Rendering of Scattering Luminescent Phantoms with a Full-Cascade Monte Carlo Framework

Accurate modeling of light transport in turbid luminescent media is essential for biomedical optical diagnostics and the design of phosphor-converted materials. However, bispectral surface reflectance models and volumetric models limited to a single Stokes shift cannot capture the coupled multiple scattering, re-absorption and re-emission that determine the appearance of these media. Here, we present a GPU-accelerated forward Monte Carlo framework that solves the radiative transfer equation for elastically scattered and luminescent light on tetrahedral meshes of arbitrary geometry. The framework was benchmarked against two previously validated codes, a luminescence cascade simulator and a tetrahedral reverse path tracer, and was experimentally validated using silicone phantoms containing ${\mathrm{ZrO}}_2$ scatterers and two concentrations of Rhodamine 6G, imaged in a calibrated photobox. The renderings reproduced the photographs with mean CIEDE2000 color differences between $\Delta E=0.94$ and $1.24$, close to the human perception threshold. Without luminescence (quantum yield ${\Phi }_f=0$), the color difference increased to up to $\Delta E=7.04$. Restricting each photon to a single conversion increased it to up to $\Delta E=2.16$, with a larger effect at the higher dye concentration. The framework can support the design of phosphor converters and luminescence imaging systems.