X-ray luminescence computed tomography (XLCT) technology uses X-ray excitation to stimulate specific luminescent materials at the nanoscale, termed phosphor nanoparticles (PNPs), to produce near-infrared light. Photodetectors then capture the emitted near-infrared light signals from these excited PNPs. Through suitable algorithms, the distribution of PNPs within biological tissues can be visualized. This method allows for structural and functional insights into biological tissues, showing great potential for advancement. There are two main types of XLCT systems: narrow-beam and cone-beam. The narrow-beam XLCT system exhibits higher spatial resolution, albeit at the cost of lower X-ray utilization efficiency. This inefficiency results in extended imaging times, limiting its potential for clinical use. Conversely, the cone-beam XLCT system improves X-ray efficiency and shortens detection time. However, the quality of the reconstructed images tends to be lower due to detection angle limitations. To overcome these challenges, there is a need for an innovative XLCT system that realizes rapid and highly sensitive data collection while also maximizing the use of X-ray technology. By addressing these issues, the clinical limitations of XLCT can be reduced to pave the way for its further development, thereby unlocking a plethora of possibilities.

This study introduces a new cone-beam XLCT system based on photon-counting measurements, complemented by an associated reconstruction method. Through the synergistic collaboration between the field-programmable gate array (FPGA) based sub-sampling unit and upper-level control unit, the system realizes automated multi-channel measurements. This integration shortens data acquisition time, boosts experimental efficiency, and mitigates the risks associated with X-ray exposure. After the completion of system implementation, we conduct experimental validation of the system and methodology. Specifically, a fabricated phantom is subjected to multi-angle projection measurements using the established system, and image reconstruction and evaluation are performed using the Tikhonov reconstruction algorithm.

The results of the dual target phantom experiment indicate that under the conditions of a cylindrical phantom radius of 40 mm, target radius of 6 mm, and distance of 14 mm from the dual target phantom (Fig.2), the similarity coefficient (DICE) of the reconstructed image of the dual target phantom exceeds 50% under six-angle cone-beam X-ray irradiation. Furthermore, the system fidelity (SF) exceeds 0.7 (Table 1). In the phantom experiment of dual targets with different concentrations, the system proposed in this study effectively distinguishes dual targets with a mass concentration difference of more than 3 mg/mL. The DICE of the reconstruction image maintains over 50%, SF remains over 0.7, and reconstruction concentration error (RCE) is also over 0.7 (Table 2). These phantom experiment results confirm the good fidelity and resolution capability of the proposed system. Nevertheless, numerous factors potentially degrade the experimental outcomes, such as the attenuation and scattering of X-ray beams in the XLCT system, the physical and chemical composition of the target body, or even uneven concentration distribution. Additionally, artifacts appear in the reconstructed images. In the future, our research will focus on optimizing algorithms and reducing noise to enhance the application of cone-beam XLCT for in vivo experiments.

This study comprehensively considers the advantages and disadvantages of two imaging methods in XLCT and proposes a photon-counting-based multi-channel cone-beam XLCT system. The system automation for multi-angle measurements is realized via FPGA and host computer interaction. Specifically, multi-angle cone-beam irradiation reduces data acquisition time, while photon-counting measurement enhances the system sensitivity. Furthermore, a phantom experiment is conducted to validate the effectiveness and practicality of the proposed system and algorithm. The results demonstrate a significant reduction in data acquisition time and an improvement in the utilization of X-rays.