Study On Image Reconstruction Algorithm Of Dual-energy CT

Since the advent of computed tomography (CT), it has been widely used inmedical, industrial, agriculture and forestry, safety inspection, aerospace and other fieldsfor its advantages of high precision, non-destructive, visualization, etc. CT is atechnique that can obtain the inner structure images of materials with multiple X-rayprojections taken at different angles around the scanned materials. The technique of dualenergy CT was proposed in1976, and quickly became the hot topic in detection fields,especially the medical field and the safety inspection field. In theory, dual energy CThas a high detection accuracy compared to the conventional single-energy CT, and it isable to obtain the material information of the scanned object accurately—electrondensity and effective atomic number of the substance, In this way will more accuratelydetermine the type of the scanned object. Dual energy CT technique is particularlyimportant in the explosive detecting witch can not use the shape of the materialinformation, but the traditional CT can only access the materials’ electron density, thisadvantage makes dual-energy CT became one of the most active areas in the study ofX-ray CT.In dual energy CT the object is scanned with two distinct energy spectrums. Imagereconstruction algorithm is one important part of the CT technology, dual energy CT isno exception. There are two different decomposition model of attenuation coefficient:photoelectric effect and the Compton scattering effect decomposition model and basismaterial decomposition model, the latter is selected in this paper. Basis materialdecomposition model is that the attenuation coefficient can be expressed as a linearcombination of two attenuation coefficient functions of two basis materials. Accordingto the basis material decomposition model, the projection functions of the high and lowenergy spectrum of dual energy CT is obtained, and then the lookup table is established.The projection matching of high and low projections to get two sets of basis materialprojections of decomposition coefficient is realized by the use of lookup table. Then thedecomposition coefficient can be obtained by the use of filtered backprojection(FBP)reconstruction algorithm. Finally, the electron density and effective atomic number ofthe scanned object can be calculated.Total variation(TV) maintain the image edge better in the process of imagedenoising, which makes TV become a hot topic in the study of image denoising filed, at the same time it makes certain contribution to the development of the algebraicreconstruction. Its main idea is to model the image denoising as a TV minimizationprocess, is to make the image reaches a flat state. Due to the artifacts of the obtainedelectron density and effective atomic number images, and in order to make the imagesmore accurately, in this paper, TV minimization is applied to the dual energy CT to dealwith the obtained electron density and effective atomic number images, to get a smoothelectron density and effective atomic number images. The simulation results show thatdual energy CT could obtain the electron density and effective atomic number ofmaterials, meanwhile, with the introduction of TV, dual energy CT reconstruction iscapable of getting better quality images of materials’ electron density and effectiveatomic number, and is more conducive to materials’ detection.