1,720,996 research outputs found
Microbubbles as x-ray scattering contrast agents using analyzer-based imaging
No full textConventional contrast agents utilized in diagnostic radiology are based on x-ray absorption properties; alternative physical principles capable of providing a contrast enhancement in radiographs have never been applied. This study exploits the possibility of using a novel type of contrast media based on x-ray scattering. The contrast agents consist of microbubble echo-enhancing agents, usually applied in ultrasound examinations, which are invisible with conventional x-ray absorption techniques. The experiment was carried out at the medical beamline of the synchrotron radiation laboratory ELETTRA in Trieste, Italy. A flat silicon analyzer crystal typically used for diffraction-enhanced imaging was utilized as a tool for detecting the scattering properties of the contrast agents. In analyzer-based imaging, it is possible to detect the scattering properties of the sample by shifting the analyzer crystal to selected positions of its reflectivity curve. In particular, when the sample consists of a large number of micro-particles an overall effect can be observed. Phantoms containing contrast agents based on microbubbles were imaged at different angular positions of the analyzer crystal. High visibility of the details was demonstrated, and a strong contrast enhancement was measured compared to normal x-ray absorption techniques
X-ray cell tracking: from ex-vivo to in-vivo experiments
No full textThe capacity to track cells (cell tracking) using x-rays on ex-vivo specimens of both malignant and non-malignant cell lines on small animals has been demonstrated recently. Gold nanoparticles have been used as a cellular contrast agent to render cells visible in x-ray microCT acquisitions. The limits of the technique proposed are basically driven by the imaging system used. Single cell resolution can be achieved using synchrotron radiation in-vitro or ex-vivo samples. Micro-focus x-ray tubes can be used to obtain high resolution cell tracking but with some limitations. However, the translation from ex-vivo to in-vivo experiments is not straightforward. The dose restrictions required for in-vivo longitudinal experiments set severe limitations on the technique. Here we present a detailed investigation showing a significant reduction of x-ray dose for the tracking of brain tumour cells. Monte Carlo simulations have been performed considering different spatial resolutions, photon fluence, number of projections, lesion dimension and cell contrast dilution. The findings are compared with real samples imaged using the same parameters. A pioneering in-vivo experiment conducted at the SYRMEP beamline (Elettra, Basovizza, Italy) is presented here as proof of principle of in-vivo longitudinal x-ray cell tracking experiments on small animals at low x-ray doses
Fast, multi-wavelength, efficiency-enhanced pixelated devices based on InGaAs/InAlAs quantum-well
No full textSeveral applications utilizing either synchrotron or conventional light sources require fast and efficient pixelated detectors. In order to cover a wide range of experiments, this work investigates the possibility to use InGaAs/InAlAs quantum well devices as photon detectors for a broad range of energies.
Owing to their direct, low-energy band gap and high electron mobility, such devices may be used also at room temperature as multi-wavelength sensors from visible light to hard X-rays. Furthermore, internal charge-amplification mechanism can be applied for very low signal levels, while the high carrier mobility allows the design of very fast photon detectors with sub-nanosecond response times.Samples were grown by solid source molecular beam epitaxy on GaAs substrates. Metamorphic In0.75Ga0.25As/ In0.75Al0.25As heterostructures were obtained by relaxing the strain due to the lattice mismatch in the substrate by means of a composition-graded buffer layer. A two-dimensional electron gas forming in an In0.75Ga0.25As quantum well is sandwiched between In0.75Al0.25As barriers and is modulation-doped by a Si δ on its top. The samples have been pixelated by using standard photolithographic techniques. In order to fit commercially available readout chips, a pixelated sensor with pixel size of 172 × 172 μ m2 is currently under development. A small-scale version of the pixelated quantum well sensor has been preliminary tested with 100-fs-wide laser pulses and X-ray synchrotron radiation. The reported results indicate that these sensors respond with 100-ps rise-times to ultra-fast laser pulses. Synchrotron X-ray tests show how these devices exhibit high charge collection efficiencies, which can be imputed to the charge-multiplication effect of the 2D electron gas inside the well
Can we develop an early warning system for patients after cell transplantation therapy using X-ray imaging?
No full textOver the last decades, several new therapeutic concepts which include the transplantation of cells have been developed for diseases of the central nervous system (CNS). The migration of implanted cells away from the intended transplantation site as well as tumour formation from unchecked cell proliferation are potential risks of such therapeutic approaches. In order to follow cell migration and possibly proliferation we have developed a technique that allows detection and tracking of implanted cells which have been marked with gold nanoparticles (GNPs) prior to implantation into the host organism. The GNP-loaded cells provide sufficient contrast to be detected with synchrotron X-ray imaging methods. Very small cell clusters and even individual cells can be detected. The price for the high spatial resolution is the exposure of implanted cells and host organism to comparably high radiation doses during the imaging procedures. Therefore, before advocating use of the technique to follow up larger series of transplantation experiments in small animal models of CNS disease it is absolutely mandatory to obtain experimental evidence regarding the threshold X-ray dose above which single or repeated imaging would interfere with the functionality of GNP-loaded cells. Only once this question has been answered should the possibility to develop this method towards clinical application be considered
External and internal structure of weevils (Insecta: Coleoptera) investigated with phase-contrast X-ray imaging
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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
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