Room: Davidson Ballroom B
Purpose: To find the optimal spectrometer arrangement and collimation strategy for X-ray Fluorescence CT (XFCT) imaging of gold nanoparticle (AuNP) solutions for a table-top imaging system.
Methods: A 2.5cm-diameter cylindrical water phantom containing 4mm-diameter vials with AuNP concentrations of 0.5%-3% by weight was modelled by TOPAS, a Monte Carlo software package. The phantom was irradiated to 30 mGy by a 0.5mm lead-filtered 120kVp 1-mm wide x-ray pencil beam to yield Au K-shell fluorescent x-rays, with 25 1-mm translation and 180 2-degree rotation steps. Eight cadmium telluride (CdTe) spectrometers available in our lab were placed 1.25cm away from the phantom edge. The detected x-ray spectra were corrected for detector response via the stripping method to extract the fluorescence signal with an energy resolution of 1keV. Two spectrometer angular configurations, namely isotropic and back-scattered arrangements, and the addition of 2mm diameter tungsten collimators in front of each spectrometer were considered in optimizing the contrast-to-noise ratio (CNR) for each XFCT image reconstructed with filtered backprojection. The CNR was evaluated to find the lowest AuNP concentration for each image based on the Rose criterion.
Results: The uncollimated back-scattered spectrometer arrangement could detect lower concentrations of AuNPs compared to the isotropic spectrometer arrangement, with a AuNP sensitivity limit of 0.26% versus 0.61% due to the decreasing energy of the background photons with increased scattering angle. Collimating the excitation beam lowered the AuNP concentration limit to 0.21% from 0.26%. However, the collimated back-scattered spectrometer arrangement image had a worse AuNP sensitivity limit of 1.33%. Ring artifacts in the collimated XFCT images impacted these results.
Conclusion: This work demonstrated the effect of improving AuNP imaging sensitivity for our table-top XFCT system with multiple spectrometers placed in an optimized back-scattered arrangement. Use of a tightly-collimated excitation beam and ring correction algorithm will further improve the image quality.