Iterative Algorithm For Cone-beam Spiral Ct

Computed Tomography (CT) is a technology with which we can know the structure of an object in the way of non-destruction. Up to now it has been used widely in fields of such as medical diagnosis, nondestructive examination, and aeronautics and astronautics etc.Cone-beam CT has much advantage over 2D parallel-beam and fan-beam CT in the aspects of speed in obtaining data, spatial resolution and the utilization ratio of rays. Now CT in commerce are turning to using cone-beam CT. Helical cone-beam CT, the cone-beam CT with helical scanning path, has been known for using less X-rays, scanning fast with large volume, high accuracy of reconstruction. So it has become a hot topic in the field of CT image reconstruction.At present the research on reconstruction algorithms of helical cone-beam CT is generally based on analytic algorithms, and these methods usually need complete projection data. In practice complete projection data cannot be obtained out of objective cause, so analytic methods fail in this case. Iterative algorithms have gotten more and more attention for it can reconstruct images simply and effectively and can reconstruct images with incomplete projection data. Some exploratory study has been issued on helical cone-beam in this paper. The main context is as follows:Firstly, a fast and real-time method of obtaining projection matrix is proposed according to the characteristic of helical cone-beam CT. The analysis on complexity is done. The effectiveness of proposed algorithms is proved by some experiments.Secondly, the effect of pitch on reconstructed result is gotten through reconstructing images with projection data in different pitches. The experimental results show that the pitch can usually be chosen as 0.5-1.5 times the height of detector on the condition that cone-beam effect is not obvious. Thus the reconstructed speed can be fastened, the amount of radiation can be reduced, and better reconstructed results can be obtained.Lastly, the iterative algorithms are done with the projection data in case of sparse and sight-limited. The experimental results show that better images can still be gotten by using iterative reconstruction algorithm with incomplete projection data. On the condition that the amount of projection is fixed we can get better results with sparse projection data than sight-limited. But with loss of the projection data, the quality of reconstruction will get worse, and the artifacts become more serious.The arrangement of research context can know how the value of pitch and projection angle influences the reconstruction image. With this better images can be gotten.