Numerical and Monte Carlo Simulation for Polychromatic L-shell X-ray Fluorescence Computed Tomography Based on Pinhole Collimator with Sheet-Beam Geometry

X-ray fluorescence computed tomography (XFCT) has attracted wide attention due to its ability to simultaneously and nondestructively obtain structural and elemental distribution information within samples. In this paper, we presented an image system based on the pinhole collimator for the polychromatic L-shell XFCT to reduce time consumption and improve the detection limit. First, the imaging system model was expressed by formulas and discretized. Then, two phantoms (A and B) were scanned by numerical simulation and Monte Carlo simulation. Both phantoms with the same diameter (10 mm) and height (10 mm) were cylinders filled with PMMA, and embedded with GNP-loaded cylinders. The phantom A was inserted by six 1.5 mm-diameter cylinders with different Au concentrations ranging from 0.2% to 1.2%. The phantom B was inserted by eight cylinders with the same Au concentration (1%), but a radius ranging from 0.1 mm to 0.8 mm. Finally, the reconstruction of the XFCT images was performed using the method with and without absorption correction, respectively. The feasibility of XFCT system presented in this paper was demonstrated by the numerical simulation and the Monte Carlo simulation. The results show that absorption attenuation can be corrected by the presented method, and the contrast to noise ratio (CNR) is proportional to Au concentration but almost remains unchanged with the radius of GNP-loaded cylinders, which may provide the necessary justification for further optimization of the imaging system.