Imaging of port wine stain lesions using a multi-sensor photoacoustic probe

Successful treatment of port wine stain (PWS) birthmarks in human skin utilizes cryogen spray cooling (CSC) in conjunction with laser treatment. CSC pre-cools the epidermis to protect it from subsequent laser irradiation which raises the temperature of both the epidermis and the deeper PWS. As the epidermal temperature is depressed by cryogen, damage to the skin surface is minimized while the PWS reaches temperatures sufficient to permanently damage the lesion. In order to optimize cooling and laser heating dosages and to properly guide laser therapy, the spatial relationship of epidermal melanin and PWS must be known. Photoacoustic depth profiling of human skin uses low energy, nanosecond pulses of laser light to induce acoustic waves in optically absorbing media, such as blood and melanin. We used a 532 nm Nd:YAG laser to measure total epidermal melanin content in human skin, comparing the results with visible reflectance spectroscopy. Furthermore, we performed numerical simulations of photoacoustic generation in skin, showing that a hemisperical acoustic sensor array could be used to reconstruct the rete pattern of epidermal melanin in the basal layer. Finally, we built a hemispherical probe for use in future experiments for imaging of human skin.