Anisotropic total variation minimization approach in in-line phase-contrast tomography and its application to correction of ring artifacts

In-line phase-contrast computed tomography(IL-PC-CT) imaging is a new physical and biochemical imaging method.IL-PC-CT has advantages compared to absorption CT when imaging soft tissues. In practical applications, ring artifacts which will reduce the image quality are commonly encountered in IL-PC-CT, and numerous correction methods exist to either pre-process the sinogram or post-process the reconstructed image. In this study, we develop an IL-PC-CT reconstruction method based on anisotropic total variation(TV) minimization. Using this method, the ring artifacts are corrected during the reconstruction process. This method is compared with two methods: a sinogram preprocessing correction technique based on wavelet-FFT filter and a reconstruction method based on isotropic TV. The correction results show that the proposed method can reduce visible ring artifacts while preserving the liver section details for real liver section synchrotron data.     

计算机统一设备架构加速外部计算机断层图像重建

外部计算机断层成像(CT)重建主要用于重建管状物(如管道)的管壁截面图像,具有重要的实际意义。外部CT重建算法中,带子区域平均图像总变差最小的凸集投影(SA-TVM-POCS)重建数值算法可以得到高质量的CT图像,可用于管道的无损检测。但由于在实现过程中计算量较大,阻碍了其在一些时间要求较高环境中的应用。计算机统一设备架构(Computer Unified Device Architecture, CUDA)是近几年发展起来的解决高强度计算的有效工具之一,该文利用CUDA的高强度并行计算性能,提高外部CT问题SA-TVM-POCS算法的速度,从而增加该算法的应用范围;为充分利用CUDA其高强度数据级并行计算能力,该文改进了SA-TVM-POCS算法的实现过程以适应CUDA的并行计算架构。实验结果表明,该文方法可以在重建图像质量没有下降的情况下,加速比达到20倍以上;所以,利用CUDA可以加快SA-TVM-POCS算法的计算速度。     

PET image reconstruction with a system matrix containing point spread function derived from single photon incidence response

A point spread function(PSF)for the blurring component in positron emission tomography(PET)is studied.The PSF matrix is derived from the single photon incidence response function.A statistical iterative reconstruction(IR)method based on the system matrix containing the PSF is developed.More specifically,the gamma photon incidence upon a crystal array is simulated by Monte Carlo(MC)simulation,and then the single photon incidence response functions are calculated.Subsequently,the single photon incidence response functions are used to compute the coincidence blurring factor according to the physical process of PET coincidence detection.Through weighting the ordinary system matrix response by the coincidence blurring factors,the IR system matrix containing the PSF is finally established.By using this system matrix,the image is reconstructed by an ordered subset expectation maximization(OSEM)algorithm.The experimental results show that the proposed system matrix can substantially improve the image radial resolution,contrast,and noise property.Furthermore,the simulated single gamma-ray incidence response function depends only on the crystal configuration,so the method could be extended to any PET scanner with the same detector crystal configuration.