| Computer tomography(CT)can uses the X-ray attenuation values from different view angles to reconstruct the internal structural information of object.It can destructive,accurate and intuitive demonstrate the internal structural information.Among all of the CT,because of its flexible and low radiation dose,cone-beam CT scan mode has been widely used in medical examination and local tissue imaging.In order to decrease hardware costs of cone-beam CT,reduce radiation dose,increase the field of view and eliminate the artifacts because of the incomplete data,this thesis introduces an offset cone-beam CT system.It expand the field of view by moving the detector,which reduces the radiation dose,and doesn’t increase the mechanism complexity.As a result of the special system structure,the data of projection is not complete,and we cannot directly use the conventional reconstruction algorithm for image reconstruction.Based on the basic CT theory and reconstruction algorithm,this thesis performs detailed analysis and rigorous mathematical derivation on Interpolation rearrangement offset reconstruction algorithm and Pre-weighted offset reconstruction algorithm.Interpolation rearrangement offset reconstruction algorithm is complicated,and it would lead to the reduction of spatial resolution and degradation of image quality.Because of these many shortcomings,it has been excluded from alternatives.Pre-weighted offset reconstruction algorithm takes advantage of data redundancy.The redundant area data were weighted to ensure that projection data were smooth and their sum in back projection is only one.This not only avoids the increase of computational complexity,but the quality of reconstruction is also very good.In addition,the latter algorithm has been rewritten by CUDA for parallel computing,which realize algorithm’s acceleration,and has more value.Finally,the results of simulation experiments demonstrate the necessity and effectiveness of the proposed algorithm. |
