Tunable melanin-mimicking polyurethane films for evaluating the accuracy of quantitative diffuse optical spectroscopy

Quantitative diffuse optical spectroscopy (DOS) is used in clinical research to non-invasively characterize deep tissue composition and metabolism by measuring its near-infrared optical properties. However, it has been observed that absorption from epidermal melanin can reduce signal strength and decrease the accuracy of absolute optical property measurements. With the ultimate goal of developing techniques to correct for these effects, we first needed a reproducible phantom system that mimics epidermal melanin absorption. Here we report the fabrication and evaluation of skin phantoms based upon widely available polyurethane adhesive dressing films with tunable near-infrared absorption introduced by desktop laser printing. These easy-to-fabricate films reproduced physiological melanin absorption in the range of 600 to 1000nm and exhibited good reproducibility (<8% inter-sample variation over 20 replicates). We applied films of varying opacity to homogenous tissue-simulating phantoms to demonstrate their effect on absolute optical properties measurements by frequency-domain near-infrared spectroscopy (FD-NIRS).