Current Issue : April - June Volume : 2017 Issue Number : 2 Articles : 5 Articles
Background: In hard X-ray phase imaging using interferometry, the spatial resolution is limited by the pixel size of\ndigital sensors, inhibiting its use in magnifying observation of a sample.\nMethods: To solve this problem, we describe a digital phase contrast microscope that uses Zernikeâ��s phase contrast\nmethod with a hard X-ray Gabor holography associated with numerical processing and spatial frequency domain filtering\ntechniques. The hologram is reconstructed by a collimated beam in a computer. The hologram intensity distributions\nitself become the reconstructed wavefronts. For this transformation, the Rayleigh- Sommerfeld diffraction formula is used.\nResults: The hard X-ray wavelength 0.1259 nm (an energy of 9.85 keV) was employed at the SPring-8 facility. We\nsucceeded in obtaining high-resolution images by a CCD sensor with a pixel size of 3.14 �¼m, even while bound by the\nneed to satisfy the sampling theorem and by the CCD pixel size. The test samples used here were polystyrene beads of 8\n�¼m, and human HeLa cells.\nConclusions: We thus proved that the resolution 0.951 �¼m smaller than the pixel size of CCD (3.14 �¼m) was achieved by\nthe proposed reconstruction techniques and coherent image processing in the computer, suggesting even higher\nresolutions by adopting greater numerical apertures....
Microbeam radiation therapy is an innovative treatment approach in radiation therapy that\nuses arrays of a few tens of micrometer wide and a few hundreds of micrometer spaced planar\nx-ray beams as treatment fields. In preclinical studies these fields efficiently eradicated tumors\nwhile normal tissue could effectively be spared. However, development and clinical application of\nmicrobeam radiation therapy is impeded by a lack of suitable small scale sources. Until now, only\nlarge synchrotrons provide appropriate beam properties for the production of microbeams.\nMethods: In this work, a conventional x-ray tube with a small focal spot and a specially designed\ncollimator are used to produce microbeams for preclinical research. The applicability of the developed\nsource is demonstrated in a pilot in vitro experiment. The properties of the produced radiation field\nare characterized by radiochromic film dosimetry.\nResults: 50 Ã?¼m wide and 400 Ã?¼m spaced microbeams were produced in a 20Ã?â??20 mm2 sized\nmicrobeam field. The peak to valley dose ratio ranged from 15.5 to 30, which is comparable to\nvalues obtained at synchrotrons. A dose rate of up to 300 mGy/s was achieved in the microbeam\npeaks. Analysis of DNA double strand repair and cell cycle distribution after in vitro exposures of\npancreatic cancer cells (Panc1) at the x-ray tube and the European Synchrotron leads to similar results.\nIn particular, a reduced G2 cell cycle arrest is observed in cells in the microbeam peak region.\nConclusions: At its current stage, the source is restricted to in vitro applications. However, moderate\nmodifications of the setup may soon allow in vivo research in mice and rats....
For the last several years, the linear array x-ray detector for x-ray imaging with gallium\narsenide direct conversion sensitive elements has been developed and tested at\nthe Institute for High Energy Physics. The array consists of 16 sensitive modules.\nEach module has 128 gallium arsenide (GaAs) sensitive elements with 200 �¼m pitch.\nCurrent article describes two key program procedures of initial dark current compensation\nof each sensitive element in the linear array, and sensitivity adjustment for\nalignment of strip pattern in the raw image data. As a part of evaluation process a\nmodular transfer function (MTF) was measured with the slanted sharp-edge object\nunder RQA5 technique as it described in the International Electrotechnical Commission\n62220-1 standard (high voltage 70 kVp, additional aluminium filter 21 mm) for\nimages with compensated dark currents and adjusted sensitivity of detector elements.\nThe 10% level of the calculated MTF function has spatial resolution within 2 - 3 pair\nof lines per mm for both vertical and horizontal orientation....
The application of organic electronic materials for the detection of ionizing radiations is very\nappealing thanks to their mechanical flexibility, low-cost and simple processing in comparison\nto their inorganic counterpart. In this work we investigate the direct X-ray photoconversion\nprocess in organic thin film photoconductors. The devices are realized by drop casting\nsolution-processed bis-(triisopropylsilylethynyl)pentacene (TIPS-pentacene) onto flexible\nplastic substrates patterned with metal electrodes; they exhibit a strong sensitivity to X-rays\ndespite the low X-ray photon absorption typical of low-Z organic materials. We propose a\nmodel, based on the accumulation of photogenerated charges and photoconductive gain, able\nto describe the magnitude as well as the dynamics of the X-ray-induced photocurrent.\nThis finding allows us to fabricate and test a flexible 22 pixelated X-ray detector operating\nat 0.2V, with gain and sensitivity up to 4.7104 and 77,000 nC mGy1 cm3, respectively....
Current technologies for X-ray detection rely on scintillation from expensive inorganic crystals grown at high-temperature, which so far has hindered the development of large-area scintillator arrays. Thanks to the presence of heavy atoms, solution-grown hybrid lead halide perovskite single crystals exhibit short X-ray absorption length and excellent detection efficiency. Here we compare X-ray scintillator characteristics of three-dimensional (3D) MAPbI3 and MAPbBr3 and two-dimensional (2D) (EDBE)PbCl4 hybrid perovskite crystals. X-ray excited thermoluminescence measurements indicate the absence of deep traps and a very small density of shallow trap states, which lessens after-glow effects. All perovskite single crystals exhibit high X-ray excited luminescence yields of >120,000 photons/MeV at low temperature. Although thermal quenching is significant at room temperature, the large exciton binding energy of 2D (EDBE)PbCl4 significantly reduces thermal effects compared to 3D perovskites, and moderate light yield of 9,000 photons/MeV can be achieved even at room temperature. This highlights the potential of 2D metal halide perovskites for large-area and low-cost scintillator devices for medical, security and scientific applications....
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