To use meta-analysis to determine the diagnostic accuracy of contrast agent-enhanced multidetector computed tomography (CT) in primary acute mesenteric ischemia (AMI).
The PubMed search engine and ...five other electronic databases were searched for "mesenteric ischemia," "computed tomography," and related terms in articles published between January 1996 and September 2009, without language restrictions. Reference lists of retrieved articles were also searched. Two reviewers independently selected six studies that reported 2 x 2 contingency data on the diagnostic accuracy of multidetector CT in primary AMI in at least 10 patients with disease and 10 patients without disease and that used surgery or clinical outcome as the reference standard. Study data were independently extracted by the two reviewers, and disagreement was resolved by consensus. The study quality was assessed by using items from the Quality Assessment of Diagnostic Accuracy Studies tool. The primary 2 x 2 count data were investigated with a bivariate random-effects meta-analysis of sensitivity and specificity.
Three studies were prospective, and three were retrospective. All studies were of high quality. The CT scanners used in the included studies had between four and 40 rows. The between-study heterogeneity was low to moderate. Overall, AMI was found in 142 of 619 studied cases. The meta-analysis showed a pooled sensitivity of 93.3% (95% confidence interval: 82.8%, 97.6%) and a pooled specificity of 95.9% (95% confidence interval: 91.2%, 98.2%).
On the basis of a thorough clinical examination, contrast-enhanced multidetector CT allows the diagnosis of primary AMI with high sensitivity and specificity. Thus, it may be used as the first-line imaging method.
Pandapower is a Python-based BSD-licensed power system analysis tool aimed at automation of static and quasi-static analysis and optimization of balanced power systems. It provides power flow, ...optimal power flow, state estimation, topological graph searches, and short-circuit calculations according to IEC 60909. pandapower includes a Newton-Raphson power flow solver formerly based on pypower , which has been accelerated with just-in-time compilation. Additional enhancements to the solver include the capability to model constant current loads, grids with multiple reference nodes, and a connectivity check. The pandapower network model is based on electric elements, such as lines, two- and three-winding transformers, or ideal switches. All elements can be defined with nameplate parameters and are internally processed with equivalent circuit models, which have been validated against industry standard software tools. The tabular data structure used to define networks is based on the Python library pandas, which allows comfortable handling of input and output parameters. The implementation in Python makes pandapower easy to use and allows comfortable extension with third-party libraries. pandapower has been successfully applied in several grid studies as well as for educational purposes. A comprehensive publicly available case study demonstrates a possible application of pandapower in an automated time-series calculation.
•Voltage magnitude and line loading monitoring scheme using artificial neural networks.•Low estimation errors even with distributed generation and different switching states.•The presented ...hyperparameters are transferable for use in other grids.
The increasing number of distributed generators connected to distribution grids requires a reliable monitoring of distribution grids. Economic considerations prevent a full observation of distribution grids with direct measurements. First approaches using a limited number of measurements to monitor distribution grids exist, some of which use artificial neural networks (ANN). The current ANN-based approaches, however, are limited to static topologies, only estimate voltage magnitudes, do not work properly when confronted with a high amount of distributed generation and often yield inaccurate results. These strong limitations have prevented a true applicability of ANN for distribution system monitoring. The objective of this paper is to overcome the limitations of existing approaches. We do that by presenting an ANN-based scheme, which advances the state-of-the-art in several ways: Our scheme can cope with a very low number of measurements, far less than is traditionally required by the state-of-the-art weighted least squares state estimation (WLS SE). It can estimate both voltage magnitudes and line loadings with high precision and includes different switching states as inputs. Our contribution consists of a method to generate useful training data by using a scenario generator and a number of hyperparameters that define the ANN architecture. Both can be used for different power grids even with a high amount of distributed generation. Simulations are performed with an elaborate evaluation approach on a real distribution grid and a CIGRE benchmark grid both with a high amount of distributed generation from photovoltaics and wind energy converters. They demonstrate that the proposed ANN scheme clearly outperforms state-of-the-art ANN schemes and WLS SE under normal operating conditions and different situations such as gross measurement errors when comparing voltage magnitude and line magnitude estimation errors.
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The emergent properties resulting from selective supramolecular interactions are of significant importance for materials and chemical systems. For the directed use of such properties, a fundamental ...understanding of the interaction mechanism and the resulting mode of function is necessary for a tailored design. The self‐induced diastereomeric anisochronism effect (SIDA), which occurs in the intermolecular interaction of chiral molecules, generates unique properties such as chiral self‐recognition and nonlinear effects. Here we show that anisidine amino acid diamides lead to extraordinary signal splitting in NMR spectra through supramolecular interaction and homochiral self‐recognition. By systematic experiments we have investigated the underlying SIDA effect, explored its limits and finally successfully utilized it in the determination of enantiomeric ratios by NMR spectroscopy of chiral ‘SIDA‐inactive’ compounds such as thalidomide.
Self‐recognition of enantiomers: Anisidine amino acid diamides show extraordinary signal splitting in NMR spectra through supramolecular interaction and homochiral self‐recognition making them to versatile NMR shift‐reagents.
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Novel l‐tartaric acid based stereodynamic biphenylbisphosphinite ligands with anilino linkers were prepared as cyclic diamide compounds. The influence of the constitutional substitution pattern of ...the amino group at the aniline moiety on the diastereoselective formation of the ligand was investigated. While the meta‐anilino bridged ligands showed a highly dynamic behavior and no discrimination between (Rax) and (Sax) configuration, l‐tartaric acid substitution on ortho‐anilino bridged ligands leads to diastereoselective self‐alignment of the central biphenol axis, which controls the stereoselectivity of the ligand and catalyst. The experimental findings were corroborated by theoretical calculations. In the rhodium‐catalyzed enantioselective hydrogenation of methyl 2‐acetamidoacrylate (MAA), an enantiomeric ratio of 75 : 25 (R/S) was obtained for the ortho‐substituted ligand.
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For the preparation of chiral drugs, both stereochemically stable and flexible catalysts in combination with chiral auxiliaries can be used. Here, chiral induction plays an important role in ...generating an enantiomerically pure catalyst. We demonstrate a successful approach to the spontaneous deracemization of tropos ligands for asymmetric catalysis. Three different constitutional isomers of a bisphosphinite ligand decorated with l-valine moieties (interaction units) linked to the flexible biphenyl system by a phenylene bridge for inducing a chiral switch were prepared. The substitution pattern’s influence on the attached intermolecular recognition sites was systematically investigated. We can show that biomimetic intramolecular hydrogen bonding leads to a pronounced diastereoselective enrichment of one of the ligand stereoisomers. As a result, in the asymmetric Rh-catalyzed hydrogenation of prochiral olefins using these ligands, enantiomeric ratios of up to 95.8:4.2 (S) were obtained. Of particular note is the inversion of enantioselectivity relative to the previously reported BIBIPHOS-Rh catalyst due to the altered orientation of the biphenyl moiety from (R ax) to (S ax). The enantioselectivities achieved by appropriate intramolecular interlocking are remarkable for a tropos ligand/catalyst. The strategy presented here represents a powerful approach for the spontaneous alignment of tropos ligands, yielding high enantioselectivities in asymmetric catalysis.
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Contrast-enhanced magnetic resonance angiography (MRA) is a noninvasive, radiation-free imaging method for studying peripheral arterial disease (PAD) of the lower extremities.
To summarize evidence ...of prospective studies about how well MRA identifies or excludes arterial steno-occlusions (50% to 100% lumen reduction) in adults with PAD symptoms.
PubMed and 3 other databases were searched from 1998 to 2009 without language restrictions.
Two independent reviewers selected 32 studies that compared MRA with intra-arterial digital subtraction angiography in PAD. Eligible studies were prospective and provided data to reconstruct 2 x 2 or 3 x 3 contingency tables (<50% stenosis vs. > or =50% stenosis or occlusion of arterial segments) in at least 10 patients with PAD symptoms.
Two reviewers independently assessed the study quality and extracted the study data, with disagreements resolved by consensus.
The 32 included studies generally had high methodological quality. About 26% of the 1022 included patients had critical limb ischemia with pain at rest or tissue loss. Overall, the pooled sensitivity of MRA was 94.7% (95% CI, 92.1% to 96.4%) and the specificity was 95.6% (CI, 94.0% to 96.8%) for diagnosing segmental steno-occlusions. The pooled positive and negative likelihood ratios were 21.56 (CI, 15.70 to 29.69) and 0.056 (CI, 0.037 to 0.083), respectively. Magnetic resonance angiography correctly classified 95.3%, overstaged 3.1%, and understaged 1.6% of arterial segments.
Similar to most studies of computed tomographic angiography in PAD, the primary studies reported the diagnostic accuracy of MRA on a per-segment basis, not a per-patient basis.
This meta-analysis of 32 prospective studies further increases the evidence that contrast-enhanced MRA has high accuracy for identifying or excluding clinically relevant arterial steno-occlusions in adults with PAD symptoms.
None.
To investigate prospectively which of several body size parameters are suitable for individual dose adaptation in body computed tomography (CT) of adults.
Three body regions (thorax, abdomen, pelvis) ...were scanned exclusively for clinical reasons, with institutional ethical approval and informed consent. For each of the three regions, 50 men and 50 women (aged 18-87 years) were studied (300 scans total). Individual x-ray properties for each scan were summarized with a water-equivalent diameter (Dw). Different body size parameters, based on weight, height, and shape, were correlated with Dw by using regression analysis. This resulted in Dw estimation errors of different magnitudes, indicated with 95% prediction intervals. The errors from weight were compared with those from each of the other body parameters by using comparison of variance in paired samples (P < .05). In addition, a topogram-based estimate for Dw was studied, which simulated an automated body size measurement.
For the thorax, abdomen, and pelvis, mean Dw was 28.0, 29.1, and 29.3 cm, and estimation of Dw from weight enabled 95% prediction intervals of +/-2.5, +/-2.4, and +/-2.6 cm, respectively. Combinations of height and weight were only slightly more or even less exact than were measurements from only weight. Diameter-related parameters such as body circumference were similar to or better than weight. However, the topogram-based estimate was significantly more exact.
Body weight and circumference enable suitable estimates for individual dose adaptation in body CT of adults if automated dose adaptation is not available.
Objective
Cerebral aneurysms can cause substantial morbidity and mortality, specifically if they rupture, leading to nontraumatic subarachnoid hemorrhage (SAH). This meta‐analysis summarizes evidence ...about the accuracy of noninvasive computed tomographic (CT) angiography for diagnosing intracranial aneurysms in symptomatic patients.
Methods
Four databases including PubMed were searched without language restrictions from January 1995 to February 2010. Two independent reviewers selected and extracted 45 studies that compared CT angiography with digital subtraction angiography (DSA) and/or intraoperative findings in patients suspected of having cerebral aneurysms. Data from eligible studies were used to reconstruct 2 × 2 contingency tables on a per‐patient basis in at least 5 diseased and 5 nondiseased patients, with additional data on a per‐aneurysm basis when available.
Results
The 45 included studies generally were of high methodological quality. Among the 3,643 patients included, about 86% had nontraumatic SAH, and 77% had cerebral aneurysms. Overall, CT angiography had a pooled sensitivity of 97.2% (95% confidence interval, 95.8–98.2%) for detecting and specificity of 97.9% (95.7–99.0%) for ruling out cerebral aneurysms on a per‐patient basis. On a per‐aneurysm basis, the pooled sensitivity was 95.0% (93.2–96.4%), and the specificity 96.2% (92.9–98.0%). The diagnostic accuracy of CT angiography with 16‐ or 64‐row multidetector CT was significantly higher than that of single‐detector CT, especially in detecting small aneurysms of ≤4mm in diameter.
Interpretation
CT angiography has a high accuracy in diagnosing cerebral aneurysms, specifically when using modern multidetector CT. In the future, CT angiography may increasingly supplement or selectively replace DSA in patients suspected of having a cerebral aneurysm. ANN NEUROL 2011
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Background In coronary computed tomography (CT) angiography (CTA) prospective electrocardiography triggering requires less radiation dose than retrospective electrocardiography gating but provides ...less cardiac phases for interpretation. This meta-analysis presents a concise and comprehensive head-to-head comparison of image quality, diagnostic accuracy, and radiation dose of prospectively triggered coronary CTA vs retrospectively gated CTA in patients with suspected or known coronary artery disease (CAD). Methods In patients with CAD and without tachyarrhythmia, eligible studies (selected from 4 databases) compared prospectively triggered vs retrospectively gated CTA (performed with ≥64-slice CT or dual-source CT) in 2 groups having approximately similar patient characteristics, scored CTA image quality, and/or assessed how accurately CTA diagnoses ≥50% coronary stenoses compared with catheter angiography and reported the radiation dose. The data were meta-analyzed by random-effects models, with CIs provided in the text. Results Among 3,330 patients from 20 included studies, 91.3% of CTAs (segments: 97.8%) had diagnostic quality with prospective triggering and 93.3% of CTAs (segments: 98.4%) with retrospective gating ( P > .05). Among 664 patients from 5 studies, the pooled sensitivity/specificity of diagnostic CTAs was 98.7%/91.3% (segment level: 91.3%/97.7%) with prospective triggering and 96.9%/95.8% (segment level: 93.1%/97.6%) with retrospective gating ( P > .05). The pooled effective dose was 3.5 mSv with prospective triggering and thus, by a factor of 3.5, lower than the pooled effective dose of retrospective gating, which was 12.3 mSv ( P < .01). Conclusions In patients with CAD and without tachyarrhythmia, prospectively triggered coronary CTA provides image quality and diagnostic accuracy comparable with retrospectively gated CTA, but at a much lower radiation dose.
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