Elasticity of artificial skin by measuring displacement induced by acoustic radiation force

Wrinkled skin and sagging skin are closely related to both quantity and quality of collagen inside the dermis. Quantitative measurement of human skin elasticity is important because more interests are paid to skin aging in developed countries. The objectives of the present study are to generate micro-displacement of layered structure of artificial skin by acoustic radiation force (ARF) and to measure the displacement by phase analysis of high frequency ultrasound. A hemispherical PZT transducer with the central frequency of 1-MHz and the diameter of 30-mm was used as the applicator of ARF and a concave PVDF transducer with the central frequency of 100-MHz and the diameter of 4-mm was used as the sensor. Tone-burst pulse with the duration of 100 μsec was input to the applicator. A time interval of Tone-burst pulse is 1000 μsec. The relaxation time of living tissues is considered the order of a few seconds. The time interval is much smaller than the relaxation time. The pulse was synchronized with 100 MHz ultrasound of 3000 Hz repetition rate. With the position of the transducer fixed, the ultrasonic reflection was digitized with 1-GHz sampling and the RF signals were acquired at a 3000 Hz repetition rate. Obtained RF signal of scanning line was converted to M-mode image by a conventional image processing algorithm of echography. Strain of each layer was calculated by the displacement speed of each layer. The value of the collagen sponge layer is the highest, that of the silicone layer is the second and that of the mesh layer is the lowest. The method is applicable for in vivo elasticity measurement and it would provide significant information in human skin aging.