Study On Iterative Reconstruction Algorithm Of Transmission Tomographic Gamma Scanning

With the rapid development of nuclear industry,a large number of nuclear waste will inevitably be produced.As one of the most advanced non-destructive assays for nuclear wastes,tomographic Gamma Scanning?TGS?is able to give accurate quantitative and qualitative measurements of nuclear waste drums.The transmission reconstruction,as an essential component in TGS,provides attenuation corrections for the following emission reconstruction,and contributes to accurate nuclear waste analysis.So how to improve the accuracy of transmission reconstruction is an important access of improving TGS technique.This paper studies on the initial value picking-up technique in traditional iterative algorithm.To improve the accuracy of TGS transmission reconstruction.,3non-iterative optimization methods:Non-minimization optimization?NMO?,back projection technique?BPT?and Tikhonov regularization algorithm are used in this paper,to optimize initial values in traditional iterative algorithm:maximum likelihood expectation maximization?MLEM?by solving transmission TGS equation.Based on this,3 initial value optimization methods:NMO-MLEM,BPT-MLEM and Tikhonov-MLEM are proposed.Both simulation and real experiment of TGS transmission scanning are conducted in this paper for verification.Firstly,by using monte-carlo computation program:MCNP,the simulation of transmission scanning measurement with one-layer heterogeneous sample?5×5 voxels?and transmission source:⁶⁰Co and¹³⁷Cs is conducted.Reconstruction results show that reconstructed values of 3 improved methods are consistent with reference values,which proves the applicability of initial value optimization technique in transmission TGS;and by comparing with MLEM?reconstruction error range:5.52%²3.90%?,3 proposed methods are able to improve the accuracy of reconstruction?BPT-MLEM error range:3.27%²0.56%,Tikhonov-MLEM error range:0.57%¹7.28%,NMO-MLEM error range:1.97%¹0.78%?;for 3 initial value optimization technique studied in this paper,NMO has the best optimization performance,BPT has relatively the worst performance.Transmission scanning experiments based on transmission source:¹⁵²Eu and one-layer sample filled with 7 heterogeneous materials are carried out.All 3 improved methods and traditional MLEM are used for reconstruction,and image Image evaluation parameters:normalized root mean square error?NRMSE?and correlation coefficient?CC?are introduced for optimization performance evaluation.Reconstruction results show that the accuracy of reconstruction is proportional to the transmitted energy.Compared with the traditional MLEM,3 improved algorithms can effectively reduce the artifacts and improve the quality of reconstructed transmission images.And for 3 optimization methods studied in this paper,optimization performance:NMO>Tikhonov>BPT.This study shows that initial value optimization technique is applicable to TGS transmission reconstruction,and can effectively improve the accuracy of transmission image reconstruction,which provides new access and verification of accurate,stable image reconstruction in TGS transmission technique.