Few-view CT reconstruction via a novel non-local means algorithm.
OBJECTIVE
Non-local means (NLM) based reconstruction method is a promising algorithm for few-view computed tomography (CT) reconstruction, but often suffers from over-smoothed image edges. To address this problem, an adaptive NLM reconstruction method based on rotational invariance (ART-RIANLM) is proposed.


METHODS
The method consists of four steps: 1) Initializing parameters; 2) ART reconstruction using raw data; 3) Positivity constraint of the reconstructed image; 4) Image updating by RIANLM filtering. In RIANLM, two kinds of rotational invariance measures which are average gradient (AG) and region homogeneity (RH) are proposed to calculate the distance between two patches and a novel NLM filter is developed to avoid over-smoothed image. Moreover, the parameter h in RIANLM which controls the decay of the weights is adaptive to avoid over-smoothness, while it is constant in NLM during the whole reconstruction process. The proposed method is validated on two digital phantoms and real projection data.


RESULTS
In our experiments, the searching neighborhood size is set as 15×15 and the similarity window is set as 3×3. For the simulated case of Shepp-Logan phantom, ART-RIANLM produces higher SNR (36.23dB>24.00dB) and lower MAE (0.0006<0.0024) reconstructed images than ART-NLM. The visual inspection demonstrated that the proposed method could suppress artifacts or noises more effectively and recover image edges better. The result of real data case is also consistent with the simulation result.


CONCLUSIONS
A RIANLM based reconstruction method for few-view CT is presented. Compared to the traditional ART-NLM method, SNR and MAE from ART-RIANLM increases 51% and decreases 75%, respectively.
Department of Biomedical Engineering, Southern Medical University, 510515 Guangzhou, China.
Zijia
Z
Chen
Department of Biomedical Engineering, Southern Medical University, 510515 Guangzhou, China.
Hongliang
H
Qi
Department of Biomedical Engineering, Southern Medical University, 510515 Guangzhou, China.
Shuyu
S
Wu
Department of Biomedical Engineering, Southern Medical University, 510515 Guangzhou, China. Electronic address: yuanxu@smu.edu.cn.
Yuan
Y
Xu
Department of Biomedical Engineering, Southern Medical University, 510515 Guangzhou, China. Electronic address: smart@smu.edu.cn.
Linghong
L
Zhou
D000465:Algorithms; D016477:Artifacts; D055592:Biophysical Phenomena; D003198:Computer Simulation; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D015233:Models, Statistical; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D059629:Signal-To-Noise Ratio; D014057:Tomography, X-Ray Computed / Q000009:adverse effects / Q000379:methods* / Q000706:statistics & numerical data*
CT reconstruction; Few projections; Non-local means; Rotational invariance