1,721,058 research outputs found
Imaging performance of silicon photomultipliers coupled to BGO and CsI:Na arrays
No full textThe aim of this study is to investigate the imaging performance of a silicon photomultiplier array (ArraySL-4) photodetector for possible PET and potentially SPECT applications using BGO and CsI(Na) pixellated scintillators. Our main objectives are: i) the comparison of the ArraySL-4 to the older version SensL's SPMArray4 photo detector in terms of energy resolution and peak to valley ratio of a row profile in the flood image and ii) the study of the effect of different coupling schemes using ultra transmitting glass windows of various thicknesses. We acquired raw images from two pixellated scintillators (BGO with 2 × 2×5 mm3 and CsI:Na with 1 × 1×5 mm3 pixel sizes) irradiated with 511 keV and 1274.5 keV γ-rays from a 22Na source. The SiPM array detector allowed the clear visualization of the discrete 2 × 2 mm2 pixellated BGO and 1 × 1 mm2 CsI:Na scintillator elements at room temperature (no cooling). The energy resolution of the new SensL ArraySL-4 detector for the 2 × 2×5 mm3 BGO pixellated scintillator array is improved for rather 6 percentage points (energy resolution improvement equal to 22%) and the peak to valley ratio is measured higher for both scintillator arrays (for BGO 68% (1.7 × ) and for CsI:Na 154% (2.5 × )) compared with SPMArray4. The clear identification of the 1 × 1 mm2 CsI:Na scintillator elements provides evidence that the combination of those SiPMs with even smaller arrays can be used as an efficient imaging detector module. Optical coupling significantly improves image uniformity, while the use of BK7 ultra transmitting glass window with 1.35 mm thickness provided the best measure energy resolution equal to 21.5%
New opportunities in the design of gamma-camera collimators for medical imaging
No full textIn nuclear medicine, the gamma camera is one of the more used imaging devices for radionuclide imaging. Gamma camera provide an image of the target organ, with high spatial resolution and sensitivity; gamma cameras use collimators. This paper presents a simple and customizable collimator to be used in radionuclide imaging for preclinical studies, using additive manufacturing (AM) techniques. A numerical analysis, based on GATE Monte Carlo toolkit (vGate 8.2), has been conducted to simulate different configurations of an already working collimator used as reference. In addition to the standard collimator geometry with alternatives materials, we also propose a new concept of collimator to be easily 3D printed, using different 3D printing technologies. We have simulated collimators with square apertures of 1.5 mm and septa of 0.4 mm of thickness, source was Tc99m. The materials simulated were standard tungsten, a PLA doped with tungsten (Rapid 3DShield Tungsten Filament – Virtual Foundry), a classical PLA filament and PA2200 for the new concept. The results show a similar behavior for what concern the spatial resolution, while for the sensitivity a reduction of about 45% of entries is reported. This is due mainly since the extruded pixel, made of PLA or PA2200, have higher density (≈ 1.24 g/cm^3 for PLA and ≈ 0,95 g/cm^3 for PA2200) with respect to air (≈ 0,0012 g/cm^3). Further studies are necessary to explore optimization of the used design to reduce the impact of material density
Small field of view nuclear imaging detector evaluation using Tc-99m and Ga-67 radioisotopes
No full textIn this work we report the imaging performance of a small field of view planar scintigraphic system for low and medium energy radiotracers imaging. 99mTc (140 keV) and 67Ga (93 keV (P1, 42%), 184 keV (P2, 21%), 300 keV (P3, 17%), 393 keV (P4, 5%)) radioisotopes were used to evaluate the nuclear imaging detector in terms of non-uniformity, energy resolution, system spatial resolution and system sensitivity. Moreover, detector's ability to reliably quantify activity variations in the useful field of view has been evaluated. Specific collimator for given photon energy range is needed, in order to reduce image degradation due to photon scattering and penetration. Three parallel hole collimators different in geometry were studied. Results show that all of them are suitable for 99mTc and 67Ga molecular imaging applications, given that only the first photopeak in the case of 67Ga has to be used for imaging. In this case, accurate quantitative information is obtained with all 3 collimators for both radioisotopes. For 99mTc the most appropriate collimator is the one with the thinner septa walls and the lower height, while for 67Ga the thickest septa and higher height collimator. Dual isotope imaging is applicable using appropriate energy windows and appropriate collimator depending on the application
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
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
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