Photothermal Radiometry for Skin Research

Abstract

Photothermal radiometry is an infrared remote sensing technique that has been used for skin and skin appendages research, in the areas of skin hydration, hydration gradient, skin hydration depth profiling, skin thickness measurements, skin pigmentation measurements, effect of topically applied substances, transdermal drug delivery, moisture content of bio-materials, membrane permeation, and nail and hair measurements. Compared with other technologies, photothermal radiometry has the advantages of non-contact, non-destructive, quick to make a measurement (a few seconds), and being spectroscopic in nature. It is also colour blind, and can work on any arbitrary sample surfaces. It has a unique depth profiling capability on a sample surface (typically the top 20 µm), which makes it particularly suitable for skin measurements. In this paper, we present a review of the photothermal radiometry work carried out in our research group. We will first introduce the theoretical background, then illustrate its applications with experimental results.

In Vivo Skin Characterizations by Using Opto-Thermal Depth-Resolved Detection Spectra

“…By analyzing the shape of the measured signal, we can get information on the sample's optical properties, thermal properties, the thickness of the sample, and its layer structure. The pulsed laser version, OTTER (opto-thermal transient emission radiometry), originally developed by Imhof et al [2,12,13] and subsequently by Xiao et al [13][14][15][16][17][18][19][20][21][22][23][24], has been intensively used for skin measurements. By using Nd:YAG Lasers (532 nm), skin melanin concentration (skin darkness) and skin hemoglobin concentration (i.e., blood distributions) can be measured [15][16][17][18], and by using Er:YAG Lasers (2.94 µm), skin hydration, skin hydration depth profiles, and skin topically applied substances can be measured [19][20][21][22][23][24].…”

In Vivo Human Hair Hydration Measurements by Using Opto-Thermal Radiometry

“…The closed chamber with a condenser makes it sure that every measurement is performed under the same condition, without the influence of external environment. As a result, AquaFlux has better repeatability and accuracy than any other TEWL instruments [12]. All the hair samples used in this study are freshly cut from healthy volunteers, prior to the measurements.…”

“…But to date, there is no technologies can resolve water depth distribution in hair. Our previous studies show that it is also possible to measure the water content as well as the water depth profiles in hair by using Opto-thermal transient emission radiometry (OTTER) [11][12][13][14], and to measure desorption of hair by using condenser trans-epidermal water loss (TEWL) method [15][16][17]. In this paper, we will present in vivo human hair hydration measurements by using OTTER.…”

Review of Modern Techniques for the Assessment of Skin Hydration

“…Initial experimentation was introduced by Imhof et al [96,97] followed by Xiao et al [98], and has been applied in a range of skin measurements including SC water content [99][100][101][102], pigmentation (particularly port wine stains) [103][104][105], nails [106], solvent penetration [107,108], and computational modelling of skin [109][110][111]. A study on the water-keratin interaction in relation to free and bound water in the SC [99] correlated OTTER results with previous findings from Leveque et al [112], showing that the absorption band of bound water at low humidity shifted towards high wavelengths, and was narrower than the band associated with bulk water.…”