1,720,973 research outputs found
Automatic postprocessing for the assessment of quantitative human myocardial perfusion using MRI
No full textComparison of 3 Contrast Agents and Recommendation of Feasible Doses
No full textObjective The aims of this study were to compare 3 contrast agents and to define feasible doses for quantitative lung perfusion imaging using the dual-bolus approach in dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI). Materials and Methods Ten healthy volunteers (6 males, 4 females; mean age, 23.5 years) underwent DCE-MRI at 1.5 T using a 3D FLASH sequence. After a prebolus, 3 doses of gadopentetate dimeglumine (Gd-DTPA), gadofosveset, and gadobenate dimeglumine (Gd-BOPTA) were evaluated. Dose regimes were as follows: Gd-DTPA: 3.0 mL, 6.0 mL, and 12.0 mL with 1.5 mL prebolus; gadofosveset: 1.5 mL, 3.0 mL, and 6.0 mL with 0.8 mL prebolus; and Gd-BOPTA: 1.5 mL, 3.0 mL, and 6.0 mL with 0.8 mL prebolus. Pulmonary blood flow (PBF), pulmonary distribution volume, and mean transit time were assessed for each bolus. Region of interest measurements were used to determine the arterial input function (AIF) in the pulmonary trunk and signal intensities in lung parenchyma. Two radiologists independently rated the subjective image quality of the quantitative perfusion maps based on a 4-point Likert scale. Results Dose-dependent signal saturation effects were observed for all 3 contrast agents concerning AIF and parenchyma measurements. Signal yields were comparable using Gd-BOPTA (AIF, 214.49 arbitrary units [AU]; parenchyma, 41.7 AU) and Gd-DTPA (207.43 AU; 36.3 AU). Gadofosveset showed significantly lower signal yield (165.74 AU; 25.2 AU; p < 0.008). Highest signal increase was observed for Gd-DTPA. Using Gd-DTPA, mean PBF values for the 3 doses (3 mL, 6 mL, 12 mL) in mL/min per milliliter lung volume were 2.9 +/- 1.5, 2.4 +/- 1.1, and 1.6 +/- 1.0. For the 3 doses of gadofosveset (1.5 mL, 3 mL, 6 mL) mean PBF results were 3.1 +/- 1.1, 1.9 +/- 0.7, and 1.2 +/- 0.6. Last, mean PBF values for Gd-BOPTA (1.5 mL, 3 mL, 6 mL) were 3.4 +/- 1.7, 2.8 +/- 1.3, and 2.0 +/- 0.8. Measurements provided consistent values for all perfusion parameters (PBF, pulmonary distribution volume, mean transit time) when compared with reference literature. Contrast dose volume and the applied contrast agent had no relevant effects on the image quality scores. Conclusions The dual-bolus approach using a 3D FLASH sequence is a feasible tool for quantitative lung perfusion imaging. Small boluses of 3 mL for Gd-DTPA, 1.5 mL for Gd-BOPTA, and 1.5 mL for gadofosveset provide sufficient signal yield for quantitative parenchyma measurements. Using higher boluses falsely lower perfusion values have to be considered due to signal saturation effects. Although gadofosveset yielded the lowest signal, the generated quantitative perfusion maps were of diagnostic quality
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
A model‐based reconstruction technique for quantitative myocardial perfusion imaging
No full textPurpose: To reduce saturation effects in the arterial input function (AIF) estimation of quantitative myocardial first-pass saturation recovery perfusion imaging by employing a model-based reconstruction. Theory and Methods: Imaging was performed with a saturation recovery prepared radial FLASH sequence. A model-based reconstruction was applied for reconstruction. By exploiting prior knowledge about the relaxation process, an image series with different saturation recovery times was reconstructed. By evaluating images with an effective saturation time of approximately 3 ms, saturation effects in the AIF determination were reduced. In a volunteer study, this approach was compared with a standard prebolus technique. Results: In comparison to the low-dose injection of a prebolus acquisition, saturation effects were further reduced in the AIFs determined using the model-based approach. These effects, which were clearly visible for all six volunteers, were reflected in a statistically significant difference of up to 20% in the absolute perfusion values. Conclusion: The application of model-based reconstruction algorithms in quantitative myocardial perfusion imaging promises a significant improvement of the AIF determination. In addition to greatly reducing saturation effects that occur even for the prebolus methods, only a single bolus has to be applied. (C) 2015 Wiley Periodicals, Inc.Graduate School of Life Sciences, University of Wurzbur
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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