Ultrasound Elastography of the Skin and Subcutis under Surface Extensive Loading

Measurement of skin elasticity has the potential to aid clinical diagnosis of a range of skin conditions. Our eventual goal is to develop an ultrasonic method for imaging the elasticity of the skin and subcutaneous tissue, and to use this technique to study skin cancer and lymphoedema. The aim of the present study was to investigate the effects of surface extensive loading, of varying direction, on the strain generated within normal skin and the underlying tissue layers. Extensive strains were applied to the surface of normal skin, while measuring the load and acquiring a sequence of ultrasound B-mode images. Correlation-based displacement tracking was used to generate displacement images from the ultrasound images. Least squares strain estimation then formed strain images, known as elastograms, of field size 18 mm (depth) by 28 mm (width). Propagation of strain into the subcutis was observed, suggesting that the technique could be useful in studying lymphoedema. Less strain was generated in underlying muscle. Confirmation of a previously observed anisotropy was obtained, as a modulation factor of about two and a periodicity of 90°, for the variation of stiffness with direction of loading.