1,721,114 research outputs found
GEANT4 simulation of a 3D Compton imaging device
No full textA 3D brain imaging device based on Compton scattering is investigated with
a GEANT4 Monte-Carlo simulation. The proposed device relies on a novel 3D
imaging technique which, contrary to other approaches like Compton
cameras, does not require any backprojection procedure. We study the
attainable sensitivity in the detection of density variations as a
function of the beam energy, the depth inside the object and size and
density of the inclusions. At midbrain position a resolution of about 2 mm
and a contrast of 12% are obtained. In addition the simulation indicates
that a complete brain scan at 600 keV beam energy would result in an
effective dose of about 1 mSv
Monte Carlo study of a 3D Compton imaging device with GEANT4
Full text linkIn this paper we investigate, with a detailed Monte Carlo simulation based on Geant4, the novel approach of Lenti (2008) [1] to 3D imaging with photon scattering. A monochromatic and well collimated gamma beam is used to illuminate the object to be imaged and the photons Compton scattered are detected by means of a surrounding germanium strip detector. The impact position and the energy of the photons are measured with high precision and the scattering position along the beam axis is calculated. We study as an application of this technique the case of brain imaging but the results can be applied as well to situations where a lighter object, with localized variations of density, is embedded in a denser container. We report here the attainable sensitivity in the detection of density variations as a function of the beam energy, the depth inside the object and size and density of the inclusions. Using a 600 key gamma beam, for an inclusion with a density increase of 30% with respect to the surrounding tissue and thickness along the beam of 5 mm, we obtain at midbrain position a resolution of about 2 mm and a contrast of 12%. In addition the simulation indicates that for the same gamma beam energy a complete brain scan would result in an effective dose of about 1 mSv
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
Osteochondromas: An Unusual Cause of Vascular Disease in Young Patients: 2 Clinical Cases
No full textOsteochondroma is the most common benign tumor of bones in young patients. It is an unusual cause of nonatherosclerotic peripheral arteriopathy. It is mostly detected in youth and, thus, diagnosis can be delayed since symptoms such as claudication can be confused with muscular cramps. In case of clinical suspicion of peripheral artery disease in the young, the presence of an exostosis should be suspected. We reported our experience of 2 young patients with limb ischemia due to ab extrinseco compression of popliteal artery. In both cases, surgical exeresis of a lower limb exostosis was performed. In the first case, bypass surgery was not required since arterial wall was not damaged. In the second case, an autologous inverted saphenous vein femoro popliteal bypass was performed
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
The effect of manufacturer's instructions for use compliance on Cook ZBIS iliac-branched endograft long term outcomes
No full textCurrent guidelines indicate iliac branched endografts as the ideal means to preserve pelvic perfusion during endovascular aortic repair. Since patient vascular anatomy represents the main limitation to extensive use of these devices, off-label application may be considered to expand the number of patients being treated. Aim of this study is to evaluate long-term outcomes obtained using the Cook ZBIS endograft in the treatment of aorto-iliac aneurysms according to or outside manufacturer's instruction for use
Pulmonary sequestration supplied by giant aneurysmal aortic branch
No full textWe report a case of an intralobar sequestration supplied by a 13-cm aneurysmal vessel originating from the abdominal aorta. The malformation was discovered during a roentgenogram investigation of an abdominal infrarenal aneurysm. During the endovascular repair of the abdominal aneurysm, the giant feeding vessel of the pulmonary sequestration was embolized. Two days later the patient underwent an uneventful resection of the malformation en bloc with the right lower lobe through a standard right thoracotomy. (Ann Thorac Surg 2010;89:e7-8) (C) 2010 by The Society of Thoracic Surgeon
Sarcoma of the Thigh: Radical Excision with Arterial Reconstruction Using the Contralateral Saphenous Vein
No full textSoft tissue sarcomas are a heterogeneous group of malignant mesenchymal neoplasms that frequently affect large muscle of the thigh. A conservative limb-salvage surgery involving en bloc resection of the whole tumor with surrounding healthy tissue can sometimes be considered instead of amputation to achieve good local disease control while preserving a satisfying function of the
affected limb.
The massive vascular encasement, once regarded as a contraindication to limb-salvage surgery, can sometimes be
encompassed thanks to vascular axis reconstruction.
Although no doubt exists about the need for reconstruction of the femoral artery with quite good reported results, the
venous replacement is a controversial issue with unclear patency rates, yet this replacement is mandatory when
superficial and deep femoral veins are removed together with the saphenous vein. The femoral artery is commonly
replaced with an autologus reversed saphenous vein graft because of its resistance to infections and its excellent
patency rates compared with artificial grafts.
We present a case of thigh sarcoma involving the femoral vascular axis with complete clogging of the
femoral vein due to massive deep thrombosis. The video illustrates the features of the case and highlights the steps
of a wide compartment resection with arterial reconstruction by autologus reversed saphenous vein graft
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