title: Iterative image reconstruction using modified non-local means filtering for limited-angle computed tomography.
abstract: OBJECTIVE
  Limited-angle CT imaging is an effective technique to reduce radiation. However, existing image reconstruction methods can effectively reduce streak artifacts but fail to suppress those artifacts around edges due to incomplete projection data. Thus, a modified NLM (mNLM) based reconstruction method is proposed.
  
  
  METHODS
  Since the artifacts around edges mainly exist in local position, it is possible to restore the true pixels in artifacts using pixels located in artifacts-free regions. In each iteration, mNLM is performed on image reconstructed by ART followed by positivity constraint. To solve the problem caused by ART-mNLM that there is undesirable information that may appear in the image, ART-TV is then utilized in the following iterative process after ART-mNLM iterates for a number of iterations. The proposed algorithm is named as ART-mNLM/TV.
  
  
  RESULTS
  Simulation experiments are performed to validate the feasibility of algorithm. When the scanning range is [0, 150°], our algorithm outperforms the ART-NLM and ART-TV with more than 40% and 29% improvement in terms of SNR and with more than 58% and 49% reduction in terms of MAE. Consistently, reconstructed images from real projection data also demonstrate the effectiveness of presented algorithm.
  
  
  CONCLUSIONS
  This paper uses mNLM which benefits from redundancy of information across the whole image, to recover the true value of pixels in artifacts region by utilizing pixels from artifact-free regions, and artifacts around the edges can be mitigated effectively. Experiments show that the proposed ART-mNLM/TV is able to achieve better performances compared to traditional methods.
authors: Department of Biomedical Engineering, Southern Medical University, Guangzhou 510515, China.
authors: Hongliang
authors: H
authors: Qi
authors: Department of Biomedical Engineering, Southern Medical University, Guangzhou 510515, China.
authors: Zijia
authors: Z
authors: Chen
authors: Department of Biomedical Engineering, Southern Medical University, Guangzhou 510515, China.
authors: Shuyu
authors: S
authors: Wu
authors: Department of Biomedical Engineering, Southern Medical University, Guangzhou 510515, China. Electronic address: yuanxu@smu.edu.cn.
authors: Yuan
authors: Y
authors: Xu
authors: Department of Biomedical Engineering, Southern Medical University, Guangzhou 510515, China. Electronic address: smart@smu.edu.cn.
authors: Linghong
authors: L
authors: Zhou
mesh_terms: D000465:Algorithms; D016477:Artifacts; D003198:Computer Simulation; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D015233:Models, Statistical; D019047:Phantoms, Imaging; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D059629:Signal-To-Noise Ratio; D014057:Tomography, X-Ray Computed
keywords: Artifacts nearby edges; Computed tomography; Image reconstruction; Limited-angle projection; Non-local means filtering