Analysis of algebraic reconstruction technique for accurate imaging of gas temperature and concentration based on tunable diode laser absorption spectroscopy

An improved algebraic reconstruction technique（ART） combined with tunable diode laser absorption spectroscopy（TDLAS） is presented in this paper for determining two-dimensional（2D） distribution of H2O concentration and temperature in a simulated combustion flame.This work aims to simulate the reconstruction of spectroscopic measurements by a multi-view parallel-beam scanning geometry and analyze the effects of projection rays on reconstruction accuracy.It finally proves that reconstruction quality dramatically increases with the number of projection rays increasing until more than 180 for 20 × 20 grid,and after that point,the number of projection rays has little influence on reconstruction accuracy.It is clear that the temperature reconstruction results are more accurate than the water vapor concentration obtained by the traditional concentration calculation method.In the present study an innovative way to reduce the error of concentration reconstruction and improve the reconstruction quality greatly is also proposed,and the capability of this new method is evaluated by using appropriate assessment parameters.By using this new approach,not only the concentration reconstruction accuracy is greatly improved,but also a suitable parallel-beam arrangement is put forward for high reconstruction accuracy and simplicity of experimental validation.Finally,a bimodal structure of the combustion region is assumed to demonstrate the robustness and universality of the proposed method.Numerical investigation indicates that the proposed TDLAS tomographic algorithm is capable of detecting accurate temperature and concentration profiles.This feasible formula for reconstruction research is expected to resolve several key issues in practical combustion devices.

Gray weighted algorithm for variable voltage CT reconstruction

In conventional computed tomography （CT） reconstruction based on fixed voltage, the projective data often ap- pear overexposed or underexposed, as a result, the reconstructive results are poor. To solve this problem, variable voltage CT reconstruction has been proposed. The effective projective sequences of a structural component are obtained through the variable voltage. The total variation is adjusted and minimized to optimize the reconstructive results on the basis of iterative image using algebraic reconstruction technique （ART）. In the process of reconstruction, the reconstructive image of low voltage is used as an initial value of the effective proiective reconstruction of the adjacent high voltage, and so on until to the highest voltage according to the gray weighted algorithm. Thereby the complete structural information is reconstructed. Simulation results show that the proposed algorithm can completely reflect the information of a complicated structural com- ponent, and the pixel values are more stable than those of the conventional.

Ultrahigh spatiotemporal resolution beam signal reconstruction with bunch phase compensation

Various electromagnetic signals are excited by the beam in the acceleration and beam-diagnostic elements of a particle accelerator.It is important to obtain time-domain waveforms of these signals with high temporal resolution for research,such as the study of beam–cavity interactions and bunch-by-bunch parameter measurements.Therefore,a signal reconstruction algorithm with ultrahigh spatiotemporal resolution and bunch phase compensation based on equivalent sampling is proposed in this paper.Compared with traditional equivalent sampling,the use of phase compensation and setting the bunch signal zero-crossing point as the time reference can construct a more accurate reconstructed signal.The basic principles of the method,simulation,and experimental comparison are also introduced.Based on the beam test platform of the Shanghai Synchrotron Radiation Facility(SSRF)and the method of experimental verification,the factors that affect the reconstructed signal quality are analyzed and discussed,including the depth of the sampled data,quantization noise of analog-to-digital converter,beam transverse oscillation,and longitudinal oscillation.The results of the beam experiments show that under the user operation conditions of the SSRF,a beam excitation signal with an amplitude uncertainty of 2%can be reconstructed.

Passive seismic velocity tomography on longwall mining panel based on simultaneous iterative reconstructive technique (SIRT)

Mining operation, especially underground coal mining, always has the remarkable risks of ground control. Passive seismic velocity tomography based on simultaneous iterative reconstructive technique （SIRT） inversion is used to deduce the stress redistribution around the longwall mining panel. The mining-induced microseismic events were recorded by mounting an array of receivers on the surface, above the active panel. After processing and filtering the seismic data, the three-dimensional tomography images of the p-wave velocity variations by SIRT passive seismic velocity tomography were provided. To display the velocity changes on coal seam level and subsequently to infer the stress redistribution, these three-dimensional tomograms into the coal seam level were sliced. In addition, the boundary element method （BEM） was used to simulate the stress redistribution. The results show that the inferred stresses from the passive seismic tomograms are conformed to numerical models and theoretical concept of the stress redistribution around the longwall panel. In velocity tomograms, the main zones of the stress redistribution arotmd the panel, including front and side abutment pressures, and gob stress are obvious and also the movement of stress zones along the face advancement is evident. Moreover, the effect of the advance rate of the face on the stress redistribution is demonstrated in tomography images. The research result proves that the SIRT passive seismic velocity tomography has an ultimate potential for monitoring the changes of stress redistribution around the longwall mining panel continuously and subsequently to improve safety of mining operations.

A new inversion method for reconstruction of plasmaspheric He^(+)density from EUV images

The Computer Tomography(CT)method is used for remote sensing the Earth’s plasmasphere.One challenge for image reconstruction is insufficient projection data,mainly caused by limited projection angles.In this study,we apply the Algebraic Reconstruction Technique(ART)and the minimization of the image Total Variation(TV)method,with a combination of priori knowledge of north–south symmetry,to reconstruct plasmaspheric He+density from simulated EUV images.The results demonstrate that incorporating priori assumption can be particularly useful when the projection data is insufficient.This method has good performance even with a projection angle of less than 150 degrees.The method of our study is expected to have applications in the Soft X-ray Imager(SXI)reconstruction for the Solar wind–Magnetosphere–Ionosphere Link Explorer(SMILE)mission.

2-D Conductor Cross Section Reconstruction via Amplitudes of Backscattered Field in Near Regions

In this paper, an improved approach is presented to reconstruct two dimensional conduc- tor profile illuminated by incident plane waves of multiple frequencies and directions via amplitudes of backscattered field in near regions. Newton-Kantorovitch algorithm is adopted to cast the non- linear coupled integral equations into linearized form, method of moment is used to transform the above linearized integral equations into matrix form, the resulting ill-posed overdetermined linear equations are solved using pseudoinverse technique based on Gram-Schedmit orthogonal procedure. Initial values are determined by solving a nonlinear least aquare error problem to establish an equivat lent circular cylinder. The effects of various parameters on reconstruction quality are discussed with numerical results and analysis.

基于超分辨率重建算法的二氧化碳浓度场研究

针对目前激光吸收光谱技术在非均匀分布烟道条件下获取CO_(2)初始信号进行浓度场重建时存在的计算时间长、重建精度低等问题,提出了一种基于超分辨率算法的CO_(2)浓度场重建方法,并对EO算法进行了优化改进。改进后的EO算法在CO_(2)浓度分布的计算中显著提升了迭代速度和搜寻精度;在超分辨率温度场重建算法方面,加入了输入补偿机制并优化了密集连接网络。经过实验对比验证,改进的CO_(2)浓度重建算法有效提高了重建精度,平均ARE与RMSE值分别达到了0.053733和0.054。

The Improved Simulated Annealing Algorithm and Application in the Surface Wave Dispersion Inversion

The velocity distribution of layers from surface wave dispersion curve is a severely nonlinear program. Base on the Metropolis rule,we improved the simulated annealing algorithm to simultaneously inverse the velocities and thicknesses using the dispersion data and identified the Moho and the bottom of lithosphere. The application to the numerical examples with 5% noise shows the velocity RMS is 1. 56% between the non-linear results and the original models when the condition of selecting method for temperature parameters and initial temperature are satisfied. Using the pure dispersions of Rayleigh wave,the nonlinear inversion has been carried out for S-wave velocities and thicknesses of the vertical profile crossing the Indian Plate,the Qinghai-Tibetan Plateau,and the Tarim Basin. It indicated that the crustal thickness is about 70 km in the Qiangtang block,while in the hinterland of the Qinghai-Tibetan Plateau the lithosphere is relatively thin(~ 130 km)from the velocity values and their offsets.

Radar Imaging Based on Iterative Algorithms

It has long been realized that the problem of radar imaging is a special case of image reconstruction in which the data are incomplete and noisy. In other fields, iterative reconstruction algorithms have been used successfully to improve the image quality. This paper studies the application of iterative algorithms in radar imaging. A discrete model is first derived, and the iterative algorithms are then adapted to radar imaging. Although such algorithms are usually time consuming, this paper shows that, if the algorithms are appropriately simplified, it is possible to realize them even in real time. The efficiency of iterative algorithms is shown through computer simulations.

ACCURATE ATTENUATION CORRECTION FOR ALGEBRAIC RECONSTRUCTION TECHNIQUE IN SPECT

We present a new iterative reconstruction algorithm to improve the algebraic reconstruction technique （ART） for the Single-Photon Emission Computed Tomography. Our method is a generalization of the Kaczmarz iterative algorithm for solving linear systems of equations and introduces exact and implicit attenuation correction derived from the attenuated Radon transform operator at each step of the algorithm. The performances of the presented algorithm have been tested upon various numerical experiments in presence of both strongly non-uniform attenuation and incomplete measurements data. We also tested the ability of our algorithm to handle moderate noisy data. Simulation studies demonstrate that the proposed method has a significant improvement in the quality of reconstructed images over ART. Moreover, convergence speed was improved and stability was established, facing noisy data, once we incorporate filtration procedure in our algorithm.

基于迭代重建算法的iDream重建技术对CT定量分析肺功能的影响研究

目的:探究不同iDream重建等级(1、3、5级)对CT定量分析肺功能参数的影响,为临床应用iDream重建技术定量测量肺气肿指标提供参考。方法:回顾性选取2021年12月至2022年1月在某院行胸部CT平扫的50例患者,分别使用滤波反投影(fittered back projection,FBP)、iDream 1级、iDream 3级、iDream 5级4种方法重建图像。测量4组图像的主气管CT值和标准差(standard deviation,SD)值并计算图像信噪比(signal to noise ratio,SNR),使用肺功能定量分析软件测量4组图像的双肺总容积(total lung volume,TLV)、肺气肿容积(emphysema volume,EV)、肺气肿指数(emphysema index,EI)、15%肺衰减值(15th percentile of lung attenuation,Perc 15)、15%肺质量(pulmonary density 15%,PD15%)。采用SPSS 22.0统计学软件进行数据对比。结果:4组间图像主气管CT值、TLV比较,差异无统计学意义(P>0.05),4组间SD、SNR、EV、EI、PD15%、Perc 15比较,差异有统计学意义(P<0.05)。随着iDream重建等级的增高,主气管SD值、EV、EI逐渐降低,iDream 3级组与iDream 5级组EV、EI比较,差异无统计学意义(P>0.05);随着iDream重建等级的增高,PD15%、Perc 15逐渐升高,iDream 3级组与iDream5级组PD15%、Perc 15比较,差异无统计学意义(P>0.05)。结论:随着iDream重建等级的增高可降低图像噪声,影响CT定量分析肺功能结果,iDream 3级和iDream 5级可保证EV、EI、PD15%、Perc 15相对稳定,不受迭代重建算法强度影响。

基于加窗随机解调架构的电网超谐波信号检测方法

针对电网超谐波检测采样压力大、数据处理困难等问题,提出一种基于加窗随机解调架构的超谐波信号检测方法。该方法首先利用模拟信息转换技术结合加窗思想,在采样端对超谐波信号进行加窗压缩采样,得到压缩采样后的数据;随后,在重构端采用逐级二分的思想,将残差的一阶微分作为收敛阈值,改进稀疏度自适应匹配追踪(SAMP)算法,实现对采样数据的快速重构。大量的仿真实验和测试结果表明,方法可以在减少90%数据量的情况下实现超谐波信号的频率幅值精确检测,其中频幅值检测的相对误差≤2%,频率检测误差≤3 Hz,为更准确测量超谐波提供了新思路。

AI技术在视频图像超清修复中的应用

随着时代的发展与进步,标清电视逐渐淡出大众视野。为顺应现代社会对于视频图像品质的追求,大量的标清经典影视作品面临着向高清分辨率的转换挑战,但是就转换结果来看,传统的标清在转换为高清后,图像的清晰度并没有得到显著提高。基于此,文章将以人工智能(Artificial Intelligence,AI)技术为核心,以经典标清影视作品1986年版《西游记》和1987年版《红楼梦》为例,结合超清的试验结果,对AI技术在视频图像超清修复中的应用效果进行深入分析。

基于光线重排的印制电路板高速扫描成像迭代去模糊方法研究

自动光学检测(automated optical inspection,AOI)相机运动速度过高,拍摄印制电路板(printed circuit board,PCB)图像会产生严重模糊。如能正确恢复因此而产生的退化,可提高相机的运动速度,进而提高AOI的检测效率。受代数迭代重建算法(algebraic reconstruction technique,ART)启发,提出一种基于光线重排的图像非盲去模糊算法。该方法在模糊核已知的情况下,基于快速迭代收缩阈值算法(fast iterative shrinkage thresholding algorithm,FISTA)迭代重建算法,运用Nestrov加速和光线重排提高了迭代收敛速度,运用数据正则抑制图像的各类加性噪声和伪影,较好地重建出原本的清晰图像。结果表明,该方法对噪声具有较好的抑制能力,对AOI相机运动曝光引起的严重模糊,较常用的传统逆滤波方法具有更好的图像恢复效果。

基于改进群稀疏正则化的稀疏角度图像重建

计算机断层扫描(Computer Tomography,CT)是临床医学中广泛使用的医学图像,可以清楚地显示人体的精细结构细节,为医生诊断疾病提供很大帮助。通过最近的研究表明,基于群稀疏正则化的联合代数重建技术(Simultaneous Algebraic Reconstruction Technique,SART)重建在稀疏角度采样背景下可以获得较好的性能。然而,群稀疏正则化在去掉伪影的同时,可能将边缘或细节过度平滑,使得对比度降低,无法获得符合人类视觉效果的高分辨率图像。因此,该文提出了一种基于改进群稀疏正则化的稀疏角度图像重建方法。首先对稀疏角度下的Shepp-Logan模型进行SART重建,再利用群稀疏正则化去除图像伪影,最后利用滚动引导滤波(Rolling Guided Filtering,RGF)进行对比度提升,再次作为SART的输入进行迭代。实验结果表明,该方法在视觉上以及PSNR(Peak Signal-to-Noise Ratio),MSE(Mean Squared Error)和FSIM(Feature Similarity)上均优于其他算法,并且在迭代初始阶段就具有较好的收敛性能。

基于多系统的GNSS三维水汽层析质量评价方法

本文基于提出的水汽层析廓线评价指标(tomographic profic fit score,TPFS),首次对GPS、北斗卫星导航系统(BeiDou Navigation Satellite System,BDS)、GLONASS和Galileo 4个系统的水汽层析结果进行了精度评估.结果表明:各GNSS水汽层析解算结果差异较小,最大均方根误差(root-mean-square error,RMSE)差距在11%之内,其中BDS水汽层析表现最好,GLONASS水汽层析表现最差.相较于GPS、GLONASS、Galileo,BDS在低层区域(2406 m以下)具有更好的层析解算优势.尤其在底层,BDS与GPS、GLONASS、Galileo的RMSE相比分别改进了3.2%、16.2%、5.2%.此外,在层析水汽廓线TPFS对比中,BDS平均TPFS最小;在暴雨天气下BDS水汽廓线TPFS最低,相较于GPS、GLONASS、Galileo改进了25.2%、31.5%、32.8%.

箱装废物γ核素的直接测量方法及验证

在获取γ放射性核素活度信息时,常规技术难以对放射性固体废物钢箱进行有效、全面分析,需利用非破坏性测量分析技术在钢箱处置前对其整体测量,国内目前尚无可对废物钢箱进行直接测量的方法及系统。本文通过对γ射线光谱测量分析算法的离散处理,结合传统CT原理,将放射性固体废物钢箱离散为2×5×3个体素,应用蒙特卡罗模拟结合代数重建技术建立了检测效率校准模型,完成了体素间串扰修正,解决了FA-Ⅳ型钢箱内γ放射性核素的直接测量问题,建立了相应的测量系统。为验证系统的可靠性,对钢箱内废物取样,送实验室进行γ射线光谱测量分析,并将两种方法的测量结果进行对比分析。结果显示,二者的相对偏差小于35%,验证了此系统的箱装废物直接测量方法可满足放射性固体废物钢箱测量分析和处置场废物接收数据测量误差在50%范围内的要求。

超低剂量CT联合高级建模迭代重建算法在成人肺结核检查中的可行性研究

目的:探讨超低剂量CT能谱纯化技术联合高级建模迭代重建(advanced modeling iterative reconstruction,ADMIRE)算法在成人肺结核检查中的可行性。方法:选取2022年5—12月某院收治的120例继发性肺结核(Ⅲ型)患者,按照随机数字表法将其分为A组、B组、C组、D组,每组30例。A组行常规剂量扫描,管电压为120 kV,管电流为110 mAs,采用滤波反投影重建算法;B组行低剂量扫描,管电压为120 kV,管电流为70 mAs,采用ADMIRE算法(3级);C组行低剂量扫描,管电压为100 kV,管电流为110 mAs,采用ADMIRE算法(3级);D组行超低剂量扫描,管电压为Sn100 kV,管电流为110 mAs,采用ADMIRE算法(3级)。比较4组患者的有效剂量(effective dose,ED)值、图像主观评分及客观评价指标等。采用SPSS 17.0统计学软件对数据进行处理。结果:4组患者的ED值、纵隔窗图像的主观评分、纵隔窗图像的信噪比及对比度噪声比比较,差异有统计学意义(P<0.05)。4组患者的肺窗图像主观评分、肺窗图像的信噪比及对比度噪声比比较,差异无统计学意义(P>0.05)。结论:超低剂量CT能谱纯化技术联合ADMIRE算法能够减少成人肺结核患者检查中的辐射剂量,同时图像质量能够满足临床诊断要求。

An ART iterative reconstruction algorithm for computed tomography of diffraction enhanced imaging

X-ray diffraction enhanced imaging （DEI） has extremely high sensitivity for weakly absorbing low- Z samples in medical and biological fields. In this paper, we propose an Algebra Reconstruction Technique （ART） iterative reconstruction algorithm for computed tomography of diffraction enhanced imaging （DEI-CT）. An Ordered Subsets （OS） technique is used to accelerate the ART reconstruction. Few-view reconstruction is also studied, and a partial differential equation （PDE） type filter which has the ability of edge-preserving and denoising is used to improve the image quality and eliminate the artifacts. The proposed algorithm is validated with both the numerical simulations and the experiment at the Beijing synchrotron radiation facility （BSRF）.