Reconstruction And Attenuation Correction Of X-Ray Fluorescence Computed Tomography Imaging

X-ray computed tomography(CT)imaging plays a pivotal role in the diagnosis,staging,treatment planning,and therapeutic assessment of various diseases.It is also indispensable in preclinical small animal imaging research.The modality,however,falls short in providing molecular features.How to add molecular imaging information on top of anatomical CT images represents a significant unmet need in clinical practice and in vivo animal imaging studies.A technique using X-ray excitable nanophosphors has been suggested for simultaneous imaging of anatomy and molecular features.While the approach shows extremely high sensitivity and spatial resolution,limited penetration depth of optical signal may render the X-ray luminescence CT(XLCT)to preclinical use and certain niche clinical applications.X-ray Fluorescence Computed Tomography(XFCT)is a widely-used experimental technique for investigating the spatial distribution of elements in a sample.However,image reconstruction for this technique is more difficult than for transmission tomography,one problem being self-absorption.In this work,we make use of known quantities and unknown density of elements of interest to express unknown attenuation maps.The attenuation maps are added to the contribution value of the pixel in the Maximum Likelihood Expectation Maximization(MLEM)reconstruction method.Results indicate that the relative error is less than 14.1%,which shows that this method can effectively correct XFCT.Ordered Subsets Expectation Maximization(OSEM),which has high quality of image reconstruction and short computation time,has been applied to the imaging of endogenous CT(such as SPECT,PET,synchrotron radiation X-ray fluorescence CT)image reconstruction.In this paper,the OSEM algorithm is applied to reconstruct the image of X-ray fluorescence CT,and attenuation correction is carried out by introducing the attenuation correction factor.