Application Research On Electron Density Image Reconstruction Technology Of Dual-energy CT(DECT)

In the field of X-ray radiology medical imaging,Dual-energy CT(DECT)is a momentous technological progress.Because of its advantages of tissue discrimination and artifact elimination,it has attracted more and more attention in clinical applications for the past few years.It is a promising new medical imaging technology.Radiation therapy is one of the main methods for the treatment of tumor and cancer.The reconstruction and the numerical calibration of electron density images of diseased body tissue are directly related to the precision of target localization and the accuracy of radiation dose calculation.Therefore,we need to measure the electron density and its distribution of the diseased body tissue.At present,scanning phantom with CT is comm,only used to obtain the electron density image of the diseased tissue in clinical.However,this method have some problems such as high cost,tedious operations and inaccurate value.In addition,the DECT products of major digital medical equipment manufacturers at home and abroad do not directly provide electron density images.On the other hand,the traditional CT based on the absorption mechanism is unable to provide enough imaging contrast for those materials made of light elements.It leads to the emergence of phase contrast CT imaging technology arises.The basic principle of phase contrast CT is that when X-rays pass through an object,it will result in phase shift as well as attenuating,and for the materials made of light elements,the phase change of X-ray is about one thousand times more sensitive than the change of the absorption value.So the phase contrast CT imaging has a higher spatial resolution than the traditional CT in the imaging of the weak absorption materials composed of light elements.Theoretical studies have shown that the electron density image can be reconstructed by the DECT imaging system,and then the phase contrast image can be obtained.Therefore,the implementation of phase contrast CT imaging using DECT is of high theoretical value and clinical significance.Based on the two aspects mentioned above,this paper proposes a method to implement the reconstruction and the numerical calibration of DECT's electron density images.First of all,the theoretical electron density image was calculated and the monochromatic image of X-Ray linear attenuation coefficients under two different energy levels was acquired.Then,the combination of X-ray linear attenuation coefficients under the high and low energy levels was linearly fitted with the theoretical electron density values;meanwhile the corresponding goodness of fit was calculated.Finally,the reconstruction and the numerical calibration of electron density image of DECT was realized by virtue of the best the goodness of fit.The calibration results of simulation and actual data show the accuracy and effectiveness of this method.The basic idea of the two material decomposition algorithm is to select two kinds of materials with large difference in linear attenuation characteristics as the basis pairs.The linear attenuation coefficient of the scanned objects can be expressed as a linear combination of those of two basis materials.Theoretical analysis shows that the closer the linear attenuation characteristics of the basis material to the scanned objects,the better the effect of materials discrimination.However,the organs and tissues of the human body are actually made up of a variety of materials.It brings about challenges for the two material decomposition algorithm.Multi-material decomposition(MMD)algorithm augments the kinds of basis material,and then the selection range of the basis material is more extensive.This paper refines the MMD algorithm and realizes the reconstruction of the electron density images on this.Both the numerical simulation and that clinical data show that the electron density obtained using based on the refined MMD algorithm possess higher in image quality and reveals much more abundant information.It indicates new directions for wider clinical application and research of electron density images.