Imaging efficiency optimization for x-ray fluorescence computed tomography based on Thomson scattering x-ray sources

X-ray fluorescence computed tomography (XFCT) based on Thomson scattering x-ray sources is a novel molecular imaging technique applicable in both laboratory and clinical settings. However, its practical development is limited by relatively low imaging efficiency. To address this challenge, this study presents a dual approach that simultaneously optimizes the incident x-ray energy to maximize fluorescence yield and designs a three-pinhole collimator to enhance detection sensitivity. For the element gold (Au) widely used in XFCT imaging, the optimal incident x-ray energy was determined to be 82.6 keV for a Thomson scattering x-ray source with a root mean square bandwidth of 1%. Using contrast agents containing gold solutions with Au concentrations ranging from 0.1 to 4.0 wt. %, the performance of the designed imaging system was evaluated by Monte Carlo simulations. Compared to the conventional single-pinhole collimator, the three-pinhole design provides an approximately 2.5-fold enhancement in sensitivity and lowers the detection limit for gold solution from 0.183 to 0.161 wt. %. By increasing the incident x-ray energy to 100 keV, the scatter background was significantly reduced; however, lower contrast-to-noise ratios were observed across all gold solution concentrations, owing to the reduction of fluorescence yield at elevated x-ray energies. For the designed imaging system, a spatial resolution of approximately 0.7 mm can be achieved. Using this system, a complete XFCT scan can be completed in approximately 24 s using a Thomson scattering x-ray source with a photon yield of 1013 photons/s, without inducing pulse pileup effects; meanwhile, gold solutions with a concentration as low as 0.2 wt. % can be clearly resolved at a radiation dose of 2 Gy.