SNR Analysis of Polychromatic Fan-Beam XFCT System Using a CZT Detector Array

X-ray fluorescence computed tomography (XFCT), which is considered as a promising approach to determine the bio-distribution of high Z elements such as gadolinium (Gd) and gold (Au), is carried out more on the benchtop XFCT systems with polychromatic x-rays produced by x-ray tubes in recent years, which means that the XRF signal stimulated by the polychromatic x-ray source is strongly affected by the Compton-scattered photons. In order to reduce the dose of the scattered photons with energies near the energy of the fluorescent photons, filters made of lead (Pb), copper (Cu), aluminum (Al), tungsten (W) or tin (Sn) were used in previous studies. However, using filters will reduce the intensity of the incident beam, which causes larger statistical noises. In addition, the energy response of the detector will weaken the effect of filtering, which also causes the decrease of signal quality. In this paper, a set of simulations were carried out to investigate the signal-to-noise ratio (SNR) of the projection data detected by a CZT photon counting detector array in a benchtop fan-beam XFCT system. The phantom is stimulated by a polychromatic X-ray source filtered by different filters made of Pb, W, Sn, Cu, and Al. Simulations show that due to the statistical noises and the energy response of CZT linear array detector, optimizing the incident X-ray spectrum using common filters doesn't help improving the SNR of the projection data at a fixed power of x-ray tube.