2,069 research outputs found

    A coded-aperture technique allowing x-ray phase contrast imaging with conventional sources

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    Phase contrast imaging (PCI) solves the basic limitation of x-ray imaging, i.e., poor image contrast resulting from small absorption differences. Up to now, it has been mostly limited to synchrotron radiation facilities, due to the stringent requirements on the x-ray source and detectors, and only one technique was shown to provide PCI images with conventional sources but with limits in practical implementation. The authors propose a different approach, based on coded apertures, which provides high PCI signals with conventional sources and detectors and imposes practically no applicability limits. They expect this method to cast the basis of a widespread diffusion of PCI. (C) 2007 American Institute of Physics

    A simplified approach to quantitative coded aperture X-ray phase imaging

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    We recently demonstrated how quantitative X-ray phase contrast imaging may be performed with laboratory sources using the coded aperture technique. This technique required the knowledge of system parameters such as, for example, the source focal spot size and distances between elements of the imaging system. The method also assumes that the absorbing regions of the apertures are perfectly absorbing. In this paper we demonstrate how quantitative imaging can be performed without knowledge of individual system parameters and with partially absorbing apertures. We also show that this method is analogous to that employed in analyser based imaging which uses the rocking curve of an analyser crystal

    Edge-illumination x-ray phase-contrast imaging

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    Although early demonstration dates back to the mid-sixties, x-ray phase-contrast imaging (XPCI) became hugely popular in the mid-90s, thanks to the advent of 3rd generation synchrotron facilities. Its ability to reveal object features that had so far been considered invisible to x-rays immediately suggested great potential for applications across the life and the physical sciences, and an increasing number of groups worldwide started experimenting with it. At that time, it looked like a synchrotron facility was strictly necessary to perform XPCI with some degree of efficiency—the only alternative being micro-focal sources, the limited flux of which imposed excessively long exposure times. However, new approaches emerged in the mid-00s that overcame this limitation, and allowed XPCI implementations with conventional, non-micro-focal x-ray sources. One of these approaches showing particular promise for 'real-world' applications is edge-illumination XPCI: this article describes the key steps in its evolution in the context of contemporary developments in XPCI research, and presents its current state-of-the-art, especially in terms of transition towards practical applications

    Naturaleza y contenido esencial de la propuesta de “Ley reguladora de la actividad de la Administración y su control por los tribunales”

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    Olivo A. Rodríguez Huertas. Abogado dominicano, nacido en Higüey, La Altagracia. Es egresado de la Universidad Eugenio María de Hostos. Realizó un posgrado en fiscalidad internacional y una maestría en derecho de la contratación pública en la Universidad Castilla-La Mancha (Toledo), así como posgrados en derecho público y en derecho administrativo en las universidades San Pablo-CEU (Madrid) y de Salamanca, respectivamente. Ha desarrollado una amplio ejercicio profesional que lo ha llevado a desempeñarse, entre otros cargos, como asesor externo de la Procuraduría General de la República, miembro suplente de la Junta Electoral del Distrito Nacional, miembro de la Junta Directiva del Consejo Nacional de Drogas, consultor nacional del Programa de Apoyo a la Reforma y Modernización del Estado (PARME, auspiciado por la Unión Europea), contratista de la Agencia Internacional para el Desarrollo del gobierno de los Estados Unidos, presidente del Instituto Jurídico de la Unión Interamericana para la Vivienda (órgano asesor del Consejo Económico y Social de la Organización de las Naciones Unidas) y como miembro y coordinador general adjunto del grupo de expertos del Mecanismo de Evaluación Multilateral de la Comisión Interamericana para el Control del Abuso de Drogas de la OEA. Como catedrático universitario, ha sido profesor de Derecho Administrativo de la Universidad Iberoamericana (UNIBE) y de la Pontificia Universidad Católica Madre y Maestra (PUCMM), así como en el programa de máster en derecho de la administración del Estado coordinado por la Universidad de Salamanca y el Instituto Global de Altos Estudios en Ciencias Sociales de República Dominicana. Es coautor de las publicaciones Aspectos dogmáticos, procesales del lavado de activos, Documentos internacionales sobre lavado de activos, y Manual teórico práctico de libre acceso a la información pública. Recientemente fue designado embajador de la República Dominicana en España.Este es un artículo en el que se presenta una propuesta para regular, normar y controlar la actividad de la Administración en la República Dominicana. La iniciativa, que fuera resultado de las prioridades del Programa de Apoyo a la Reforma y Modernización del Estado (PARME) auspiciado por la Unión Europea, partía de la constatación de que en el Estado dominicano no existía para la fecha una normativa que sistematizara y reuniera los principios de la actividad de la Administración y de sus respectivos procesos (administrativo y contencioso-administrativo), los cuales se encontraban dispersos en diferentes instancias de la legislación nacional. Con dicho proyecto se pretendía articular un sistema claro y preciso de control administrativo y jurisdiccional que protegiera “eficazmente los derechos fundamentales de las personas” frente al poder estatal

    Absorption, refraction and scattering retrieval with an edge-illumination-based imaging setup

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    We have recently developed a new method based on edge-illumination for retrieving a three-image representation of the sample. A minimum of three intensity projections are required in order to retrieve the transmission, refraction and ultra-small-angle scattering properties of the sample. Here we show how the method can be adapted for particular cases in which some degree of a priori information about the sample might be available, limiting the number of required projections to two. Moreover, an iterative algorithm to correct for non-ideal optical elements is proposed and tested on numerical simulations, and finally validated on experimental data

    X-ray phase-contrast imaging with polychromatic sources and the concept of effective energy

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    Grating-based quantitative polychromatic x-ray phase imaging is currently a very active area of research. It has already been shown that, in such systems, the retrieved differential phase depends upon the spectral properties of the source, the gratings, the detector, and the sample. In this paper, we show that the retrieved sample absorption also depends upon the spectral properties of the gratings. Further, we compare the spectral dependence of both retrieved phase and absorption for the grating interferometer and coded aperture techniques. These results enable us to conclude that in both cases quantitative phase imaging systems cannot be described by an effective energy which is independent of the sample. This has important implications for applications where an absolute measure of phase is important and in tomography

    Virtual edge illumination and one dimensional beam tracking for absorption, refraction, and scattering retrieval

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    We propose two different approaches to retrieve x-ray absorption, refraction, and scattering signals using a one dimensional scan and a high resolution detector. The first method can be easily implemented in existing procedures developed for edge illumination to retrieve absorption and refraction signals, giving comparable image quality while reducing exposure time and delivered dose. The second method tracks the variations of the beam intensity profile on the detector through a multi-Gaussian interpolation, allowing the additional retrieval of the scattering signal

    A multi-layer edge-on single photon counting silicon microstrip detector for innovative techniques in diagnostic radiology

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    A three-layer detector prototype, obtained by stacking three edge-on single photon counting silicon microstrip detectors, has been developed and widely tested. This was done in the framework of the Synchrotron Radiation for Medical Physics/Frontier Radiology (SYRMEP/FRONTRAD) collaboration activities, whose aim is to improve the quality of mammographic examinations operating both on the source and on the detector side. The active surface of the device has been fully characterized making use of an edge-scanning technique and of a well-collimated laminar synchrotron radiation beam. The obtained data (interlayer distances, channel correspondence, etc.) have then been used to combine information coming from each detector layer, without causing any loss in spatial and contrast resolution of the device. Contrast and spatial resolution have also been separately evaluated for each detector layer. Moreover, imaging techniques (phase contrast, refraction, and scatter imaging), resulting in an increased visibility of low absorbing details, have been implemented, and their effectiveness has been tested on a biological sample. Finally, the possibility of simultaneously acquiring different kind of images with the different detector layers is discussed. This would result in maximizing the information extracted from the sample, while at the same time the high absorption efficiency of the detector device would allow a low dose delivery

    The Dexela 2923 CMOS X-ray detector: A flat panel detector based on CMOS active pixel sensors for medical imaging applications

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    Complementary metal-oxide-semiconductors (CMOS) active pixel sensors (APS) have been introduced recently in many scientific applications. This work reports on the performance (in terms of signal and noise transfer) of an X-ray detector that uses a novel CMOS APS which was developed for medical X-ray imaging applications. For a full evaluation of the detector's performance, electro-optical and X-ray characterizations were carried out. The former included measuring read noise, full well capacity and dynamic range. The latter, which included measuring X-ray sensitivity, presampling modulation transfer function (pMTF), noise power spectrum (NPS) and the resulting detective quantum efficiency (DQE), was assessed under three beam qualities (28 kV, 50 kV (RQA3) and 70 kV (RQA5) using W/Al) all in accordance with the IEC standard. The detector features an in-pixel option for switching the full well capacity between two distinct modes, high full well (HFW) and low full well (LFW). Two structured CsI:Tl scintillators of different thickness (a “thin” one for high resolution and a thicker one for high light efficiency) were optically coupled to the sensor array to optimize the performance of the system for different medical applications. The electro-optical performance evaluation of the sensor results in relatively high read noise (∼360 e−), high full well capacity (∼1.5×106 e−) and wide dynamic range (∼73 dB) under HFW mode operation. When the LFW mode is used, the read noise is lower (∼165) at the expense of a reduced full well capacity (∼0.5×106 e−) and dynamic range (∼69 dB). The maximum DQE values at low frequencies (i.e. 0.5 lp/mm) are high for both HFW (0.69 for 28 kV, 0.71 for 50 kV and 0.75 for 70 kV) and LFW (0.69 for 28 kV and 0.7 for 50 kV) modes. The X-ray performance of the studied detector compares well to that of other mammography and general radiography systems, obtained under similar experimental conditions. This demonstrates the suitability of the detector for both mammography and general radiography, with the use of appropriate scintillators. The high DQE values obtained under low mammographic exposures (up to 0.65 for 22.3 μGy) matches the demand for high detectability in imaging of the dense breast
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