1,721,030 research outputs found
Optical imaging of irradiated cyclotron target window foils using Cerenkov and radioluminescence imaging
No full textRadioisotopes production for PET radiopharmaceuticals is performed using cyclotrons resulting in radio activation of different cyclotron components. It is thus necessary to measure the level of radiation exposure and, if possible, to image the areas where most of the radiations are emitted in particular during maintenance or decommissioning procedures. In this work we present a novel optical imaging approach using Cerenkov luminescence imaging (CLI) and radioluminescence imaging (RLI). CLI was performed by placing a glass Cerenkov radiator on a target window (Havar foils) and RLI data were obtained by covering the Havar foils with an intensifying screen. CLI or RLI were acquired using a small animal optical imaging system used in bioluminescence mode without the use of any optical filters. The analysis of the normalized radiance line profiles of both CLI and RLI images showed a similar pattern, however the absolute radiance of the RLI signal is several order of magnitude higher with respect to CLI. We conclude that optical imaging with CLI and RLI can be considered a novel method to detect and image activation areas in irradiated samples from a medical cyclotron
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
State of art and optimization perspectives for breast imaging
No full textBreast screening with mammography is the most effective method of detecting early-stage breast cancer and reducing related mortality. Among the intrinsic limits of mammography, in terms of clinical performance, the overlapping of normal and pathological tissues is one of the most influential. Some new techniques as Digital Breast Tomosynthesis (DBT) is expected to overcome this limitation by providing a quasi-three-dimensional (3D) image that could lead to improve the accuracy of mammography. Another way to increase accuracy and sensitivity is represented by a double exposure of the patient before and after intravenous injection of contrast media, this technique is called Contrast-enhanced digital (or spectral) mammography (CEDM, CESM). Furthermore, highly specialized software has been developed which is able to detect suspicious mammographic findings. This technology is very interesting especially in the screening field, in fact there are multiple ongoing studies evaluating the use of Artificial Intelligence (AI) as a second reader. To date, screening mammography is the only imaging modality that has proven to significantly lower breast cancer mortality. Tomosynthesis demonstrated excellent sensitivity and specificity but the technique did not meet the expectations given the risk of over diagnosis as well as the lack of reduction in the number of interval breast cancer. CESM could in some cases serve as an alternative imaging tool to MRI. AI, seems to be competing with the breast radiologist and its use as a second reader in breast screening programs is already being proposed
Set-up error in supine-positioned patients immobilized with two different modalities during conformal radiotherapy of prostate cancer
No full textBackground: Conformal radiotherapy requires reduced margins around the clinical target volume (CTV) with respect to traditional radiotherapy techniques. Therefore, high set-up accuracy and reproducibility are mandatory. Purpose: To investigate the effectiveness of two different immobilization techniques during conformal radiotherapy of prostate cancer with small fields. Materials and methods: 52 patients with prostate cancer were treated by conformal three- or four-held techniques with radical or adjuvant intent between November 1996 and March 1998. In total, 539 portal images were collected on a weekly basis for at least the first 4 weeks of the treatment on lateral and anterior Is MV X-ray fields. The average number of sessions monitored per patient was 5.7 (range 4-10). All patients were immobilized with an alpha-cradle system; 25 of them were immobilized at the pelvis level (group A) and the remaining 27 patients were immobilized in the legs (group B). The shifts with respect to the simulation condition were assessed by measuring the distances between the same bony landmarks and the held edges. The global distributions of cranio-caudal (CC), posterior-anterior (PA) and left-right (LR) shifts were considered; for each patient random and systematic error components were assessed by following the procedure suggested by Bijhold et al. (Bijhold J, Lebesque JV, Hart AAM, Vijlbrief RE. Maximising set-up accuracy using portal images as applied to a conformal boost technique for prostatic cancer. Radiother. Oncol. 1992;24:261-271). For each patient the average isocentre (3D) shift was assessed as the quadratic sum of the average shifts in the three directions. Results: Group B showed a better accuracy and reproducibility than group A for PA shifts (2.6 versus 4.4 mm, 1 SD), LR shifts (2.4 versus 3.6 mm, 1 SD) and CC shifts (2.7 versus 3.3 mm, 1 SD). Furthermore, group B showed a rate of large PA shifts (>5 mm) equal to 4.4% with respect to the 21.6% of group A (P < 0.0001). This value was also better than the corresponding value found in a previously investigated group of 21 non-immobilized patients (Italia C, Fiorino C, Ciocca M, et al. Quality control by portal film analysis of the conformal radiotherapy of prostate cancer: comparison between two different institutions and treatment techniques (abstract). Radiother. Oncol. 1997;43(Suppl. 2):S16, 16.8%, P = 0.001). For both groups there was no clear prevalence of one component (systematic or random) with respect to the other. The average isocentre shifts (averaged on all patients) were 3.0 mm (+/-1.4 mm, I SD) for group B and 5.0 mm (+/-2.8 mm, 1 SD) for group A against a value of 4.4 mm (+/-2.4 mm, I SD) for the previously investigated non-immobilized patient group. Conclusions: Immobilization of the legs with an alpha-cradle system seems to improve both the accuracy and reproducibility of the positioning of patients treated for prostate cancer with respect to alpha-cradle pelvic-abdomen immobilization. Based on these data, we decided to use the legs immobilization system and to reduce the margin around the CTV (from 10 to 8 mm) in the PA direction. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved
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
Optical imaging of Tc-99m-based tracers: in vitro and in vivo results.
No full textIt has been recently shown that optical imaging (OI) methods can be used to image the in vivo biodistribution of several radiopharmaceuticals labeled with beta or alpha emitters. In this work particular attention has been focused on investigating the weaker optical signal induced by an almost pure gamma emitter like Tc-99m. Visible light emission measurements of a water solution containing Tc-99m were performed using a small animal OI system. A sequence of images was acquired for 24 h in order to study the decay of the luminescence signal. The difference between the luminescence decay half life and well-known Tc-99m half life was equal to 1\%. in vivo imaging was performed by injecting one control nude mice with Tc-99m-MDP. Optical images obtained with equipment designed for bioluminescence imaging showed that a visible light emission was distinguishable and correctly localized in the bladder region where a higher concentration of Tc-99m-MDP was expected. The bladder to background ratio was always greater than 1. We conclude that the experimental data presented in this paper show that it is possible to detect in vivo luminescence optical photons induced by Tc-99m. This is important especially considering the large number of Tc-99m-based radiopharmaceutical currently available
- …
