Preparation and characterization of polyurethane optical phantoms

We describe a method for the preparation of a polyurethane phantom to simulate the optical properties of biologic tissues at two wavelengths in the visible and near-infrared spectral range. We characterize the addition of added molecular absorbers with relatively narrow absorption bands [full width at half maximum (FWHM) 32 and $76nm$ for Epolight 6084 and 4148, respectively] for independent absorption at $690nm$ for absorption up to $5cm−1$, and $830nm$ for absorptions up to $3cm−1$. Absorption by both dyes is linear with concentration in these respective regions and is consistent in polyurethane both before and after curing. The dyes are stable over long durations with no more than 4% change. The absorption of visible light by polyurethane decreases with time and is stable by one year with a drop of $0.03±0.003cm−1$ from 500 to $830nm$. The scattering properties are selected by the addition of $TiO2$ particles to the polyurethane, which we functionally describe for the 690- and $830-nm$ wavelengths as related to the weight per volume. We demonstrate that the variation in absorption and scattering properties for large batch fabrication (12 samples) is $±3%$. The optical properties of the phantoms have not significantly changed in a period of exceeding one year, which makes them suitable for use as a reference standard.