Analysis of skin recovery from mechanical indentation using diffuse lighting and digital imaging

Skin behaves as a viscoelastic material, having mechanical properties composed of elastic and fluid components. Upon indentation, the fibres are stretched and fluid displaced from the compressed region. The rate of recovery from this imprint is therefore dependent on the hydration and elasticity of the skin. A reliable measurement could be applied to the assessment of clinical conditions such as oedema, rare genetic disorders such as cutis laxa and the evaluation of the 'effective age' of skin in vivo. This paper describes a new approach to the non-invasive indentation technique and a novel method of analysis. A method is proposed that tracks the skin's recovery optically from an initial strain made using a mechanical indentor, diffuse side-lighting and a CCD video-capture device. Using the blue colour plane of the image it is possible to examine the surface topography only, and track the decay of the imprint over time. Two algorithms are discussed for the extraction of information on the skin's displacement and are analysed in terms of reliability and reproducibility.