High-resolution X-ray fluorescence imaging of silver-based contrast agents by EDXRF spectrometry: A preclinical study

X-ray fluorescence computed tomography is a promising imaging technique for mapping the spatial distribution of heavy elements in biomedical applications. Silver (Ag)-based agents have been identified as radiosensitizers and imaging tracers due to their high atomic number (Z = 47), which enhances local dose deposition through increased photoelectric absorption, as well as their ability to promote reactive oxygen species generation under irradiation. These properties make Ag-based agents promising candidates for enhancing radiotherapy efficacy while simultaneously enabling X-ray-based imaging detection. In this work, an experimental setup has been developed and characterized to evaluate the feasibility to map Ag-based agents by means of energy dispersive X-ray detection using the Amptek XR100 cadmium telluride (CdTe)-based spectrometer. The energy response of the spectrometer has been validated up to 85 keV, confirming its ability to resolve the Ag Kα and Kβ lines. Aqueous AgNO₃ solutions with concentration from 0.033 up to 0.100% w/w, have been used to determine the system's detection sensitivity, yielding a limit of detection K_α = 0.004% w/w. The overall imaging performance was assessed by scanning a cylindrical PMMA phantom containing Ag samples using a collimated X-ray beam. The resulting fluorescence maps have been reconstructed using the MLEM algorithm stabilized with total variation regularization. The reconstruction showed a linear correlation between reconstructed signal intensity and the Ag concentration (R² = 0.999) and a minimum detectable concentration of 0.019% w/w. This evidence supports the ability of the developed experimental setup to obtain quantitative XFCT images of Ag-based agents. Furthermore, the system's quantitative accuracy validates its potential for integration into theranostic protocols.