Current Issue : January - March Volume : 2016 Issue Number : 1 Articles : 5 Articles
Background: The high-resolution X-ray imaging system employing synchrotron\nradiation source, thin scintillator, optical lens and advanced CCD camera can achieve\na resolution in the range of tens of nanometers to sub-micrometer. Based on this\nadvantage, it can effectively image tissues, cells and many other small samples,\nespecially the calcification in the vascular or in the glomerulus. In general, the\nthickness of the scintillator should be several micrometers or even within\nnanometers because it has a big relationship with the resolution. However, it is\ndifficult to make the scintillator so thin, and additionally thin scintillator may greatly\nreduce the efficiency of collecting photons.\nMethods: In this paper, we propose an approach to extend the depth of focus\n(DOF) to solve these problems. We develop equation sets by deducing the\nrelationship between the high-resolution image generated by the scintillator and the\ndegraded blur image due to defect of focus first, and then we adopt projection onto\nconvex sets (POCS) and total variation algorithm to get the solution of the equation\nsets and to recover the blur image.\nResults: By using a 20 �¼m thick un matching scintillator to replace the 1 �¼m thick\nmatching one, we simulated a high-resolution X-ray imaging system and got a\ndegraded blur image. Based on the algorithm proposed, we recovered the blur\nimage and the result in the experiment showed that the proposed algorithm has\ngood performance on the recovery of image blur caused by un matching thickness\nof scintillator.\nConclusions: The method proposed is testified to be able to efficiently recover the\ndegraded image due to defect of focus. But, the quality of the recovery image\nespecially of the low contrast image depends on the noise level of the degraded\nblur image, so there is room for improving and the corresponding denoising\nalgorithm is worthy for further study and discussion....
We present the recently developed technique of Dark Field X-Ray Microscopy that\nutilizes the diffraction of hard X-rays from individual grains or subgrains at the (sub)micro metre scale\nembedded within mm-sized samples. By magnifying the diffracted signal, 3D mapping of\norientations and strains inside the selected grain is performed with an angular resolution of\n0.005o and a spatial resolution of 200 nm. Furthermore, the speed of the measurements at high intensity\nsynchrotron facilities allows for fast non-destructive in situ determination of structural\nchanges induced by annealing or other external influences. The capabilities of Dark Field X Ray\nMicroscopy are illustrated by examples from an ongoing study of recrystallization of 50%\ncold-rolled Al1050 specimens....
In this study, we have studied the effects of temperature and X-ray energy\nvariations on the light output signals from two different fiber-optic sensors, a fiber-optic\ndosimeter (FOD) based on a BCF-12 as a plastic scintillating fiber (PSF) and a fiber-optic\nthermometer (FOT) using a silver halide optical fiber as an infrared optical fiber (IR fiber).\nDuring X-ray beam irradiation, the scintillating light and IR signals were measured\nsimultaneously using a dosimeter probe of the FOD and a thermometer probe of the FOT.\nThe probes were placed in a beaker with water on the center of a hotplate, under variation\nof the tube potential of a digital radiography system or the temperature of the water in the\nbeaker. From the experimental results, in the case of the PSF, the scintillator light output at\nthe given tube potential decreased as the temperature increased in the temperature range\nfrom 25 to 60 Ã?°C. We demonstrated that commonly used BCF-12 has a significant\ntemperature dependence of âË?â??0.263 Ã?± 0.028%/Ã?°C in the clinical temperature range. Next, in\nthe case of the IR fiber, the intensity of the IR signal was almost uniform at each temperature\nregardless of the tube potential range from 50 to 150 kVp. Therefore, we also demonstrated\nthat the X-ray beam with an energy range used in diagnostic radiology does not affect the\nIR signals transmitted via a silver halide optical fiber....
X-ray phase-contrast tomography can significantly increase the contrast-resolution of conventional\nattenuation-contrast imaging, especially for soft-tissue structures that have very\nsimilar attenuation. Just as in attenuation-based tomography, phase contrast tomography\nrequires a linear dependence of aggregate beam direction on the incremental direction\nalteration caused by individual voxels along the path of the X-ray beam. Dense objects\nsuch as calcifications in biological specimens violate this condition. There are extensive\nbeam deflection artefacts in the vicinity of such structures because they result in large distortion\nof wave front due to the large difference of refractive index; for such large changes in\nbeam direction, the transmittance of the silicon analyzer crystal saturates and is no longer\nlinearly dependent on the angle of refraction. This paper describes a method by which\nthese effects can be overcome and excellent soft-tissue contrast of phase tomography can\nbe preserved in the vicinity of such artefact-producing structures....
In the early 1990s, Church and Takacs pointed out that the specification of surface figure and finish of\nx-ray mirrors must be based on their performance in the beamline optical system. We demonstrate the limitations\nof specification, characterization, and performance evaluation based on conventional statistical approaches,\nincluding root-mean-square roughness and residual slope variation, evaluated over spatial frequency bandwidths\nthat are system specific, and a more refined description of the surface morphology based on the\npower spectral density distribution. We show that these limitations are fatal, especially in the case of highly\ncollimated coherent x-ray beams, like beams from x-ray free electron lasers (XFELs). The limitations arise\ndue to the deterministic character of the surface profile data for a definite mirror, while the specific correlation\nproperties of the surface are essential for the performance of the entire x-ray optical system. As a possible\nway to overcome the problem, we treat a method, suggested by Yashchuk and Yashchuk in 2012, based on\nan autoregressive moving average modeling of the slope measurements with a limited number of parameters.\nThe effectiveness of the approach is demonstrated with an example specific to the x-ray optical systems under\ndesign at the European XFEL....
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