Study On Metal Artifact Reduction In Cone Beam Computed Tomography Reconstruction

Cone beam computed tomography(CBCT)is a widely researched CT imaging technology.Compared to traditional 2D scanners,CBCT scanner can improve the speed of scanning and the quality of reconstructed CT images.CBCT scanner has become an important tool in image guided radiation therapy and industrial inspection field.However,when the scan field exists metal or other objects with high attenuation,artifacts will appear in the reconstructed images.The existence of metal artifacts will affect the quality of CT images and degrade the diagnostic value,so the research on the metal artifacts reduction about CBCT imaging is always one of the most important projects.This thesis will mainly focus on how to reduce the metal artifacts in CBCT.The theoretical basis of CT imaging and CBCT reconstruction will be introduced first in this thesis,the causes of metal artifacts in cone beam CT will be analyzed and discussed too.The thesis also introduces the most classical CT metal artifacts reduction methods in detail,and compare the difference between them.After the research on existing methods,this thesis proposes a metal artifacts reduction method which is based on the fusion of projection images.The metal artifacts problem has appeared when the CT only has single row detectors,many methods have been proposed to solve this problem.The methods for metal artifacts reduction can be divided into two categories: projection based metal artifact reduction and iteration based reconstruction method,this thesis will focus on the projection based method.The projection based method is aimed to replace the affected projection effectively,the interpolation methods are used to replace the metal affected projection data,though this method can reduce the metal artifacts partly,new artifacts can be introduced into the reconstructed CT images.The loss of tissue information in CT images when using interpolation methods is also a problem,researchers proposed prior image methods to solve it,forward projection will be applied to the prior images to get the prior projection,the metal affected data in the original projection will be replaced by the corresponding data in the prior projection.In this thesis,the prior images will be obtained by fusion,the projection correction step will fuse the prior projection and the original projection to avoid problems caused by interpolation.The proposed method will be experimented and the results will be compared with other methods,it is proved the method has good performance in CBCT metal artifact reduction and can be used in many different cases.