高密度差多层球壳双能CT图像重建方法

Image reconstruction method of dual energy CT for multilayer spherical shell with great density difference

对含高密度差材料的大尺寸多层球壳构件采用双能CT方法进行无损检测,当采用高能射线扫描时,低Z材料区对射线基本无阻挡,而采用低能射线扫描时又会被高Z材料区截断,因此需要根据双能射线投影特征开展针对性的图像重建方法研究。首先,根据材料结构特征建立仿真模型,分别模拟得到高、低能射线的投影正弦图,然后采用滤波反投影和代数重建法等算法进行图像重建。通过仿真和比较分析,得出先融合投影再重建图像的方法要整体优于先分别重建再融合图像的方法。另外,为保证图像重建质量,在进行扫描射线能量选择时,要考虑提高局部投影质量,更要尽量减少被截断的总投影量。

The dual energy CT method can be used in nondestructive test for large size multilayer spherical shell with high density difference materials.LowZ materials basically have no barrier to high energy X-ray scanning,while low energy scanning will be truncated by high Z materials,hence image reconstruction methods need to be studied according to the dual energy X-ray projection features.The simulation model is designed according to the structure characteristics of the multilayer spherical shell,and projection sonograms for both high and low energy X-rays are simulated respectively,on this basis,images are reconstructed with Filtered Back Projection（FBP）or Algebraic Reconstruction Technique（ART）algorithm.Through a mass of simulation and comparative analysis,the conclusion is drawn that the F-R（fuse first and then reconstruct）method is better than the R-F（reconstruct first and then fuse）method for image reconstruction of the dual energy CT.It is pointed out that in order to ensure the image reconstruction quality,for the scanning X-ray energy choice,it is necessary not only to improve local projection quality,but also to minimize the total amount of the truncated projection.