Viscoelastic anisotropy in porcine skin: acousto-optical and mechanical measurements (Invited Paper)

Abstract

The anisotropic nature of the mechanical loss factor, tan u, ofex vivo porcine skin was evaluated using a novel acousto-optical method as well as by more tranditional dynamic mechanical testing. The acousto-optical method called acousto-optical elastography (AOE) relies upon launching low frequency (0.5Hz) acoustic stress waves into the skin with an acoustic speaker and quantifying the displacement ofthe skin surface by tracking a backscattered laser speckle pattern with a linear array CCD camera. Two different optical wavelengths were used to monitor the surface acoustic waves, 543 nm and 633 nm. The 633 nm light has a penetration depth on the order of 3 times that of the 543 nm light. The value of tan δ was found to be dependent upon the orientation in which the skin samples were tested. For both the AOE employing 543nm light and the dynamic mechanical testing approaches, tan δ was greatest in the dorso-ventral direction and smallest in the cranial caudal direction. The actual values of tan δ were significantly greater when they were determined using traditional mechanical testing than with the AOE method. This was attributed to the greater strain range over which tan δ was calculated when using dynamic mechanical testing. The AOE method using the 633 nm light provided data not only on the skin, but the underlying tissue as well, masking the anisotropic behavior of the porcine skin. The results of this study indicate that AOE may be a suitable testing method for quantifying aspects of mechanical behavior of tissues in vivo.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.