Research On Fast 3D Reconstruction Algorithm Of Cone Beam CT Based On Wavelet Transform Transform

Computed Tomography(CT)has been widely used in the field of clinical medicine because of its good presentation of organs constituted of interior tissue in human body.As the information technology is developing rapidly,three-dimensional cone beam CT based on flat panel detector(FPD)is proposed which is based on the traditional two-dimensional CT.Due to the use of cone beam X-ray source and planar detector to collect the projection data of each angle of the object,the utilization ratio of X ray is greatly improved,and the scanning speed and the spatial resolution of the CT reconstruction image are improved accordingly.Due to the superiority of cone beam CT,it is used more and more widely in the field of modern medicine and industry.However,as the flat panel detector is developing rapidly,the number of detection uint is increasing gradually.The obtained scanning data with the cone beam X-Tray resource rotary scanning will become increasingly huge,and the reconstruction speed will be slowed down.For example,during image-guided radiation therapy,the radiotherapy system should provide doctors with the target image in time to achieve the purpose of tracking the tumor,thereby improving the effectiveness of radiation therapy and reducing the damage to normal tissue.Therefore,how to improve the reconstruction.speed is the focus of cone beam reconstruction algorithm.FDK algorithm is one of the most classical algorithm in cone bearn reconstruction algorithm.Because of its advantages of circular trajectory scanning,easy implementation and fast reconstruction speed,it has good reconstruction effect with the small cone angle of the ray source.Therefore,the FDK algorithm is widely used in the cone beam CT system currently.However,there are still some problems such as large amount of computation and time-consuming in the reconstruction of FDK reconstruction algorithm,which can't meet the real-time requirement.Besides,doctors have different requirements for the resolution of CT images in clinical diagnosis.To solve the problems above,this paper proposes a fast reconstruction algorithm of cone beam CT based on wavelet transform.Firstly,the corresponding wavelet transform for projection images are obtained,and the corresponding scale wavelet coefficients.are selected for FDK reconstruction.Thus,3D image data of the low resolution are obtained.According to the need,the high resolution 3D image data can also be obtained by the inverse wavelet transform of the radial images obtained from low resolution.The proposed algorithm in this paper mainly includes the following two parts:(1)Doctors have different requirements for the resolution of CT images in clinical diagnosis.If the CT image with low resolution is demanded,the projection image can be processed by dimension reduction and then be reconstructed by FDK algorithm when the resolution of the projection image is high enough.In this paper,two methods of image dimensionality reduction by Gauss Pyramid decomposition and wavelet transform are introduced,and the steps of combining with FDK algorithm to reconstruct low resolution CT image are illustrated.(2)Based on the demands of different resolution CT images and real-time,the method proposed in this paper can obtain high resolution CT images by inverse wavelet transform and Lanczos-3 interpolation based on the reconstruction of low resolution CT images.The experimental data shows that this method can not only provide a different resolution of the 3D image data,but also can increase the reconstruction speed more than one times when the same resolution and similar precision high resolution 3D image data is obtained compared with the traditional FDK algorithm.