Triple rule-out

CT Angiography 102 .3.2 Triple Rule-Out 104 .3.3 Hepatic Multi-Phasic Imaging .3.4 Major Trauma Scanning 105 .3.5 Perfusion Studies 105... 

Haidary A, Bis K, Vrachiolitis T, Kosuri R, Balasubramaniam M (2007) Enhancement performance of a 64-slice triple rule-out protocol vs 16-slice and 10-slice multidetector CT-angiography protocols for evaliration of aortic and pulmonary vasculature. J Comput Assist Tomogr 31 917-923... 

Latest multi-detector-row spiral computed tomography (MDCT) scanners are able of such an one-stop-strategy . Cardiac imaging can be incorporated into established examination standard operating procedures for non-cardiac vascular and non-vascular imaging of chest disorders. This approach can be summarized with the buzzword triple rule-out (Gallagher and Raff 2008). 

This model does not say anything about the mechanism of triple-helix formation, because even in the case of an AON mechanism, nucleation may take place at many positions of the chains and may lead to products the chains of which are staggered. The AON model is based on the assumption that these products are too instable to exist in measurable concentration. As already mentioned, Weidner and Engel142 succeeded in proving by relaxation measurements of al CB2 that the kinetics of in vitro triple-helix formation is governed by more than one relaxation time. This rules out an AON mechanism, but the fitting to the experimentally found equilibrium transition curves nevertheless showed good accommodation and AH° computed from these curves could be confirmed by calorimetric measurement. 

However, the observations of Ward and Sherman need not rule out triple-bond participation and vinyl cations in the systems studied by Hanack and co-workers (75-79). Presumably, the enol formate 61 itself arises via a transition state involving a rate-determining protonation and vinyl cation 62 (see previous section). A vinyl cation such as 62 with an adjacent phenyl group is considerably more stable and hence more accessible than a vinyl cation such as 63, stabilized only by a neighboring alkyl group. Hence, formation of enol formate 61 and its... 

This disadvantage can be ruled out by spacers between the allylic and the acrylic group [15], but the selectivity in favor of the allylic group is not improved. An acetylenic triple bond instead helps to clarify the situation. 2-Propynoxyethyl acrylate, available in 90 % yield from ethoxylated propargylic alcohol by esterification, is hydrosilylated very smoothly only at the triple bond, leaving the acrylic side virtually untouched (Eq. 5). 

Practical systems based on Eq. (66), but using Ni(COD)2/RNC mixtures, were reported. Catalysis via Ni(CNR)3 or Ni(CNR)2 intermediates could not be completely ruled out in these cluster systems. The nickel isonitrile and acetylene clusters did not effect hydrogenation of the triple bond in nitrogen (394). 

A dissociative elimination-addition pathway has also been proposed to account for the kinetics of alkaline hydrolysis of 2,4-dinitrophenyl 4 -hydroxyphenylpropionitrile in 40% (v/v) dioxane-water, although participation of the associative Bac2 mechanism cannot be ruled out since it may be facilitated by the electronic effect of the triple bond. Formation of intermediate (15), having a conjugated and cumulated double-bond system, should favour the ElcB mechanism and thereby account for the contrasting entropies of activation found for hydrolysis of (14) and the corresponding 4 -methoxyphenylpropionate. 

The nature of the triple bond requires that the four carbon atoms of this molecule lie in a straight line (bond angle = 180 ), which rules out the possibility of diastereomers. 

Rings are often difficult to rule out on the basis of chemical shifts alone, but the spin couplings would be difficult to explain. Let us consider a triple bond. 

Both planar and boat conformations for 1,4-cyclohexadiene and its derivatives are possible. Addition of Eu(fod)3 allowed the determination of the conformation of 1,4-dihydrobenzyl alcohol [41]. Addition of Eu(fod)3 and double and triple irradiation experiments made the determination of coupling constants possible. The vicinal coupling constants 73,4 and 73,4/ were equal indicating planarity of the ring. Other coupling constants also indicated a planar conformation for the ring. Possible rapid boat-to-boat inversion was ruled out by measurement of coupling constants of 3-fluoro- 1,4-dihydrobenzyl alcohol-d2 from unaltered spectra and spectra obtained after addition of Eu(fod)3. 

A 42-year-old woman with a renal transplant taking triple immunosuppression (azathioprine, ciclosporin, and glucocorticoids) was converted after 7 years from azathioprine plus ciclosporin to mycophenolate (2 g/ day) because of ciclosporin nephrotoxicity (15). Within 2 months she had developed severe persistent watery diarrhea (5-10 stools/day) and lost 7 kg over 2 months. Investigations ruled out an infectious cause and there were features of duodenal villous atrophy on histological examination. Diarrhea disappeared after mycophenolate withdrawal and two subsequent duodenal biopsies showed improvement 2 months later and further complete recovery 6 months later. 

By classical" addition mechanisms, we include the large number of mechanisms advanced to date to rationtdize various aspects of the bromination of double and triple bonds. The major reaction deduced thus far, conversion of the triple bond to a dibromo double bond, cotild be a very localized process. Yet the triple and double bonds of the backbone are in an extended conjugated system and do not have the energetics of the isolated systems. It is not possible to rule out such mechanisms at present. 

A few informative properties of life come from easy category distinctions, such as the fact that all known life makes essential use of carbon and carbon-oxygen-nitrogen molecules in liquid water solution. The seemingly trivial observation that such carbaquist chemistry is ruled out if astrophysical carbon abundance lies below a certain threshold enabled Hoyle [1] to predict the 7.6 MeV carbon-12 ( C) nuclear resonance with remarkable precision because the discovery of the triple-alpha reaction synthesis of in stars happens to be a bottleneck for stellar nucleosynthesis of all the heavy elements. The pragmatic information in this prediction is easy to measure because it guided experimental characterization of nuclear structure where the existing computational capabilities could not. Similar sensitive dependence of the physical state of water has been used to define a habitable zone in planetary physics [10], which is not predictive in the same sense as carbon abundance (we already knew where the earth s orbit lies), but which creates a useful filter in the search for extraterrestrial life. 

Additional work may clarify whether this rather bleak assessment is entirely correct. While selection of a single index experiment is inconsistent with the observations made here, it is not difficult to propose the use of a median estimate derived from multiple bioassays. However, the optimmn procedure to foUow when there are bioassays available in two or more rodent species is not clear. Allometric scaling is ruled out by the obsawations, but estimation of a better (perhaps entirely empirical) replacement would substantially benefit from an updated examination of epidemiological data and incorporation of corresponding more recent, standardized, rodent bioassays. Extrapolation of intraspecies variability directly between species pairs appears impossible but that does not rule out the possibility of a relationship between species triples, nor the possibility of correlations with other endpoints. Even if no such extrapolation procedme can be devised, it is nevertheless possible to devise a probabilistic extrapolation that takes account of the lack of correlation. 

In a later study. Swanson and coworkers [81] studied the cure of acetylene-terminated poly(imide)s selectively labelled at various positions with nuclei. Curing of the sample, labelled at the imide carbonyl group, confirmed the completion of the imidization reaction on heating. The product of addition onto the carboxyl group was not observed. Four new peaks were identified in the spectrum of the cured sample labelled at the Ci-acetylene group, while a similar result was obtained for the sample labelled at the C2-acetylene position. Analysis of these results rules out the participation of coupling reactions and the biradical mechanism, which would produce triple-bond structures, but confirms the presence of the product of cyclotrimerization and Friedel-Crafts reactions. The latter mechanism is confirmed from the presence of small peaks due to aliphatic carbons in the spectra of the materials labelled at the acetylene groups. 

Stereospecific synthesis of arylidene and allylidene cyclopentanes and cyclohexanes can be achieved by palladium-catalyzed cyclization of carbanions containing a C — C triple bond in the presence of aryl or vinyl halides52 33". The reaction is stereoselective, occurring with irans selectivity. Thus, a palladacyclic intermediate, resulting from initial aryl or vinyl carbapallada-tion, is ruled out in favor of primary carbanion addition to the alkyne unit. 

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