Summary: A Comparative Study of Photoacoustic and Reflectance
Methods for Determination of Epidermal Melanin Content
John A. Viator,Ãw Jason Komadina,z Lars O. Svaasand,wy Guillermo Aguilar,wz Bernard Choi,w and
J. Stuart Nelsonw
ÃDepartment of Dermatology, Oregon Health & Science University, Portland, Oregon, USA; wBeckman Laser Institute, University of California, Irvine,
California, USA; zHarvey Mudd College, Claremont, California, USA; yNorwegian Institute of Technology, Division of Physical Electronics, University of
Trondheim, Trondheim, Norway; zDepartment of Mechanical Engineering, University of California, Riverside, California, USA
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 I­VI
were tested using the photoacoustic probe and VRS. A plot of PAMI v. VRS showed a good linear fit with r2
¼ 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.

Source: Aguilar, Guillermo - Department of Mechanical Engineering, University of California at Riverside

Collections: Engineering