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Streitwieser A Keevil TA Taylor DR Dart EC 《Journal of the American Chemical Society》2005,127(25):9290-9297
Kinetic acidities are reported for methane, ethane, propane, cyclopropane, isobutane, neopentane, tetramethylbutane, norbornane, nortricyclene, and adamantane by tritiodeprotonation or deuteriodeprotonation in cyclohexylamine catalyzed by cesium cyclohexylamide. 相似文献
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The performance of volume selection sequences for in vivo NMR spectroscopy: implications for quantitative MRS. 总被引:1,自引:0,他引:1
Previous work has demonstrated that deficiencies in volume selection sequences used in magnetic resonance spectroscopy may compromise the quality of the spectra obtained. In this paper, further studies on the ISIS and PRESS sequences are presented. Under conditions of partial saturation, ISIS can exhibit serious contamination with extraneous signal, particularly when a small volume of interest (VOI) is selected. ISIS protocols should therefore use VOIs that are large relative to the target volume, and repetition times that are as long as practicable. In PRESS, contamination is found to be minimised by using a VOI that is small relative to the target volume, and to be independent of repetition time. PRESS performance is also independent of echo time, except when very short echo times are used. These results are consistent with previously published work on ISIS and PRESS, and it is now possible to establish generic features of these sequences and to understand the implications for quantitative spectroscopy. T(1)-weighting of contamination in ISIS can compromise both relative and absolute quantification techniques in several respects. Contamination in PRESS is largely independent of relaxation times and would be easier to model and correct for in the context of quantitative spectroscopy. 相似文献
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Brown J Buckley D Coulthard A Dixon AK Dixon JM Easton DF Eeles RA Evans DG Gilbert FG Graves M Hayes C Jenkins JP Jones AP Keevil SF Leach MO Liney GP Moss SM Padhani AR Parker GJ Pointon LJ Ponder BA Redpath TW Sloane JP Turnbull LW Walker LG Warren RM 《Magnetic resonance imaging》2000,18(7):765-776
The imaging and analysis protocol of the UK multicentre study of magnetic resonance imaging (MRI) as a method of screening for breast cancer in women at genetic risk is described. The study will compare the sensitivity and specificity of contrast-enhanced MRI with two-view x-ray mammography. Approximately 500 women below the age of 50 at high genetic risk of breast cancer will be recruited per year for three years, with annual MRI and x-ray mammography continuing for up to 5 years. A symptomatic cohort will be measured in the first year to ensure consistent reporting between centres. The MRI examination comprises a high-sensitivity three-dimensional contrast-enhanced assessment, followed by a high-specificity contrast-enhanced study in equivocal cases. Multiparametric analysis will encompass morphological assessment, the kinetics of contrast agent uptake and determination of quantitative pharmacokinetic parameters. Retrospective analysis will identify the most specific indicators of malignancy. Sensitivity and specificity, together with diagnostic performance, diagnostic impact and therapeutic impact will be assessed with reference to pathology, follow-up and changes in diagnostic certainty and therapeutic decisions. Mammography, lesion localisation, pathology and cytology will be performed in accordance with the UK NHS Breast Screening Programme quality assurance standards. Similar standards of quality assurance will be applied for MR measurements and evaluation. 相似文献
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I motivate and discuss non-minimal and non-universal models of supersymmetry and supergravity consistent with string unification
at 1010 GeV. 相似文献
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E. Schaefer F. M. Schemjakin W. A. Wolkowa A. K. Babko I. Martyntschenko A. Schimko B. B. Dey S. Rengachari M. V. Sitharaman J. Rzymkowski T. M. Kolthoff G. L. Maheshwari J. B. Tha T. Ilahi A. Rohmann B. Singh T. I. Malik S. Kilpi B. B. Owen Louise Foering H. E. Bent N. B. Keevil Ch. K. Ingold H. G. G. Mohrhenn E. Cattelain C. Couchet 《Analytical and bioanalytical chemistry》1941,122(9-10):354-368
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