Phase retrieval with unidirectional differential phase-contrast image requires integration with noisy data, which is an illposed inverse problem. Conventional direct integration method would result in severe streak artifacts. Total variation (TV) regularization-based method would reduce the streak artifacts, but the edges parallel with phase-contrast sensitivity direction are likely to be over smoothed. We propose an improved weighted TV regularization phase retrieval method by introducing a weighting factor to the conventional TV term. When applied to simulation and experimental data, this method shows an advantage of preserving the sharpness of the edges while preserving the ability of reducing streak artifacts compared with conventional TV-regularization method.
X-ray phase-contrast imaging has experienced rapid development over the last few decades, and, in this technology, the phase modulation strategy of phase stepping (PS) is used most widely to measure the sample’s phase signal. However, because of its discontinuous nature, PS has the defects of worse mechanical stability and high exposure dose, which greatly hinder its wide use in dynamic phase measurement and potential clinical applications. We demonstrate preliminary research on the use of integrating-bucket (IB) phase modulation method to retrieve the phase information in grating-based x-ray phase-contrast imaging. Experimental results show that our proposed method can be well employed to extract the differential phase-contrast image, compared with the commonly used PS strategy, the advantage of the IB phase modulation technique is that fast measurement and low dose are promising.
Carbon fiber composites have been wildly used in aerospace industry due to the excellent performance. However, the research on defect evolution law and the performance analysis have been limited by the lack of effective tools. Two kinds of computed tomography (CT) slice images of carbon fiber composites, x-ray attenuation contrast and phase contrast, were obtained with the diffraction enhancement imaging (DEI) device at Beijing Synchrotron Radiation Facility (BSRF). The structure details and the defects in the sample could be clearly distinguished from the image. Moreover, phase contrast CT provides higher contrast and can identify the defects difficult to be recognized in attenuation contrast CT. DEI provides a method for in-situ observation of the carbon fiber composites and would be a valuable tool for the development of carbon fiber composite material.
With the progresses of material sciences and technologies, carbon fiber composite shell-plate structures have been widely used in aerospace industry. Suffering from the drastic change of penetration thickness during the 360°scanning, conventional computed tomography (CT) is difficult to be applied to this kind of structures with a big length-width-thickness ratio, and not easy to implement the defect detection and the performance analysis. Based on the existing diffraction enhanced imaging (DEI) device at Beijing Synchrotron Radiation Facility beam-line 4W1A, a new computed laminography (CL) scanning system was designed and developed. It was integrated with the DEI device to form a synchrotron radiation DEI-CL system for plate-shell structures. Within this system, the components such as light source, detector and turntable and the working principle were discussed in detail. The experiment results of a decimeter-scale carbon fiber composite laminate sample validate the developed scanning system.