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A Comparative Study of Photoacoustic and Reflectance Methods for Determination of Epidermal Melanin Content
 

Summary: A Comparative Study of Photoacoustic and Reflectance
Methods for Determination of Epidermal Melanin Content
John A. Viator,√w Jason Komadina,z Lars O. Svaasand,wy Guillermo Aguilar,wz Bernard Choi,w and
J. Stuart Nelsonw
√Department 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 I≠VI
were tested using the photoacoustic probe and VRS. A plot of PAMI v. VRS showed a good linear fit with r2
ľ 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