Near-infrared autofluorescence spectroscopy and photobleaching detection of melanin-pigmented cutaneous neoplasia

In the current study, an excitation laser source emitting at 785 nm (100 mW, CW) was used to obtain ex vivo fluorescence of endogenous melanin in pigmented skin with benign, dysplastic and malignant cutaneous lesions. The samples were obtained after surgical removal during standard excision procedure and split for spectral analysis and histological verification. The samples of benign (BN-5) and dysplastic (DN-3) nevi and of malignant melanoma (MM-7) were used as representative for harmless/harmful cutaneous neoplasia with a similar melanin pigmentation. Emission in the range 800 – 1100 nm was detected and compared using a USB4000 micro-spectrometer (Ocean Optics Inc., USA). The photobleaching dynamics was observed for the emission maxima at 825 nm for 10 minutes with a step of 20 s. These near-IR autofluorescence spectra may be assigned to a single fluorophore if appropriate excitation wavelength is applied, which simplifies the rapid analysis related to the appearance and concentration evaluation of a given type of endogenous fluorophore, as well as allows the evaluation of some parameters, such as photobleaching dynamics, as a diagnostic indicator assessing the tissue state. A diagnostic accuracy of 93.3% was achieved for MM lesions validation when the NIR fluorescence intensity and photobleaching rate values were used to discriminate between nevi and melanoma lesions.