Near-infrared autofluorescence imaging of cutaneous melanins and human skin in vivo

Abstract

In recent years, near-infrared (NIR) autofluorescence imaging has been explored as a novel technique for tissue evaluation and diagnosis. We present an NIR fluorescence imaging system optimized for the dermatologic clinical setting, with particular utility for the direct characterization of cutaneous melanins in vivo. A 785-nm diode laser is coupled into a ring light guide to uniformly illuminate the skin. A bandpass filter is used to purify the laser light for fluorescence excitation, while a long-pass filter is used to block the main laser wavelength but pass the spontaneous components for NIR reflectance imaging. A computer-controlled filter holder is used to switch these two filters to select between reflectance and fluorescence imaging modes. Both the reflectance and fluorescence photons are collected by an NIR-sensitive charge-coupled device (CCD) camera to form the respective images. Preliminary results show that cutaneous melanin in pigmented skin disorders emits higher NIR autofluorescence than surrounding normal tissue. This confirmed our previous findings from NIR fluorescence spectroscopy study of cutaneous melanins and provides a new approach to directly image the distributions of cutaneous melanins in the skin. In-vivo NIR autofluorescence images may be useful for clinical evaluation and diagnosis of pigmented skin lesions, including melanoma.