Research On Fast Image Reconstruct With ART Algorithm Based On DDM Projection Method

Digital technology plays a key role in the field of cultural relic conservation.3D laser scanning is mainly used in the traditional digital technology to model the surface of cultural relics.However,the internal structure,material and defect information of cultural relics can not be obtained by this kind of technology.Computed Tomography(CT)has been gradually adopted in the field of digital preservation of cultural relics due to its high accuracy and nondestructive detection of the internal structure of objects.Reconstructionalgorithm is the core of CT technology,as a typical iterative algorithm,the accuracy and speed of Algebraic Reconstruction Techniques(ART)are directly affected by the calculation method of projection coefficient.As an advanced projection coefficient calculation method,DDM algorithm uses the method of mapping pixels and detectors on the projection axis to calculate the weight factor and obtain good reconstruction quality.However,the DDM algorithm has a large amount of calculation and a slow calculation speed.In this paper,the improved projection calculation method and multi-thread parallel acceleration are used to implement the ART algorithm fast image reconstruction which is based on DDM projection algorithm.The main work of the paper is as follows:(1)Aiming at the problem of slow calculation speed of ART algorithm in fan beam CT system,a 2D DDM fast projection algorithm is proposed.Firstly,the ray in the DDM model is split.Because the distance increment of the ray through the fixed step length remains unchanged,the position relationship between the distance increment and the pixel is used to infer the ray passing through the boundary of the following pixels.The pixel index is directly recursively obtained and the intersection coordinates are updated to quickly calculate the weight factor.The results show that this method can increase the reconstruction speed of ART algorithm by about 1.7 times on the premise of ensuring the correct calculation,and it achieves 2.1 times speedup compared with the traditional DDM algorithm in projection calculation.(2)Aiming at the slow computing speed of ART algorithm in conical beam CT system,a fast 3D DDM projection algorithm is proposed.Extending the 2D to 3D,determined according to the slope of the cone beam projection plane,boundary are obtained by the cone beam split ray distance increment relation with the location of the voxel,recursion is a layer of voxel projection plane up and down and boundary ray intersection situation,quickly calculate the area of the projection plane overlapping rectangles,can quickly get the weight factor and voxel index.The results show that under the premise of constant reconstruction accuracy,the ART algorithm based on this algorithm achieves 1.6 times of acceleration ratio in overall reconstruction and 3 times of acceleration ratio in projection calculation compared with the ART algorithm based on traditional DDM algorithm.(3)In order to improve the reconstruction speed of ART algorithm under conical beam,a parallel multi-thread ART reconstruction algorithm based on fast DDM projection under3 D conical beam is proposed.By using the p Threads multi-thread parallel programming technology,the task is split in line with the ray range of the detector plane,so that the most time-consuming projection calculation part of the ART algorithm is executed in parallel,and the overall reconstruction speed is improved.Aiming at the load balancing problem,the parallel algorithm is optimized by further dividing tasks according to the total rays passing through the object to be measured.The results show that compared with the serial ART algorithm based on fast DDM algorithm,the acceleration ratio of the whole reconstruction in the six-core parallel algorithm is 4.8 times,and compared with the serial ART algorithm based on original DDM projection algorithm,the acceleration ratio of the whole reconstruction in the six-core parallel algorithm is about 8 times.