title: Optical absorption characteristics in the assessment of powder phosphor-based x-ray detectors: from nano- to micro-scale.
abstract: X-ray phosphor-based detectors have enormously improved the quality of medical imaging examinations through the optimization of optical diffusion. In recent years, with the development of science and technology in the field of materials, improved powder phosphors require structural and optical properties that contribute to better optical signal propagation. The purpose of this paper was to provide a quantitative and qualitative understanding of the optical absorption characteristics in the assessment of powder phosphor-based detectors (from nano- scale up to micro-scale). Variations on the optical absorption parameters (i.e. the light extinction coefficient [Formula: see text] and the percentage probability of light absorption p%) were evaluated based on Mie calculations examining a wide range of light wavelengths, particle refractive indices and sizes. To model and assess the effects of the aforementioned parameters on optical diffusion, Monte Carlo simulation techniques were employed considering: (i) phosphors of different layer thickness, 100 μm (thin layer) and 300 μm (thick layer), respectively, (ii) light extinction coefficient values, 1, 3 and 6 μm(-1), and (iii) percentage probability of light absorption p% in the range 10(-4)-10(-2). Results showed that the [Formula: see text] coefficient is high for phosphor grains in the submicron scale and for low light wavelengths. At higher wavelengths (above 650 nm), optical quanta follow approximately similar depths until interaction for grain diameter 500 nm and 1 μm. Regarding the variability of the refractive index, high variations of the [Formula: see text] coefficient occurred above 1.6. Furthermore, results derived from Monte Carlo modeling showed that high spatial resolution phosphors can be accomplished by increasing the [Formula: see text] parameter. More specifically, the FWHM was found to decrease (i.e. higher resolution): (i) 4.8% at 100 μm and (ii) 9.5%, at 300 μm layer thickness. This study attempted to examine the role of the optical absorption parameters on optical diffusion studies. A significant outcome of the present investigation was that the improvement of phosphor spatial resolution without decreasing the light collection efficiency too much can be better achieved by increasing the parameter [Formula: see text] rather than the parameter p%.
authors.affiliation: Department of Biomedical Engineering, Technological Educational Institute, 122 10 Athens, Greece.
authors.forename: P F
authors.initials: PF
authors.lastname: Liaparinos
mesh_terms: D003198:Computer Simulation; D003952:Diagnostic Imaging / Q000379:methods*; D006801:Humans; D008027:Light; D049449:Luminescence; D008163:Luminescent Measurements / Q000379:methods*; D008962:Models, Theoretical; D009010:Monte Carlo Method; D055620:Optical Phenomena; D010758:Phosphorus; D011208:Powders / Q000737:chemistry*; D012542:Scattering, Radiation; D014963:X-Ray Intensifying Screens; D014965:X-Rays
chemical_list: D011208:Powders; D010758:Phosphorus