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

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

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

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

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

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

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

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

Phase Contrast Imaging with Coded Apertures Using Laboratory-Based X-ray Sources

X‐ray phase contrast imaging is a powerful technique that allows detection of changes in the phase of x‐ray wavefronts as they pass through a sample. As a result, details not visible in conventional x‐ray absorption imaging can be detected. Until recently the majority of applications of phase contrast imaging were at synchrotron facilities due to the availability of their high flux and coherence; however, a number of techniques have appeared recently that allow phase contrast imaging to be performed using laboratory sources. Here we describe a phase contrast imaging technique, developed at University College London, that uses two coded apertures. The x‐ray beam is shaped by the pre‐sample aperture, and small deviations in the x‐ray propagation direction are detected with the help of the detector aperture. In contrast with other methods, it has a much more relaxed requirement for the source size (it works with source sizes up to 100 μm). A working prototype coded‐aperture system has been built. An x‐ray detector with directly deposited columnar CsI has been used to minimize signal spill‐over into neighboring pixels. Phase contrast images obtained with the system have demonstrated its effectiveness for imaging low‐absorption materials

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

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

Edge-illumination X-ray dark-field imaging for visualising defects in composite structures

Low velocity impact can lead to barely visible and difficult to detect damage such as fibre and matrix breakage or delaminations in composite structures. Drop-weight impact damage in a cross-ply carbon fibre laminate plate was characterized using ultrasonic C-scan measurements. This was compared to the results provided by a novel X-ray imaging technique based on the detection of phase effects, which can be implemented with conventional equipment. Three representations of the sample are provided: absorption, differential phase and dark-field. The latter is of particular interest to detect cracks and voids of dimensions that are smaller than the spatial resolution of the imaging system. The ultrasonic C-scan showed a large delamination and additional damage along the fibre directions. The damage along the fibre directions and other small scale defects were detected from the X-ray imaging. As the system is sensitive to phase effects along one direction at a time, the acquisition of an additional scan, rotating the sample 90 degrees around the beam axis, provides information in both fibre directions. These two techniques enable access to a set of complementary information, across different length scales, which can be useful in the characterization of the defects occurring in composite structures