TH‐A‐213CD‐07: Feasibility of Direct L‐Shell Fluorescence Imaging of Gold Nanoparticles Using a Benchtop X‐Ray Source

Purpose: To test the feasibility of benchtop direct fluorescence imaging of small objects loaded with low concentration of gold nanoparticles (GNPs) using gold L‐shell fluorescence x‐rays for pre‐clinical in‐vivo imaging. Methods: 1‐cm diameter cylindrical plastic tubes containing saline solutions and GNPs at 2%, 0%, and 0.5% (by weight), were placed in a vertically stacked geometry and irradiated using a pencil‐beam of 40 kVp x‐rays. A Si‐PIN detector, placed at 90° with respect to the beam axis such that it had a view along the longitudinal axes of the tubes, captured the spectrum of scattered and gold L‐shell fluorescence photons from the cylinders. Keeping the detector and source positions fixed, the distance from the source to the point of interrogation was kept constant by translation of the stack of tubes vertically and horizontally in steps of 2.5 mm until all tubes were imaged. The resulting gold fluorescence signals were extracted and used to generate a rudimentary 2‐D direct fluorescence image of the tubes. Results: Gold La and Lß fluorescence signals (9.7 and 11.4 keV) were detected with very high signal‐to‐background ratios (up to a factor of 3). The direct 2‐D fluorescence image reconstructed from the experimental geometry accurately showed the positions of each tube and relative GNP concentrations. The relative signal strength from each tube had a linear correlation with GNP concentration. The current results were extrapolated to a GNP detection limit on the order of parts‐per‐million. Conclusions: 2‐D fluorescence imaging of GNP location and concentration within small objects can be accomplished by detection of gold L‐shell fluorescence x‐rays. The current benchtop experimental setup can be easily adapted for in‐/ex‐vivo imaging. After further optimization, this setup can be used to image intra‐tumoral distribution of GNPs in vivo during pre‐clinical animal studies.