Magdalena Bazalova, Presenter: Nothing to Disclose

Lei Xing PhD, Abstract Co-Author: Research Grant, Varian Medical Systems, Inc

Rebecca Fahrig PhD, Abstract Co-Author: Research Grant, Siemens AG Research Consultant, Siemens AG

Purpose/Objective(s): X-ray fluorescence CT (XFCT) has shown promise for molecular imaging of probes containing high atomic number elements, such as gold nanoparticles. Up to date, XFCT has been induced by kilovoltage photon beams due to the high photoelectric effect interaction probability. Here we compare XFCT imaging induced by photon, electron, and proton beams of two energies. Materials/Methods: A digital 2-cm diameter phantom with four 5 mm cylindrical vials with gold solutions of 10-50 mgAu/mL was built in TOPAS, a MC simulation tool based on GEANT4. The phantom was imaged with XFCT induced by 81 keV and 10 MeV photon, 10 MeV and 100 MeV electron, and 100 and 250 MeV proton beams. First-generation CT geometry with 1×1 mm pencil beams of 5×105 particles with 0.5-mm translation and 2°-rotation steps was modeled using the GEANT4 time feature. Scattered x-rays were detected on an idealized 5 cm-diameter spherical detector with 0.5 keV energy bins. XFCT images were reconstructed with filtered back-projection using the net count of Kα (67.2 and 69.0 keV) gold x-rays determined by linear interpolation of the neighboring energy bins. Results: For a single pencil beam position, the number of detected gold Kα x-rays induced by the 81 keV photon beam was ~35 and ~150 times higher than for the electron and proton beam induced fluorescence, respectively. However, the signal-to-background ratio for the proton beam induced fluorescence was by a factor of 1.3 to 3.4 higher than for the 81 keV photon beam induced fluorescence due to the low x-ray contamination in the proton-induced x-ray spectra. As summarized in Table 1, XFCT gold imaging sensitivity was the highest in the 81 keV x-ray images (0.9 mgAu/mL) and it was the lowest in the 10 MeV x-ray images (52.3 mgAu/mL). The detection limits were 4.7 and 8.5 mgAu/mL for 100 MeV electron and 250 MeV proton XFCT images, respectively. The mean imaging dose was approximately 2-3 orders of magnitude higher in electron and proton XFCT compared to 81 keV x-ray XFCT (Table 1). Conclusions: Our Monte Carlo study demonstrates that XFCT imaging of small objects achieves the best performance when induced with kilovoltage x-ray beams. Due to the high imaging dose, electron and proton induced XFCT might be a feasible ex-vivo imaging technique. Acknowledgements: We would like to thank Jan Schuemann and Joseph Perl from TOPAS collaboration for their help with proton fluorescence simulations. Table 1: XFCT detection limits (mgAu/mL) and mean imaging dose (mGy) for the studied protocols.   81 keV photons 10 MeV photons 10 MeV electrons 100 MeV electrons 100 MeV protons 250 MeV protons Detection limit (mgAu/mL) 0.9 52.3 9.7 4.7 12.1 8.5 Imaging dose (mGy) 0.1 1.2 56.6 56.1 238.5 118.8  

Bazalova, M, Xing, L, Fahrig, R, X-ray Fluorescence Computed Tomography Induced by Photon, Electron, and Proton Beams.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14043046.html