from the one that corresponds to zero phase‐encoding gradient. The effect depends on the field‐of‐view and the dimensions of the receiving coil. Strategies are suggested by which manufacturers of scanners can cope with this intrinsic problem. In the meantime, users of surface coils should be aware of the difficulty. © 1987 Acade

ISSN:0740-3194    

DOI:10.1002/mrm.1910050403

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

年代:1987

数据来源: WILEY

摘要:

AbstractSince 1/T2of protons of tissue water is generally much greater than 1/T1at typical imaging fields, small single‐ion contrast agents–such as Gd(DTPA), which make comparable incremental contributions and therefore smaller fractional contributions to 1/T2compared to 1/T1–are not as desirable for contrast‐enhancement as agents that could enhance 1/T2preferentially. In principle, such specialized agents will only be effective at higher fields because the field dependence (dispersion) of 1/T1is such that it approaches zero at high fields whereas 1/T2approaches a constant value. The residual 1/T2is called the “secular” contribution and arises from fluctuations in time–as sensed by the protons of diffusing solvent or tissue water molecules–of the component of the magnetic field parallel to the static applied field. For solutions or suspensions of sufficiently large paramagnetic or ferromagnetic particles (⋧250 Å diameter), the paramagnetic contributions to the relaxation rates satisfy 1/T2≫ 1/T1at typical imaging fields. We examine the theory of secular relaxation in some detail, particularly as it applies to systems relevant to magnetic resonance imaging, and then analyze the data for solutions, suspensions, or tissue containing ferritin, erythrocytes, agar‐bound magnetite particles, and liver with lowdensity composite polymer‐coated magnetite. In most cases we can explain the relaxation data, often quantitatively, in terms of the theory of relaxation of protons (water molecules) diffusing in the outer sphere environments of magnetized particles. The dipolar field produced by these particles has a strong spatial dependence, and its apparent fluctuations in time as seen by the diffusing protons produce spin transitions that contribute to both 1/T1and /T2comparably at low fields, for the larger particles, because of dispersion, the secular term dominates at fields of interest. On the basis of the agreement of theory with data for solutions of small paramagnetic complexes, large magnetite particles, and liver containing low‐density polymer‐coated magnetite agglomerates, it is argued that the theory is sufficiently reliable so that, e.g., for ferritin–for which 1/T2is unexpectedly large–the source of its large relaxivity must reside in nonideal chemistry of the ferritin core. For blood, it appears that diffusion through intracellular gradients determines

ISSN:0740-3194    

DOI:10.1002/mrm.1910050404

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

年代:1987

数据来源: WILEY

摘要:

Abstract31NMR spectroscopy was used to study renal allografts in rats subjected to allograft rejection, cyclosporine toxicity, ischemia, and ureteral obstruction. Parameters of relative peak areas and intracellular pH were accurately distinguished among the different causes of graft dysfunction. Ureteral obstruction was clearly identified by elevations in the phosphodiester/urine phosphate peak. Ischemia and rejection were. both associated with increases in inorganic phosphates and phosphomonesters and decreases in the β‐phosphate peak of adenosine triphosphate but were distinguishable from each other by differences in intracellular pH which was normal in rejected allografts (7.33 ± 0.07,n= 3) but low in ischemic allografts (7.00 ± 0.05,n= 3,P<0.05). Grafts insulted with cyclosporine toxicity were not distinguishable from normal allografts by any of the parameters studied. These data suggest that31P NMR spectroscopy may have potential clinical application in differentiating among the causes of graft failure of human rend allografts. © 1987 Academic Press

ISSN:0740-3194    

DOI:10.1002/mrm.1910050405

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

年代:1987

数据来源: WILEY

摘要:

AbstractIn vivo1H NMR spectral editing techniques were used to monitor cerebral lactate production during remotely controlled temporary forebrain ischemia in rats. The lactate/N‐acetylaspartate (NAA) ratio correlated with survival after ischemia and subsequent reperfusion. The lactate/NAA ratio that predicted death after ischemia in rats was estimated to be approximately 1.3. © 1987 Academic Press, I

ISSN:0740-3194    

DOI:10.1002/mrm.1910050406

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

年代:1987

数据来源: WILEY

摘要:

AbstractThis study examines slice selection and diffusion as sources of systematic error inT2estimates obtained from imaging experiments. The selective refocusing pulses in a multislice, two‐echo, spin‐warp experiment cause slice profiles of sequential echoes to change in shape. This results in bias inT2images calculated from the two‐echo data set. A method to correct the bias is presented. The effect of diffusion onT2images obtained with typical two‐echo imaging sequences was found to be negligible. © 1987 Academic Pr

ISSN:0740-3194    

DOI:10.1002/mrm.1910050407

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

年代:1987

数据来源: WILEY

摘要:

AbstractExpressions for the contrast‐to‐noise (C/N) behavior in images obtained from rapid low flip‐angle excitation pulses are derived, taking into account bothT1‐ andT2‐dependent contrasts. It is shown, and demonstrated experimentally, that images withT2‐weighted contrasts can be efficiently acquired with such sequences, by a suitable choice ofTR,TEand tip angle. © 1987 Academi

ISSN:0740-3194    

DOI:10.1002/mrm.1910050408

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

年代:1987

数据来源: WILEY

摘要:

AbstractGiven current clinical use of phospholipid bilayer structures (liposomes/vesicles) as non‐toxic drug delivery vehicles, we have addressed the possibility of employing the phospholipids themselves as MRI contrast agents. To this end we have synthesized phosphatidylcholine with a nitroxide spin label replacing one methyl residue of the choline headgroup. This material was mixed with natural phosphatidylcholine in mole ratios from 150 to 1:1 and used to prepare sonicated unilamellar vesicles in saline. Expected structural features of these vesicles were verified by freeze‐fracture electron microscopy. ProtonT1values of saline were readily decreased to less than 0.3 s by such preparations, yielding a net relaxivity of 0.6M−1s−1. The approach seems to be a realistic way of firmly associating a contrast agent of minimal toxicity with ordinary liposomes/vesicles in a manner that is not subject to leakage. © 1987 Academic Pr

ISSN:0740-3194    

DOI:10.1002/mrm.1910050409

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

年代:1987

数据来源: WILEY

摘要:

AbstractIn vivoNMR has focused on using31P and1H to study metabolism in humans. Comparable31C NMR studies have not been undertaken, presumably, because of its insensitivity. We report herein that the natural abundance13C signal from C1glycogen is observable. The ability to observe the signal opens new opportunities to noninvasively study glycogen metabolism in man. © 1987 Academic Press, Inc

ISSN:0740-3194    

DOI:10.1002/mrm.1910050410

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

年代:1987

数据来源: WILEY

摘要:

AbstractThe RARE method is based on the principle of echo imaging to generate images with highT2contrast. Since RARE is a fast imaging method, it can be used to acquire a high‐resolution three‐dimensional data set in less than 15 min. Thin slices from such a three‐dimensional data set provide detailed information about the ventricular system. © 1987 Academic Pres

ISSN:0740-3194    

DOI:10.1002/mrm.1910050411

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

年代:1987

数据来源: WILEY