A comparative study of photoacoustic and reflectance methods for determination of epidermal melanin content.

John A Viator,Bernard Choi,Jason Komadina,Lars O Svaasand,Guillermo Aguilar,J Stuart Nelson

doi:10.1111/j.0022-202x.2004.22610.x

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.

Highlights

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
The complicated nature of the waveforms, which depart from the simple form of Fig 1, is due to the irregular distribution of epidermal melanin and the fact that the acoustic waves were integrated over the entire surface of the 200 mm active area of the polyvinylidene fluoride (PVDF)
VRS measurements Four VRS signals representing the same measurements of skin phototypes I-II, III, IV, and V-VI are shown in Fig 3 as solid lines

Summary

Introduction

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. The probe contained a piezoelectric element that detected photoacoustic waves that were analyzed for epidermal melanin content using a photoacoustic melanin index (PAMI). 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. 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

Objectives

Methods

Results

Conclusion