| In the practical CT applications, because of mechanical design and abrasion, the position of scanning lamp-house and the detector must have errors. So in the course of the emendation, it is necessary to consider the two errors on the CT system.The purpose of this article is to find the artifacts'rules in the reconstruction images, and at the same time controls the disturbance in some degree so as to make the change of the spatial resolution in a small bound. The experiment has three steps. First, the experiment adopts a series of balls whose radius is 2mm as the phantom to observe the artifacts. The results indicate that in situation of the elliptical orbit scanning, the reconstruction images appear tailing phenomenon, modulation of the cosine function causing the boundary divergence in the reconstruction images and the detector tilting shows the annular artifacts in the images. Secondly, we adopt the bead whose radius is 0.6mm as the phantom to observe the reconstruction results by the methods of point-object imaging. The results show that as the disturbance increasing bead's shape changes and the blurring become strong. At last, method of edge-object imaging and edge-derivative are applied to calculate the PSF value, whose phantom is the ball of radius 1.2mm. Comparing to the PSF value we find that detector tilting has the most impact on the spatial resolution in the system, the least is the cosine modulation.The experiment indicate that artifacts of the reconstruction images have their rules, who are great helpful for the correction work. Comparing to the PSF value in the different disturbance situation, we can control the disturbance in some degree; For the calculation of PSF, we study the calculation of the 3D PSF on the base of the 2D situation; In theory, method of edge-derivative is very easy and its precision is high comparatively. It is suitable for the large data calculation. So the application of this article is very wider. |
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