Development of simulated pigmented lesions in an optical skin-tissue phantom: Experimental measurements in the visible and near infrared

Realistic, pigmented skin simulants (“phantoms”) can be useful in optimizing dermal laser procedures and for laser surgical training. Diffuse reflectance of skin pigmented lesions depends on the amount and distribution of the absorbing/diffusing chromophores, mainly hemoglobin and melanin, embedded in the skin layers. The reason why diffuse reflectance of benign melanocytic lesions is different from that of melanoma is still unclear. In an attempt to explain such a difference, phantoms able to simulate the diffuse reflectance of both types of pigmented skin lesions have been developed. The basic material for lesion- and skin-like phantoms is a transparent silicone rubber in which Al2O3 particles, melanin, and different types of cosmetic powders were added as diffusers and absorbers. Slabs with a minimal thickness of 100 μm were prepared to mimic lesions with different thicknesses and the skin layered structures. The optical properties of tissue phantom components, i.e., total attenuation, absorption, and scattering coefficients and phase function, have been determined in the visible and near-infrared spectral range by using direct and indirect techniques. Finally, reflectance measurements of the phantoms were performed. By varying the concentration of the scattering and absorbing particles, tissue-like layers were produced with predictable optical properties. In particular, when mixing Al2O3 particles, melanin, and cosmetic powders at suitable concentrations with the silicone rubber, diffuse reflectance of our phantoms reasonably agreed with that measured in vivo of benign and malignant pigmented lesions over a range of wavelengths from 400 to 920 nm. The proposed technique allows reproduction of skin moles. The possibility of reproducing the optical features of in vivo skin pigmented lesion measurements by means of lesion-like structures is expected to be a valuable tool to try to explain why melanoma usually appears different from benign naevi. Finally, the phantom presented in this work could be a useful tool to verify the reliability of simulation models, e.g., Monte Carlo methods, in the description of light interaction with biological tissues and subsequent rise in temperature, especially when heterogeneous structures are concerned.