Monte Carlo study for pinhole X-ray fluorescence imaging of gadolinium nanoparticles

This work aims to develop a Monte Carlo (MC) model of pinhole x-ray fluorescence imaging for gadolinium nanoparticles (GdNPs) in a cylindrical water phantom and to derive the relationship between imaging dose and quality for different x-ray spectra. We constructed four Gd columns in the water phantom which had different concentrations: 0.01%, 0.03%, 0.06%, and 0.09% by weight of Gd The water phantom with and without Gd columns were irradiated by fan beams of 51 keV and 60 keV monochromatic x-rays. The spectrum of 110 kVp polychromatic x-rays with 3-mm-thick Be and 2-mm-thick Al filter was extracted from SpekCalc code. 110 kVp x-rays with 3-mm-thick Be and 0.3-mm-thick W filter were also used to irradiate the phantoms. The images were evaluated by Contrast to Noise Ratio (CNR). The imaging dose to water of each x-ray source was also calculated by MC simulations. Finally, we could estimate the dose required to achieve CNR=3. The spectrum of 110 kVp x-ray with 3-mm-thick Be and 0.3-mm-thick Wfilter was shown to be the best incident x-ray in terms of reducing dose while achieve high quality image. The MC simulations demonstrated the feasibility of pinhole x-ray fluorescence imaging of Gd nanoparticles.