1,721,222 research outputs found
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
Image Quality and Radiation Exposure with a Low Tube Voltage Protocol for Coronary CT Angiography
No full textZiel der Arbeit war es, den Einfluss eines Niedrigdosisprotokolls mit verringerter Röhrenspannung auf die Bildqualität und Strahlendosis zu untersuchen. In die Studie wurden 400 nicht übergewichtige Patienten mit Indikation zur CT-Angiographie eingeschlossen, die per Zufallsverfahren in zwei Gruppen eingeteilt wurden. Eine Gruppe wurde mit dem Standartprotokoll mit 120kV untersucht, während die andere Gruppe einer CT-Untersuchung mit 100kV unterzogen wurde. Die Bildqualität wurde anschließend anhand einer 4 Punkte-Skala von zwei unabhängigen Untersuchern bewertet. Die Ergebnisse zeigten, dass in der 100kV-Gruppe eine Reduktion der effektiven Strahlendosis um 31% gelang, während der Bildqualitätsscore in beiden Gruppen gleich blieb. Somit kann die Schlussfolgerung gezogen werden, dass das 100kV-Protokoll für die Untersuchung von nicht-übergewichtigen Patienten geeignet ist.Background:
Coronary CT Angiography has emerged as a useful diagnostic imaging modality for non-invasive assessment of coronary artery disease in patients with low to intermediate risk profile. But concerns have been raised about radiation exposure during coronary CTA. The use of a 100 kVp tube voltage scan protocol effectively lowers coronary CTA radiation dose. Recent studies have demonstrated an infrequent use of this dose-reduction strategy in daily practice which is most likely explained by a lack of scientific data demonstrating maintained image quality.
Objectives:
The purpose of this study was to evaluate image quality and radiation dose using a 100 kVp tube voltage scan protocol compared with standard 120 kVp for coronary computed tomography angiography
Methods:
400 non-obese patients undergoing clinically indicated coronary CTA for suspected artery disease were enrolled in 8 institutions. 202 patients were randomly assigned to a 100 kV protocol and 198 patients to a 120 kV protocol. The primary end point was to demonstrate non-inferiority in image quality with the 100 kV protocol, which was assessed by a 4-point grading score. Secondary end points included radiation dose and need for additional diagnostic tests during follow-up.
Two independent observers assigned a score from 1 to 4 to each coronary artery as follows: score 4 for excellent image quality, score 3 for good image quality despite presence of smaller artifacts, score 2 for sufficient image quality but considerable artefacts and score 1 for non-diagnostic image quality. For the non-inferiority analysis, a margin of -0.2 image quality score points for the difference between both scan protocols was pre-defined. Effective dose was determined based on the dose-length product. Furthermore, the need for subsequent cardiac tests was assessed by a telephone-interview with every patient after 30 days.
Results:
The 100 kV protocol was associated with a 31% relative reduction in radiation exposure (dose-length product: 868 ± 317 mGy x cm with 120 kV vs. 599 ± 255 mGy x cm with 100 kVp; p = 0.0001). The mean image quality scores in the two groups did not differ (100 kV- Group: 3.30 ±0.67; 120kV-Group 3.28 ± 0.68; p = 0.742).Image quality of the 100 kVp protocol was not inferior, as demonstrated by the 97.5% confidence interval of the difference, which did not cross the pre-defined noninferiority margin of -0.2. At 30-day follow-up, the need for additional diagnostic studies did not differ (13.4% vs. 19.2% for 100 kV vs. 120 kV, respectively; p = 0.114).
Conclusions
A coronary CTA protocol using 100 kV tube voltage in non-obese patients maintained image quality, but reduced radiation exposure by 31% as compared with the standard 120 kVp protocol. Thus, 100 kVp scan protocols should be considered for nonobese patients to keep radiation exposure as low as reasonably achievable
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
Radiation dose estimates of coronary dual source CT angiography in comparison to 64-slice CT
No full textDie Strahlendosis der koronaren CT-Angiographie für das Dual Source CT (DSCT) wurde mit dem 64-Zeilen MSCT (64-MSCT) verglichen und der Einfluss verschiedener Untersuchungsprotokolle an 2822 Patienten untersucht.
In der klinischen Routine ergab sich am DSCT gegenüber dem 64-MSCT ein um ca. 25% reduziertes Dosis-Längen-Produkt (DLP). Beim Vergleich eines korrspondierenden Untersuchungsprotokolls mit 120 kV lag das DLP am DSCT ca. 25% höher als am 64-MSCT. Durch Verwendung dosissparender Algorithmen konnte am DSCT eine Dosisreduktion um bis zu 80% gegenüber dem 64-MSCT erreicht werden.We analyzed radiation dose for 64-slice CT and dual source CT (DSCT) coronary angiography and the effect of algorithms for dose reduction in 2822 patients. The average dose length product (DLP) for DSCT in clinical routine was shown to be 25% lower than for 64-slice CT. When using a comparable scan protocol of 120 kV for 64-slice CT and DSCT, respectively, DSCT coronary angiography had a 25% higher DLP. The use of ECG-dependent tube current modulation, 100 kV tube voltage and a sequential scan protocol resulted in a radiation dose reduction up to 80% for DSCT coronary angiography
Cardiovascular risk assessment based on the extent of coronary calcium in contrast-enhanced coronary CT angiography
No full textAus zwei Kohorten von insgesamt 600 Patienten wurde eine Methode entwickelt und validiert, die koronare Kalklast als kardiovaskulären Risikofaktor aus Aufnahmen der kontrastierten kardialen computertomographischen Angiographie (CCTA) zu ermitteln und nicht, wie herkömmlich, aus nativen computertomographischen (CT) Aufnahmen. Die durch die CCTA ermittelten Kalkscores zeigten eine hohe Korrelation (r=0,954; p<0.001) zu den Scores aus nativen Aufnahmen.In a two-cohort study of 600 patients a method was developed and validated to assess the extent of coronary calcification and the associated cardiovascular risk category in cardiac computed tomography angiography (CCTA). The results of coronary artery calcium scoring in the non-enhanced scan and CCTA scan showed a high correlation (r=0.954; p<0.001)
Impact of non-invasive coronary CT angiography in pilots and flight safety personnel of the German Armed Forces with suspected coronary heart disease
No full textDas Ziel der vorliegenden Arbeit war es, die nicht invasive koronare CT Angiographie bezüglich ihrer Bedeutung in der flugmedizinischen Diagnostik bei Piloten und flugsicherheitsrelevantem Personal der Bundeswehr mit Verdacht auf eine koronare Herzerkrankung (KHK) zu evaluieren. Bei insgesamt 110 untersuchten Patienten konnte eine stenosierende KHK bei 78 (71%) Patienten mittels CT Angiographie ausgeschlossen werden. Der klinische Verlauf dieser Patienten gestaltete sich über 19 ±11 Monate bei allen bis auf einen Patienten unauffällig. Dieser Patient erlitt bei nachgewiesener nicht-stenosierender Koronaratherosklerose einen Myokardinfarkt. Bei 32/110 Patienten ergab sich computertomographisch der Verdacht auf eine KHK, der bei 19 Patienten durch eine invasive Herzkatheteruntersuchung bestätigt wurde; 8 Patienten wurden operativ oder interventionell revaskularisiert. Zusammenfassend stellt die koronare CT Angiographie eine sehr genaue und wichtige diagnostische Methode in der flugmedizinischen Diagnostik bei Piloten und flugsicherheitsrelevantem Personal dar.The purpose of the current study was to evaluate the impact of non-invasive coronary CT angiography in pilots and flight safety personnel of the German Armed Forces with suspected coronary heart disease (CHD). Coronary CT angiography allowed for excluding obstructive CHD in 78 of 110 (71%) included patients. Clinical follow-up, over a mean of 19 ±11 months, was uneventful in all but one patient. This patient with proven non-obstructive coronary atherosclerosis by CT, suffered from a myocardial infarction. Obstructive CHD was suspected by coronary CT angiography in 32 of 110 patients; invasive coronary angiography was performed in 19 of these patients, which confirmed the presence of obstructive CHD in all patients and 8 of these patients did undergo operative or percutaneous coronary revascularization. In summary, coronary CT angiography appears to be a very accurate and important diagnostic tool to assess CHD in aero-medicine
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