Optical finger phantom with realistic optical properties

Existing optical phantoms often do not represent realistic optical and geometrical properties. This study aimed to fabricate a homogeneous silicone finger phantom that closely mimics the reflectance and transmittance characteristics of a human finger by precisely adjusting the absorption and reduced scattering coefficients in the visible wavelength range. The absorption and reduced scattering coefficients of a human finger were determined using a custom inverse model tailored for an integrating sphere system designed for cylindrical media illuminated along the barrel. To reproduce the retrieved optical properties in silicone, a reference database was created by characterizing the absorption spectra of 15 pigments dispersed in a silicone matrix. An automated fitting algorithm identified five suitable absorbing pigments, and their required concentrations were calculated to match the target absorption spectrum. The reduced scattering coefficient was independently controlled by varying the concentration of zirconium dioxide particles. An alginate mould was used to capture the finger geometry, ensuring anatomical accuracy of the phantom. The fabricated silicone finger phantom closely matched the human finger in both transmittance and reflectance, as well as in its anatomical shape. The ΔE ₂₀₀₀ value between the reflectance spectra of the human and silicone fingers was found to be 0.85. Under transmittance-mode illumination, light propagation within the silicone phantom agreed well with that of a human finger, both in visual appearance and in spatial light distribution. A method was developed to fabricate silicone finger phantoms with accurately matched optical and anatomical properties.