Study On CT Reconstruction Algorithm Based On A Sort Of Scanning With Oblique Incidence

Industrial piece with large and flat size is widely used in industrial production. Its geometric feature is that its width and length can reach from a few meters to even several decadal meters. However, its thickness is only from a few centimeter to several decadal centimeter. As a result, CT reconstruction directed toward industrial piece with large and flat size has great practical importance.Because the thickness or height of the industrial piece with large and flat size is far smaller than the size of the other two directions, it is impossible to obtain the complete projecting data when the industrial piece with large and flat size is scanned by using normal projecting manner. For industrial piece with large and flat size, the normal CT detecting method is not available. So in this article a kind of method which is called unconventional CT technology is presented. That means the rake anglebetween main beam which comes from radiographic source and rotation axis of the object is not 90(.Meanwhile, The plane array detector is vertical to the rotation axis of the object. When detecting, the detected piece and the plane array detector is stationary. The two-dimension projecting data of the detected piece is obtained when the radiographic source rotate around the rotation axis. Then the three-dimension reconstruction algorithm is explored according to the two-dimension projecting data above.The research is concentrated on the filter back-projection reconstruction algorithm using unconventional CT scanning manner and studying the implementation procedure of the above reconstruction algorithm based on computer simulation. The projection algorithm of parallel beam and conical beam which is based on ellipsoid and cylinder projection algorithm under the condition of unconventional scanning is studied. Then the calculating formula of back-projection address is obtained under such scanning mode. Following the unconventional CT filter back-projection algorithm in the mode of computer simulating is realized. In the process of realizing algorithm, the problem-solving methods of the following questions, such as the selection of incidence, interpolation and decomposition, discretization or selection of the convolutional function are presented. Meanwhile, the results of directly weighted back-projection reconstruction algorithm are compared with that of the filter back-projection reconstruction algorithm both under the incident condition of parallel beam and conical beam. Finally, the effect of different filter, incident angle and projection number on reconstruction result are analyzed.