title: A comparative study of photoacoustic and reflectance methods for determination of epidermal melanin content.
abstract: Although epidermal melanin content has been quantified non-invasively using visible reflectance spectroscopy (VRS), there is currently no way to determine melanin distribution in the epidermis. We have developed a photoacoustic probe that uses a Q-switched, frequency-doubled Nd:YAG (neodymium, yttrium, aluminum, garnet) laser operating at 532 nm to generate acoustic pulses in skin in vivo. The probe contained a piezoelectric element that detected photoacoustic waves that were then analyzed for epidermal melanin content using a photoacoustic melanin index (PAMI). Melanin content was compared between results of photoacoustics and VRS. Spectra from human skin were fitted to a model based on diffusion theory that included parameters for epidermal thickness, melanin content, hair color and density, and dermal blood content. Ten human subjects with skin phototypes I-VI were tested using the photoacoustic probe and VRS. A plot of PAMI v. VRS showed a good linear fit with r2=0.85. Photoacoustic and VRS measurements are shown for a human subject with vitiligo, indicating that melanin was almost completely absent. We present preliminary modeling for photoacoustic probe design and analysis necessary for depth profiling of epidermal melanin.
authors.affiliation: Department of Dermatology, Oregon Health & Science University, Portland, Oregon 97239, USA. viatorj@ohsu.edu
authors.forename: John A
authors.initials: JA
authors.lastname: Viator
authors.forename: Jason
authors.initials: J
authors.lastname: Komadina
authors.forename: Lars O
authors.initials: LO
authors.lastname: Svaasand
authors.forename: Guillermo
authors.initials: G
authors.lastname: Aguilar
authors.forename: Bernard
authors.initials: B
authors.lastname: Choi
authors.forename: J
authors.initials: J
authors.lastname: Stuart Nelson
mesh_terms: D000162:Acoustics; D004817:Epidermis / Q000378:metabolism*; D006400:Hematocrit; D006454:Hemoglobins; D006801:Humans; D007834:Lasers; D008543:Melanins / Q000378:metabolism*; D013057:Spectrum Analysis; D014820:Vitiligo / Q000175:diagnosis*
chemical_list: D006454:Hemoglobins; D008543:Melanins