The basic principle of industrial CT is based on the attenuation and absorption characteristics of radiation in the detected object. It is related to the absorption ability of matter to radiation and the nature of matter. Therefore, the attenuation rule and distribution of X-rays or gamma; rays with certain energy and intensity emitted by radionuclides or other radiation sources in the detected object may be displayed by the detector to obtain the detailed information of the object interior. Finally, the computer information processing and image reconstruction technology can be used to display them in the form of images.    

　　Compared with the conventional nondestructive testing methods, industrial CT testing has the advantages of accurate positioning, easier image recognition, higher density resolution, high dynamic response range, etc. the gray scale of image corresponds to the material, geometric structure, component and density characteristics of workpiece, which can not only obtain the shape, position and size of defects, but also determine the nature of defects by combining the density analysis technology Quality, which has puzzled NDT personnel for a long time, has a more direct way to solve the problems of defect space positioning, depth quantitative and comprehensive qualitative.