In vivo evaluation and imaging of skin elasticity applying high frequency (22 MHz) ultrasound

The assessment of skin elasticity as a method to investigate effects of skin ageing, sun exposure and pathological conditions is of greatest interest in dermatology. In this paper a new technique for the evaluation and imaging of skin elasticity in vivo applying ultrasound in the 20 MHz range is presented. In our approach we acquire rf echo signal frames under stepwise increasing negative pressure applied to the skin surface that causes suction. A computer controlled vacuum system with a digital pressure control loop is used for precise and reproducible results. The resulting deformation of the skin surface is analyzed by threshold based segmentation with a nonlinear approach for hair echo signal removal. Local axial strains in the epidermis and dermis are calculated from consecutive rf echo signal frames applying the ´phase root seeking´ algorithm. We use the correlation coefficient of windowed and time shift compensated echo signals as a measure for the reliability of the estimated strains. Elastic properties of the subcutaneous fat are assessed analyzing tissue structure movements in B-mode frames. Results from phantom and in vivo measurements are presented. It is shown that strains in the epidermis, dermis and the subcutaneous fat are significantly different. Our results show that 20 MHz ultrasound based strain imaging is a potential tool for skin structures elasticity evaluation.