Spectral CT reconstruction via low-rank representation and structure preserving regularization.

Objective:With the development of computed tomography (CT) imaging technology, it is possible to acquire multi-energy data by spectral CT. Being different from conventional CT, the X-ray energy spectrum of spectral CT is cut into several narrow bins which leads to the result that only a part of photon can be collected in each individual energy channel.This can severely degrade the image qualities. To address this problem, we propose a spectral CT reconstruction algorithm based on low-rank representation and structure preserving regularization in this paper.Approach:To make full use of the prior knowledge about both the inter-channel correlation and the sparsity in gradient domain of inner-channel data, this paper combines a low-rank correlation descriptor with a structure extraction operator as priori regularization terms for spectral CT reconstruction. Furthermore, a split-Bregman based iterative algorithm is developed to solve the reconstruction model. Finally, we propose a multi-channel adaptive parameters generation strategy according to CT values of each individual energy channel.Main results: Experimental results on numerical simulations and real mouse data indicate that the proposed algorithm achieves higher accuracy on both reconstruction and material decomposition than the methods based on simultaneous algebraic reconstruction technique (SART), total variation minimization (TVM), total variation with low-rank (LRTV), and spatial-spectral cube matching frame (SSCMF). Compared with SART, our algorithm improves the feature similarity (FSIM) by 40.4% on average for numerical simulation reconstruction, whereas TVM, LRTV, and SSCMF correspond to 26.1%, 28.2%, and 29.5%, respectively.Significance: We outline a multi-channel reconstruction algorithm tailored for spectral CT. The qualitative and quantitative comparisons present a significant improvement of image quality, indicating its promising potential in spectral CT imaging.

Heat Transfer Performance of Gel Foam Layer with Nanoparticles Doping under a Radiative Heat Flux.

The risk of fire in the chemical industry's production process is fatal. Gel foam has been widely employed in petroleum storage tanks, oil pools, and other petrochemical equipment for fire extinguishing and thermal protection. Recently, nanoparticles have been doped into gel foam to enhance thermal stability and insulation. However, heat transfer behaviors of the gel foam layer containing nanoparticles are still missing. In this study, a numerical heat transfer model of a gel foam layer containing silica nanoparticles under a radiative heat flux was established. Through simulation, the changes in foam thickness and temperature distribution were analyzed. The effects of the maximum heating temperature, initial gas content, nanoparticle size, and concentration on the thermal insulation behavior of the gel foam layer were systematically studied. The results showed that the thermal stability and insulation performance of the three-phase gel foam layer decreased with the increase in the initial gas content and particle size. Increasing the nanoparticle concentration could enhance the foam's thermal stability and insulation performance. The results provide guidance for a designing gel foam with high thermal protection performance.

X-ray source translation based computed tomography (STCT).

Micro computed tomography (µCT) allows the noninvasive visualization and 3D reconstruction of internal structures of objects with high resolution. However, the current commercial µCT system relatively rotates the source-detector or objects to collect projections, referred as RCT in this paper, and has difficulties in imaging large objects with high resolutions because fabrication of large-area, inexpensive flat-panel detectors remains a challenge. In this paper, we proposed a source translation based CT (STCT) for imaging large objects with high resolution to get rid of the limitation of the detector size, where the field of view is primarily determined by the source translation distance. To compensate for the deficiency of incomplete data in STCT, we introduced multi-scanning STCT (mSTCT), from which the projections theoretically meet the conditions required for accurate reconstructions. Theoretical and numerical studies showed that mSTCT has the ability to accurately image large objects without any visible artifacts. Numerical simulations also indicated that mSTCT has a potential capability to precisely image the region of interest (ROI) inside objects, which remains a challenge in RCT due to truncated projections. In addition, an experimental platform for mSTCT has been established, from which the 2D and 3D reconstructed results demonstrated its feasibility for µCT applications. Moreover, STCT also has a great potential for security inspection and product screening by using two perpendicular STCTs, with advantages of low-cost equipment and high-speed examination.

3D X-ray micro-computed tomography imaging for the microarchitecture evaluation of porous metallic implants and scaffolds.

As an advanced microscopy technology with strong sample adaptability and non-destructive three-dimensional (3D) characteristics, X-ray micro-computed tomography (Micro-CT) can establish the overall connection between various microarchitecture parameters and accelerate the research process of porous metallic implants and scaffolds. In this review, the Micro-CT based quantitative evaluation methods of microarchitecture and bone formation are investigated. To ensure reliability of the results, the Micro-CT setup is discussed briefly and the essential image processing algorithms are introduced in detail. The significance and limitations of Micro-CT are analyzed in the context of research on porous metallic implants. We also discuss the future development of Micro-CT technology in the field of biological tissue engineering.

Ring-artifacts removal for photon-counting CT.

Ring artifacts usually appear in photon counting computed tomography (PCCT) images, which may compromise image quality and cause non-uniformity bias. This study proposed a fast ring artifacts removal method by exploring the correlation from projections with different views for PCCT. This method has three advantages. First, our method only employ mean projection of current scan to correct projections without additional scans. Second, our method can correct the inconsistency of all detector pixels simultaneously without locating the inconsistent response pixels. Third, it can preserve reconstructed image details well without extra computational cost. Both numerical and preclinical experiments demonstrate the proposed method can suppress the ring artifacts very well than the competitors.

Migration and Adherence of Oil Droplets on Surfaces with Different Wettability in a Laminar Flow Field.

In this article, the rising trajectories of oil droplets near the substrates of small channels in the laminar flow field were observed using a high-speed camera. Chemical modifications were made on the surfaces of the brass sheets to change the surface properties, and the controllable regulation of the superoleophilic-superoleophobic wettability gradient was achieved. The adhesion behaviors of the oil droplets on surfaces with different wettabilities at different flow velocities were observed as well. According to the adhesion behaviors of oil droplets on surfaces with different wettabilities, a mathematical model was established to analyze water film thinning and the adherence of oil droplets on the wall in the laminar flow field. Then the quantitative relationships among the adhesion times tf of oil droplets on different wetting surfaces, oil and water properties, and surface wettability were acquired.

Study of the Microfocus X-Ray Tube Based on a Point-Like Target Used for Micro-Computed Tomography.

For a micro-Computed Tomography (Micro-CT) system, the microfocus X-ray tube is an essential component because the spatial resolution of CT images, in theory, is mainly determined by the size and stability of the X-ray focal spot of the microfocus X-ray tube. However, many factors, including voltage fluctuations, mechanical vibrations, and temperature changes, can cause the size and the stability of the X-ray focal spot to degrade. A new microfocus X-ray tube based on a point-like micro-target in which the X-ray target is irradiated with an unfocused electron beam was investigated. EGS4 Monte Carlo simulation code was employed for the calculation of the X-ray intensity produced from the point-like micro-target and the substrate. The effects of several arrangements of the target material, target and beam size were studied. The simulation results demonstrated that if the intensity of X-rays generated at the point-like target is greater than half of the X-ray intensity produced on the substrate, the X-ray focal spot is determined in part by the point-like target rather than by the electron beam in the conventional X-ray tube. In theory, since it is able to reduce those unfavorable effects such as the electron beam trajectory swinging and the beam size changing for the microfocus X-ray tube, it could alleviate CT image artifacts caused by the X-ray focal spot shift and size change.

Study of solid-conversion gaseous detector based on GEM for high energy X-ray industrial CT.

The general gaseous ionization detectors are not suitable for high energy X-ray industrial computed tomography (HEICT) because of their inherent limitations, especially low detective efficiency and large volume. The goal of this study was to investigate a new type of gaseous detector to solve these problems. The novel detector was made by a metal foil as X-ray convertor to improve the conversion efficiency, and the Gas Electron Multiplier (hereinafter "GEM") was used as electron amplifier to lessen its volume. The detective mechanism and signal formation of the detector was discussed in detail. The conversion efficiency was calculated by using EGSnrc Monte Carlo code, and the transport course of photon and secondary electron avalanche in the detector was simulated with the Maxwell and Garfield codes. The result indicated that this detector has higher conversion efficiency as well as less volume. Theoretically this kind of detector could be a perfect candidate for replacing the conventional detector in HEICT.

[Beam hardening simulated correction research for X-ray TICT in testing composites workpiece].

In X-ray TICT, when X-ray is transmitted in the materal, the phenomenon of energy spectrum hardening takes place, resulting in artifacts. Thus, hardening correction has to be done. In the present paper, the phenomenon of X-ray beam hardening resulting in analyized, and the relation between the X-ray beam sum and the transmission thickness in testing composites workpiece is discussed. According to the Beer law and the characteristics of the interaction between X-ray and the material, and getting the data of X-ray beam sum, the relation equation between the beam sum and transmission thickness is simulated firstly, and testing composites workpiece. Then, the relation and the method of equivalence are carried out between the equivalent transmission thickness and the transmission thickness for X-ray beam sum being corrected for monochromatic ray beam. Finally, the attenuation coefficient beam hardening simulated value for X-ray equivalent monochromatic is reasoned out in testing composites workpiece. Then, the attenuation coefficient simulated value that has been corrected is used for product back-projection reconstruction. Thus, the effect caused by X-ray beam hardening is wipped off effectively in testing composites workpiece.