1,720,996 research outputs found
Operator radiation doses during CT-guided spine procedures
No full textObjectives: To perform a pilot study to quantify the radiation dose incident on operators during CT-guided interventional spine procedures, and provide a quick method to approximate it based on the total amount of radiation reported by the CT scanner. Patients and Methods: Data retrospectively obtained from 26 consecutive CT-guided spine procedures, encompassing a variety of interventions. Intermittent low-dose limited-coverage CT-scanning performed using a “step and shoot” mode to visualize needle advancement. The operator wore an electronic direct dosimeter to record the dose measured above the operator's lead apron [μGy] for each procedure. Total amount of radiation used for CT-guidance quantified by the Dose-Length Product (DLP) [mGy-cm] provided by the CT scanner. The relationship between the operator's dose and the DLP was assessed. Results: Average and median operator's dose were 2.3 and 1.9 μGy, respectively, with half of these values ranging between 0.7 and 2.5 μGy. Average and median DLP values used to perform the CT-guided procedure were 58 and 54 mGy-cm respectively, and half of these values ranged between 38 and 68 mGy-cm. There was a statistically significant correlation between the operator's dose and the DLP used to perform CT-guidance (r = 0.61), with an operator's dose-DLP conversion factor of 0.04 μGy / 1 mGy-cm (range: 0.006-0.083 μGy / 1 mGy-cm). Conclusions: In our series, the average amount of radiation used during CT guided procedures was about 50 mGy-cm (DLP), and the corresponding average operator's dose was about 2 μGy. We showed how an approximate estimate of the operator's dose could be obtained right after each procedure, based on the CT-scanner DLP output
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
Stent Screw−Assisted Internal Fixation (SAIF) of Severe Lytic Spinal Metastases: A Comparative Finite Element Analysis of the SAIF Technique
No full textOBJECTIVE: A new stent-screw - assisted internal fixation (SAIF) minimally invasive cement-augmentation technique has been introduced to treat patients with extreme osteolytic lesions of the vertebral body. The aim of the current finite element study, employing a spine model with an extreme osteolytic defect, was to assess the effect of the SAIF technique in reducing strains in the vertebral body in comparison with a standard surgical short posterior fixation.METHODS: Different finite element models of a L1-S1 spine were developed, representing an intact condition (reference configuration), an extreme osteolysis condition, and its treatment, respectively with stand-alone SAIF, SAIF and posterior fixation, and with stand-alone posterior fixation. Each model was loaded to reproduce standing and upper body bending. Principal strains were calculated on the superior endplate, anterior and posterior cortical walls. A paired Wilcoxon test with a 0.05 significance level was performed to statistically analyze the results.RESULTS: Median strains on the bony structures increased in the osteolysis model compared with the intact model, and the SAIF technique was effective in reducing such strains under both standing and flexion conditions. Additional posterior fixation, combined with the SAIF technique, produced minimal further reduction of the median strains on the bony structures. Stand-alone posterior fixation only shielded the osteolytic vertebra avoiding excessive displacements but failed in restoring the axial stiffness to values typical of the intact vertebra.CONCLUSIONS: The new SAIF technique resulted effective in restoring the load-bearing capacity of the extensively osteolytic vertebra; additional posterior fixation provided only further minor advantages
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
Magnetic resonance imaging of pilocytic astrocytomas in adults with histopathologic correlation: a report of six consecutive cases
No full textPilocytic astrocytoma is a WHO grade I tumor usually diagnosed in pediatric patients, and rarely encountered in the adult population. Therefore, available information about the magnetic resonance imaging characteristics of adult pilocytic astrocytoma is scarce. We report on the MRI features and corresponding histopathologic findings of six consecutive aPA cases diagnosed. The tumors were encountered in both infra- and supratentorial compartments, and their MRI characteristics were quite heterogeneous. Features included the typical solid-cystic appearance located in the cerebellum as well as the relatively unusual multifocal and/or hemorrhagic features located intra-ventricularly. The aPA MRI characteristics are remarkably variable, and might mimic those of higher grade tumors in adult patients
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