Monte carlo study of detection limit for gold nanoparticles within small animal sized object during benchtop X-ray fluorescence computed tomography

This Monte Carlo (MC) study investigated theoretically achievable detection limits of gold nanoparticles (GNPs) present within a small-animal-sized phantom during benchtop x-ray fluorescence (XRF) computed tomography (XFCT) imaging based on the detection of gold K-shell XRF photons emitted from GNPs. The MC model was based on our experimental benchtop cone-beam XFCT system, reflecting an anticipated upgrade adopting a larger field-of-view pixelated cadmium-telluride detector that fully covers a 3 cm-diameter PMMA phantom including three 6 mm-diameter cylindrical holes filled with various concentrations of GNPs. It was validated by comparing the MC results with experimental data acquired under identical conditions using a 1.8 mm-Sn-filtered 125 kVp beam. The MC simulations were then extended to investigate GNP detection limits across a range of x-ray doses, GNP concentrations, and incident x-ray beam spectra. Assuming an ideal detector, the GNP detection limits of 104-140 ppm at 1.775 cGy and 69-88 ppm at 3.55 cGy were achievable with the 1.8 mm Sn-filtered 125 kVp beam. When hypothetical monochromatic beams with their energy above the gold K-edge were employed, the GNP detection limits were improved by up to three-folds at a given dose (e.g., 34-70 ppm at 1.775 cGy with the 85 keV beam).