1,720,973 research outputs found
Estimation of 511 keV gamma scatter fraction in WLS layer in total-body J-PET : a simulation study
Get PDFPositron emission tomography (PET) is essential in medical diagnostics and monitoring therapy. The J-PET Collaboration at Jagiellonian University is developing a new generation of Total-Body PET scanners based on plastic scintillators. One of the Total-Body J-PET designs comprises seven rings, each consisting of 24 modules. A single module is built of 2 layers, each comprises of 16 axially arranged plastic scintillator strips of 330 mm length, read out by silicon photomultiplier (SiPM) arrays from both ends, and an additional layer of 50 wavelength shifter (WLS) bars, placed perpendicular to plastic layers. This study estimates the scatter fraction of the Total-Body J-PET manufactured from plastic scintillator strips according to the NEMA NU 2-2018 standards by using the GATE software. The scatter phantom was simulated as a solid cylinder with a length of 700 mm and an outside diameter equal to 203 mm. At the same time, at a radial distance of 45 mm, we have a hole with a diameter of 6.4 mm where a linear source with total activity of 1 MBq is placed. For data processing, sinograms were generated, and the Single Slice Rebinning (SSRB) algorithm was used for the scatter fraction calculation. As a result, we estimate that addition of the WLS layer is increasing the scatter fraction by 0.67%
Optimization of the WLS design for positron emission mammography and Total-Body J-PET systems
Get PDFTotal body positron emission tomography (PET) instruments are medical imaging devices that detect and visualize metabolic activity in the entire body. The PET scanner has a ring-shaped detector that surrounds the patient, which detects the gamma rays emitted by the tracer as it decays. Usually, these detectors are made up of scintillation crystals coupled to photodetectors that convert the light produced by the scintillation crystal into electrical signals. The Jagiellonian Positron Emission Mammograph (J-PEM) is the first J-PET prototype module based on a novel idea with a plastic scintillator and wavelength shifter (WLS). At the same time, it is a prototype module for the total-body J-PET system. J-PEM can be an effective system for the detection and diagnosis of breast cancer in its early stage by improving sensitivity. This can be achieved using superior timing properties of plastic scintillators and combined with the WLS sheets readout. In this paper, we present an application of the Geant4 program for simulating optical photon transport in the J-PEM module. We aim to study the light transport within scintillator bars and WLS sheets to optimize gamma-ray hit position resolution. We simulated a pencil beam of 511 keV photons impinging the scintillator bar at different locations. For each condition, we calculated the value of the pulse height centroid and the spread of the photon distribution. Some free parameters of the simulation, like the reflectivity and the effective attenuation length in the sheet, were determined from a comparison to experimental data. Finally, we estimate the influence of the application of WLS layer in the total-body J-PET on the scatter fraction. To optimize the performance of the J-PEM module, we compared geometry with the number of WLS strips 50 and 83. It was found, that spatial resolution was 2.7 mm and 3.5 mm FWHM for 50 and 83 WLS strips respectively. Despite the better granularity, the 83-strip WLS geometry exhibits poorer resolution due to fewer photons being transmitted to the strip, resulting in large fluctuations of signal
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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