联合代数重建算法中基于像素的投影计算方法

联合代数重建法是CT重建的一种重要方法,算法中投影计算时间占重建时间的一半以上。提出一种可以在联合代数重建方法中快速计算投影系数矩阵并优化内存的方法。该方法从每个像素出发直接定位到相交射线,随后利用该结果完成投影系数的计算．并可利用射线、像素的相关性优化计算。     

松弛系数-有序子集-最大似然期望算法在60Co集装箱CT检测中的应用

将松弛系数和迭代间像素值约束引入有序子集一最大似然期望算法中,构造出应用于发射CT中的ROSEM算法引入到透射式工业CT中。不仅加快了图像重建的收敛速度而且改善了重建图像的质量。针对ROSEM、代数迭代算法（ART）和卷积反投影算法（CBP）,分别做了模拟实验和实际汽车CT检测以及集装箱CT检测实验,并分析比较了它们在^60Co集装箱CT检测中的应用。ROSEM算法无论在重建速度还是重建质量上都优于ART算法,其重建图像质量和CBP算法相当。     

代数迭代算法进行CT图像重建的研究

对CT代数迭代重建算法(ART)进行了研究,讨论了射线数目对图像重建效果的影响,并采用平滑方法,改善了重建图像质量,加快了收敛速度,得出了效果满意的工业CT图像。     

板状物成像方法研究

在工业CT成像应用中,板状物结构件受形状、结构、组分等特征的限制,使得射线能量与有效厚度不匹配,常规的扫描方式易使投影数据缺失,投影数据完备性较差。为此,讨论了一种基于倾斜圆扫描轨迹和代数迭代重建技术的CT成像模式。首先,在倾斜圆轨迹的基础上进行投影几何关系建模,结合空间几何知识完成投影矩阵的刻画;其次,基于迭代重建算法对轨迹的无约束化,研究任意扫描轨迹的迭代重建算法;最后通过板状物成像仿真实验,验证了算法的正确性和可行性。对于板状物结构件,该方法相对于传统的圆轨迹扫描,投影数据更完备,CT重建质量高。     

一种地面放射性污染分布重建算法的研究北大核心CSCD

提出了一种基于低空测量数据的地面放射性污染分布重建算法,该算法可以应用在"脏弹"爆炸后放射性污染分布重建计算中。该算法通过求解探测器响应系数方程组进而重建出地面污染分布,研究显示该算法在探测高度小于50 m时能比较好地重建地面放射性污染的分布。     

一种地面放射性污染分布重建算法的研究

提出了一种基于低空测量数据的地面放射性污染分布重建算法,该算法可以应用在"脏弹"爆炸后放射性污染分布重建计算中。该算法通过求解探测器响应系数方程组进而重建出地面污染分布,研究显示该算法在探测高度小于50 m时能比较好地重建地面放射性污染的分布。     

X射线非完整扫描情况下的缺陷检测研究

CT技术是一种先进的无损检测手段,被广泛应用于医学和工业领域.针对大型工业构件的无损检测问题,提出了一种x射线非完整扫描情况下的缺陷检测方法.在构件使用之前预先采集一套原始的非完整扫描投影数据,采用代数重建算法进行图像重建,将重建图像作为基准图像.再采集构件使用之后不同时刻的非完整扫描投影数据,将其重建图像与基准图像进...     

基于模拟点源测量的多针孔SPECT精确迭代重建

高分辨率单光子发射计算机断层成像（SPECT）是临床和小动物影像的重要技术之一。对SPECT的系统传输矩阵进行建模,并结合于迭代重建算法中,是提高系统空间分辨率的有效手段。本文基于实验室自主研发的多针孔小动物SPECT系统,研究了一种蒙特卡罗模拟和解析模型相结合的系统传输矩阵精确计算方法。该方法是基于多点源模拟的投影数据,结合数据再估计方法和高斯拟合方法提取点扩展函数（PSF）特征参数,并结合解析形式的系统物理模型,从而计算任意位置的精确PSF。通过对四点源模拟投影数据分别用纯解析方法和蒙特卡罗模拟与解析模型相结合的方法进行计算,并对所得的系统传输矩阵进行重建对比,验证了蒙特卡罗模拟与解析模型相结合方法对图像分辨率的改善效果。进一步比较了不同点源排列的重建效果,获得了优化的点源排布方案。相对于基于实验方法测量系统传输矩阵,本方法能以更合理的代价实现系统传输矩阵的精确建模,并能有效提高系统空间分辨率。     

体素投影分类ART算法快速重建CT图像

为克服CT图像重建中代数重建算法(ART)不足,基于体素投影分类的方法,提出了一种快速计算加权因子的策略,进而提出了重建CT图像的快速ART算法。相比于常用Siddon方法计算加权因子的ART算法,虽然该算法的重建精度略逊,但是解决了原ART算法计算非常费时和所需存储空间大的问题。仿真实验结果证明了该算法的有效性。     

基于图像旋转全变分约束迭代重建算法

为解决传统全变分最小化图像重建算法中因系统矩阵运算而导致的重建速度慢、内存开销大的问题,本课题提出一种图像旋转全变分算法。算法以自适应最速下降-投影到凸集算法为基础,利用插值算法实现图像旋转并进行重建。实验结果表明,相较于经典ASD-POCS算法,该算法能在保持重建精度的情况下,使重建速度提高将近6倍,并大大减少内存开销。     

Computation and stability analysis for regularized tomographicreconstructions

Deals mainly with the assessment of the stability of various reconstruction methods for computed tomography. The authors also present the convex dual formulation of the optimization problems in entropy-like methods. For each of these methods, the influence of errors in the measured data on the reconstructed image is analyzed. A small perturbation of the data vector induces a perturbation of the reconstructed image which can be computed by means of the sensitivity matrix. Using appropriate matrix computation techniques, an upper bound on the size of the reconstruction error is determined, as well as the pattern of noise in the sinogram that will result in the largest reconstruction error and the standard deviation map in the reconstructed image domain. Simulations illustrate the authors' analysis and demonstrate its utility in the interpretation of computed images and in the selection of reconstruction parameters     

3D image reconstruction for a Compton SPECT camera model

Proposes a 3D image reconstruction algorithm for a 3D Compton camera being developed at the University of Michigan. The authors present a mathematical model of the transition matrix of the camera which exploits symmetries by using an adapted spatial sampling pattern in the object domain. For each projection angle, the sampling pattern is uniform over a set of equispaced nested hemispheres. By using this sampling pattern the system matrix is reduced to a product of a (approximately) block circulant matrix and a sparse interpolation matrix. This representation reduces the very high storage and computation requirement inherent to 3D reconstruction using transition matrix inversion methods. The authors geometrically optimize their hemispherical sampling and propose a 3D volumetric interpolation. Finally, the authors present a 3D image reconstruction method which uses the Gauss-Seidel algorithm to minimize a penalized least square objective     

High-speed computation of the EM algorithm for PET imagereconstruction

The PET image reconstruction based on the EM algorithm has several attractive advantages over the conventional convolution backprojection algorithms. However, two major drawbacks have impeded the routine use of the EM algorithm, namely, the long computational time due to slow convergence and the large memory required for the storage of the image, projection data and the probability matrix. Here, the authors attempt to solve these two problems by parallelizing the EM algorithm on a multiprocessor system. They have implemented an extended hypercube (EH) architecture for the high-speed computation of the EM algorithm using the commercially available fast floating point digital signal processor (DSP) chips as the processing elements (PEs). The authors discuss and compare the performance of the EM algorithm on a 386/387 machine, CD 4360 mainframe, and on the EH system. The results show that the computational speed performance of an EH(3,1) using DSP chips as PEs executing the EM image reconstruction algorithm is about 130 times better than that of the CD 4360 mainframe. The EH topology is expandable with more number of PEs     

矩阵分裂算法在两相流方程求解中的应用初步研究

矩阵分裂算法是一种有限差分方法,根据系统特征值的正负,确定对流项差分格式,能描述流场信息传播的真正方向。本文基于隐式矩阵分裂算法对两相流均相流模型进行离散,利用矩阵形式追赶法求解离散后的块三对角矩阵,运用FORTRAN90程序实现数值求解过程。运用喷管内流动和两相可压缩性实验两个基准题对算法进行校验,计算结果和解析结果吻合良好,证明求解方法的可靠性。本文成功运用矩阵分裂算法求解两相流模型,为热工水力计算程序的开发和改进提供了新的视角。     

数字图象重建的一种综合快速算法

本文提出一种综合快速算法,可直接快速地计算重建图象平面上任何一点的检测角,并采用三次B样条函数对滤波的投影数据进行内插,来代替反投影时的内插。实验表明,在保证同样的主客观保真度下,此算法的内插计算量约为原来算法的1/12;当象素数N增大时,计算量的减少更为显著。对端点条件的影响进行了分析,证明用此法插值所造成的误差以相当高的速率由边缘向中心衰减,大约每向中心移动两个象素其误差减少一个数量级。     

Acceleration optimization of real-time equilibrium reconstruction for HL-2A tokamak discharge control

Real-time equilibrium reconstruction is crucially important for plasma shape control in the process of tokamak plasma discharge.However,as the reconstruction algorithm is computationally intensive,it is very difficult to improve its accuracy and reduce the computation time,and some optimizations need to be done.This article describes the three most important aspects of this optimization:(1) compiler optimization;(2) some optimization for middle-scale matrix multiplication on the graphic processing unit and an algorithm which can solve the block tri-diagonal linear system efficiently in parallel;(3) a new algorithm to locate the XO point on the central processing unit.A static test proves the correctness and a dynamic test proves the feasibility of using the new code for real-time reconstruction with 129?×?129 grids;it can complete one iteration around 575 μs for each equilibrium reconstruction.The plasma displacements from real-time equilibrium reconstruction are compared with the experimental measurements,and the calculated results are consistent with the measured ones,which can be used as a reference for the real-time control of HL-2 A discharge.     

Algorithms for Fast Back- and Re-Projection in Computed Tomography

While the computation time for reconstructing images in C.T. is not a problem in commercial systems, there are many experimental and developmental applications where resources are limited and image reconstruction places a heavy burden on the computer system. This paper describes a very efficient back-projection algorithm which results in large time savings when implemented in machine code. Also described is a minor modification to this algorithm which converts it to a re-projection procedure with comparable efficiency.     

用多个能量探测方法校正层析γ扫描透射图像重建中射线线衰减系数

对采用多个能量探测方法来校正层析γ扫描透射图像重建中射线线衰减系数进行了初步探讨.应用蒙特卡洛方法计算了18种材料在不同能量下的γ射线线衰减系数,并拟合得出当物质材料和密度确定时γ射线的线衰减系数与能量的关系,从而重建出不同能量下的透射图像.     

R-L Method and BLS-GSM Denoising for Penumbra Image Reconstruction

When neutron yield is very low, reconstruction of coding penumbra image is rather difficult. In this paper, low-yield （109） 14 MeV neutron penumbra imaging was simulated by Monte Carlo method. The Richardson Lucy （R-L） iteration method was proposed to incorporated with Bayesian least square-Gaussian scale mixture model （BLS-GSM） wavelet denoising for the simulated image. Optimal number of R-L iterations was gotten by a large number of tests. The results show that compared with Wiener method and median filter denoising, this method is better in restraining background noise, the correlation coefficient Rsr between the reconstructed and the real images is larger, and the reconstruction result is better.