| 60Co Digital Radiography Imaging Systems series use the radioisotope 60Co as Ray-source and the gas-pressurized array ion-chamber, which possesses multinational patents, as detector to acquire signals. The series include not only the Train Cargo Inspection System, which can inspect train cargo on-line, but also the Large Container CT Inspection System (LCCT), which can reconstruct the three-dimensional images of containers or missiles. This paper will test the precision of LCCT's Material quality determination, analyze the causations reducing the precision and design the scheme of scatter correction.After introducing CT's evolution, classification, theory, image reconstruction algorithms and evaluation criterions, this paper described the structure of LCCT and demonstrated its characteristics and performance through real images.Then, LCCT's material quality determination was studied thoroughly. Theoretically, the results of CT represent the substance and density of being-detected objects. Careful tests proved that LCCT can differentiate two waters with the density distinction of 1 percent. Meanwhile, some errors were discovered lowering this system's precision. We classified these errors into several kinds and respectively analyzed what cause them. As a result, scatter of 7 photons is an important causation.The last part is correction of scatter. Firstly, I listed the common methods of scatter correction and their effect, limiting factors and applicable situation. Among them, considering LCCT's present conditions, developing an algorithm including the scatter model is the most appropriate. In order for this method to work effectively, the model is the key. We should establish a scatter model not only accordant to LCCT's real physical process but also simplified for not bringing burden of calculation. The ideal model is concluded and the simplification directions and ways are discussed at last.
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