Preliminary results on the use of a noninvasive instrument for the evaluation of the depth of pigmented skin lesions: numerical simulations and experimental measurements

The early detection of cutaneous pigmented lesions is an important aid to the clinician in recognizing malignant melanoma. In an attempt to correlate the depth of a pigmented skin lesion with its malignant potential, phantoms able to simulate the diffuse reflectance of some lesions of different thicknesses were manufactured and tested to validate a diagnostic instrument developed in-house. Such optical skin-tissue phantoms may be useful for accelerating and optimizing the diagnosis of suspicious lesions of the skin. In fact, benign melanocytic lesions are different in terms of their diffuse reflectance from melanoma. The diffuse reflectance of pigmented skin lesions depends on the amount and distribution of the absorbing/diffusing chromophores embedded in the skin layers. The basic phantom material is a PVA hydrogel in which appropriate amounts of optical scatter are added extraneously at the time of formation to achieve tunability of the optical properties. Liquid Indian ink is used to simulate melanin and all the other chromophores. Slabs were prepared to mimic lesions of different depths. The optical properties of the tissue phantoms were determined in the visible and near-infrared spectral ranges using a noninvasive instrument made from a purpose-modified digital camera. The measured reflectance was correlated with the depth of the lesion both in a Monte Carlo simulation environment and in a laboratory experiment.