A Study On Multi-energy X-ray CT Technology And Its Application Based On Photon Counting Detector

X-ray Computed Tomography(CT)technique,which uses X-ray to scan the examination object and employs algorithms to reconstruct the internal cross-section images of the examination object,plays an important role in the diagnosis and treatment of diseases.With the rapid development of the detector technology,the multi-energy X-ray CT technique based on photon counting detector has being developed.The Multi-energy X-ray CT can collect the transmitted X-ray from the examination object into several energy-bins,which carrys rich material attenuation information.Then the attenuation information is used to reconstruct the CT images of the object.The multi-energy X-ray CT technique can display the internal structure of the examination object,and have the ability of discriminating the material properties which is lacked in the traditional X-ray CT imaging.In recent years,the multi-energy X-ray CT technique based on photon counting detector has become a research focus in the CT imaging field.To improve the quality of the photon counting X-ray CT images,both projection-based and image-based weighting imaging schemes using filtered back-projection(FBP)algorithm were firstly investigated throughly in this paper.Both the weighting imaging schemes make full use of the X-ray attenuation information collected by the photon counting detector of each energy bin to construct weights,then the weights are assigned to each energy bin,and the full spectral image is a linear combination of each energy bin.Based on the above weighting imaging schemes,the effect of the number of energy bins on the image quality of full spectral image was studied.Furthermore,in the image-based weighting imaging scheme,the transmitted photons was collected into each energy bin,thus the number of photons was reduced as compared to energy integrating imaging scheme,and the signal-to-noise ratio of the projection data was decreased,thereby possibly leading to high noise in separate images from each energy bin with FBP algorithm,and degrading the full spectral image quality.To solve the above problems,a multi-energy X-ray CT statistical reconstruction algorithm based on maximum a posteriori(MAP)was proposed,and its performance was analyzed and evaluated.In addition,for K-edge imaging,the effect of energy bin width was analyzed with respect to the K-edge image quality.In the applications of projection-based weighting imaging and K-edge imaging,the projection-based weighting imaging scheme was proposed for photon counting breast CT temporal subtraction imaging,and the K-edge imaging technique was proposed for photon counting dual energy breast CT subtraction imaging,and the quality of these two types of subtraction images were analyzed and evaluated.The simulation results show that,compared with the traditional energy integrating scheme,both projection-based weighting and image-based weighting imaging schemes show effective improvement with respect to the contrast-to-noise ratio(CNR)of the full spectrum images,and both the CNRs of the calcium and iodine increase as a function of the number of energy bins.The CNR of the full spectrum image reconstructed by the image-based weighting imaging is higher than the projection-based weighting imaging scheme.Compared with the image-based weighting imaging scheme using FBP algorithm,the image-based weighting imaging scheme using MAP statistical algorithm can significantly improve the CNR of the full spectrum image.In addition,the K-edge imaging technique can improve the CNR of the contrast element image,and the appropriate choice of the energy bin width can make the CNR of the K-edge image to be highest.Photon counting detector based breast CT subtraction imaging can eliminate the interference of normal tissue signals,and highlight the contrast element signals.Compared with energy integrating imaging,in the photon counting detector based breast CT temporal subtraction imaging,the CNR of the subtraction images obtained by projection-based weighting imaging can be significantly improved.In the photon counting detector based dual energy breast CT subtraction imaging,the appropriate choice of high and low-energy bins can maximize the CNR of the subtraction image.