Optical photon transport in powdered‐phosphor scintillators. Part 1. Multiple‐scattering and validity of the Boltzmann transport equation

Abstract

Results: Disagreement between BTE and EMM approaches increased with increasing n and p f . For 25 the thinnest screen (t = 50 µm), highest packing fill (p f = 0.5) and largest relative refractive index (n = 5), the BTE model underestimated the absorbed fraction by 40% and the MTF50 by 20%. However, the BTE and EMM predictions agreed well at all simulated packing densities when n ≤ 2. Swank's model agreed with the BTE well when the screen was thick enough to be considered turbid. Conclusion:Although assumptions of the BTE are violated in powdered-phosphor screens at 30 moderate-to-high packing densities, these lead to negligible effects in the modeling of optical transport for typical phosphor-binder relative refractive indices (n ≤ 2), such as those based on Gd 2 O 2 S:Tb. Swank's diffusion equation solution is an adequate approximation to the BTE if the turbidity condition is satisfied.

Modelling the transport of optical photons in scintillation detectors for diagnostic and radiotherapy imaging

“…The DOSxyznrc code was used to generate the photon absorption probability distribution function and the optical photon transport was modelled by DETECTII routines (Fasbender et al , 2003; Kausch et al , 1999; Radcliffe et al , 1993). More recently, Poludniowski and Evans modelled the light transport in powdered-phosphor scintillator screens using a combined method based on the Boltzmann transport equations (Poludniowski et al , 2013a; Poludniowski et al , 2013b). The three-dimensional dose distribution was calculated using DOSRZnrc.…”

“…Analytical models and numerical simulations have also been applied to optical modelling (Swindell, 1991; Swindell et al , 1991; Evans et al , 2006; Freed et al , 2010; Poludniowski et al, 2013a; Poludniowski et al, 2013b). …”

Optical photon transport in powdered‐phosphor scintillators. Part II. Calculation of single‐scattering transport parameters

“…Optical transport in the screens was conducted using the Boltzmann transport equation Monte Carlo code described in Part I of this work. 2 The grain radius in the Lanex Fast screens was assumed to be 4.25 μm. This corresponds to the middle of the range of median diameters (8-9 μm) inferred from the patent literature for Eastman Kodak high-speed screens.…”

“…Powdered-phosphor screens have been used widely in medical imaging as discussed in Part I of this work. 2 Despite the quantum gain from the use of powderedphosphors, light scattering and absorption in the screen leads to a degradation in the modulation transfer function (MTF) and light-collection efficiency. This depends on the geometry and structure of the screen and there is interest in characterizing and optimizing such effects (see references to Part I for further details).…”

Light wavelength effects in submicrometer phosphor materials using Mie scattering and Monte Carlo simulation

“…The light wavelength affects the overall performance of light emitted by the phosphor layer changing the imaging characteristics of the detector. The transmission of light can be described by the light attenuation (absorption and scattering) either through "diffusion" theory in theoretical models 20,21 or "quantum" theory in Monte Carlo methods 8,22,23 as provided in the present study. An advantage of the present model is that it allows for investigation of screen optimization by examining particle size and packing density effects through Mie scattering theory.…”