Search

Abstract: Diffraction Enhanced Imaging (DEI) derives X-ray contrast from absorption, refraction, and extinction. While the refraction angle image of DEI represents the gradient of the projected mass density of the object, the absorption image measures the projected attenuation () of an object. Using a simple integral method it has been shown that a mass density image () can be obtained from the refraction angle image. It then is a simple matter to develop a combinational image by dividing these two images to create a μ/ρ image. The μ/ρ is a fundamental property of a material and is therefore useful for identifying the composition of an object. In projection X-ray imaging the μ/ρ image identifies the integrated composition of the elements along the beam path. When applied to DEI computed tomography (CT), the image identifies the composition in each voxel. This method presents a new type of spectroscopy based in radiography. We present the method of obtaining the compositional image, the results of experiments in which we verify the method with known standards and an application of the method to breast cancer imaging. [Copyright &y& Elsevier]

Abstract: In the experimental setup for Diffraction Enhanced Imaging (DEI) and its extension, Multiple-Image Radiography (MIR), it is essential to have the two or three crystals angularly aligned relative to one another around two orthogonal axes; the angle around an axis perpendicular to the diffraction plane (the Bragg angle) and also around a perpendicular axis in the plane (azimuthal angle). The appearance of the azimuthal angle (tilt error) will complicate the interpretation of the DEI/MIR images by creating a systematic change in the Bragg angle across the width of the imaging beam which in turn creates intensity variations across the imaging field. In this paper we present the effect of a tilt error, its estimation from the resulting images, and a method to correct such an error for the DEI/MIR images. The analysis and results will also apply to multiple crystal systems with tilt errors, such as monochromators on synchrotron beamlines. [Copyright &y& Elsevier]

A new method of acquiring and analyzing diffraction-enhanced images (DEI) is presented. This method has been performed at the National Synchrotron Light Source and is based on using a novel two-crystal analyzer (Laue and Bragg analyzer). This system delivers simultaneously a pair of images with differing refraction sensitivity that is necessary for extracting absorption and refraction information using the DEI method. Although the system is not as flux efficient as a DEI system using a Bragg analyzer, it eliminates problems associated with object motion in between exposures. The system, method of interpreting the results and illustrative examples of experiments are presented and discussed. [Copyright &y& Elsevier]

Accurate measurement of the fat-to-muscle ratio in animal model is important for obesity research. An efficient way to measure the fat to muscle ratio in animal model using dual-energy absorptiometry is presented in this paper. A radioactive source exciting x-ray fluorescence from a target material is used to provide the two x-ray energies needed. The x-rays, after transmitting through the sample, are measured with an energy-sensitive Ge detector. Phantoms and specimens were measured. The results showed that the method was sensitive to the fat to muscle ratios with good linearity. A standard deviation of a few percent in the fat to muscle ratio could be observed with the x-ray dose of 0.001 mGy. [ABSTRACT FROM AUTHOR]

Abstract: In subcritical assemblies, the Bell and Glasstone spatial correction factor is used to correct the measured reactivity from different detector positions. In addition to the measuring position, several other parameters affect the correction factor: the detector material, the detector size, and the energy–angle distribution of source neutrons. The effective multiplication factor calculated by computer codes in criticality mode slightly differs from the average value obtained from the measurements in the different experimental channels of the subcritical assembly, which are corrected by the Bell and Glasstone spatial correction factor. Generally, this difference is due to (1) neutron counting errors; (2) geometrical imperfections, which are not simulated in the calculational model, and (3) quantities and distributions of material impurities, which are missing from the material definitions. This work examines these issues and it focuses on the detector choice and the calculation methodologies. The work investigated the YALINA Booster subcritical assembly of Belarus, which has been operated with three different fuel enrichments in the fast zone either: high (90%) and medium (36%), medium (36%), or low (21%) enriched uranium fuel. [Copyright &y& Elsevier]

Abstract: One of the most reliable experimental methods for measuring the subcriticality level of a nuclear fuel assembly is the Sjöstrand method applied to the reaction rate generated from a pulsed neutron source. This study developed a new analytical methodology simulating the Sjöstrand method, which allows comparing the experimental and analytical reaction rates and the obtained subcriticality levels. In this methodology, the reaction rate is calculated due to a single neutron pulse using MCNP/MCNPX computer code or any other neutron transport code that explicitly simulates the delayed fission neutrons. The calculation simulates a single neutron pulse over a long time period until the delayed neutron contribution to the reaction rate is vanished. The obtained reaction rate is then superimposed to itself, with respect to the time, to simulate the repeated pulse operation until the asymptotic level of the reaction rate, set by the delayed neutrons, is achieved. The superimposition of the pulse to itself was calculated by a simple C computer program. A parallel version of the C program is used due to the large amount of data being processed, e.g. by the Message Passing Interface (MPI). The analytical results of this new calculation methodology have shown an excellent agreement with the experimental data available from the YALINA-Booster facility of Belarus. This methodology can be used to calculate Bell and Glasstone spatial correction factor. [Copyright &y& Elsevier]

Abstract: Diffraction Enhanced Imaging (DEI) was used to characterize the extinction contrast coefficient of plant tissues. Single-cells were imaged with planar DEI. The organized structures of the plant cell walls were found to exhibit significant extinction contrast and were readily visualized using DEI. Extinction properties of different tissue types in plant roots, stems and seeds were characterized by DEI in Computed Tomography (DEI–CT) mode at the peak of the analyzer-rocking curve. DEI–CT yields different extinction coefficients for different cell types, resulting in high-contrast, high-resolution images of internal anatomical structures of plants. [Copyright &y& Elsevier]

Abstract: In an effort to explore Diffraction Enhanced Imaging of bone tissue, experiments were performed to determine if it was possible to use Diffraction Enhanced Imaging to detect microdamage in bovine cortical bone. Measurements were made at the National Synchrotron Light Source where pre- and post-fatigue rocking curve widths of the bone were studied. The rocking curve widths were then compared. Since no consistent pattern of narrowing or broadening of the rocking curve emerged, it is likely that the ultra-small-angle X-ray scattering present in the bone overshadowed any additional changes to rocking curve caused by microdamage of the bone. Larger bone structures were able to be visualized which suggests that microdamage may be visualized with a higher resolution detector. [Copyright &y& Elsevier]

Abstract: Irradiation with parallel arrays of thin, planar slices of X-ray beams (microplanar beams, or microbeams) spares normal tissue, including the central nervous system (CNS), and preferentially damages tumors. The effects are mediated, at least in part, by the tissue''s microvasculature that seems to effectively repair itself in normal tissue but fails to do so in tumors. Consequently, the therapeutic index of single-fraction unidirectional microbeam irradiations has been shown to be larger than that of single-fraction unidirectional unsegmented beams in treating the intracranial rat 9L gliosarcoma tumor model (9LGS) and the subcutaneous murine mammary carcinoma EMT-6. This paper presents results demonstrating that individual microbeams, or arrays of parallel ones, can also be used for targeted, selective cell ablation in the CNS, and also to induce demyelination. The results highlight the value of the method as a powerful tool for studying the CNS through selective cell ablation, besides its potential as a treatment modality in clinical oncology. [Copyright &y& Elsevier]

Abstract: Diffraction Enhanced Imaging (DEI) is an X-ray imaging method to provide additional contrast and diminish untoward image signals by reducing scattering. Previous reports demonstrated its applicability in soft and hard tissue imaging. Here we provide further evidence for the improved overall image quality and for the option to discriminate various tissue-specific properties, such as collagen fiber elements or mineralization. Comparative ex vivo data to medical MRI and to medical ultrasound are shown, utilizing human ankle and hip specimens. [Copyright &y& Elsevier]