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Model-Independent Quantification of Complex Shear Modulus via Speed and Attenuation of Surface Waves

Shear-wave elastography imaging has been commonly used in the literature to characterize shear-wave propagation in order to estimate shear modulus in soft tissues. Instead of bulk shear waves, waves in thin tissue structures such as the layers of skin or membranes of organs travel following surface wave characteristics. Biomechanical characterization of surface waves in the literature often utilized model-based approximations for propagation speed, thereby omitting the effects of surface wave attenuation. In this work, we propose a method to estimate complex shear modulus from surface waves using both phase velocity and attenuation. We demonstrate this to estimate complex shear modulus of the skin at four different locations in upper extremity. For this purpose, we induce surface waves using a piezoelectric shaker on the skin, actuated at 25 Hz. Surface waves are tracked with high-frame rate plane-wave imaging using a high-frequency L22-14v transducer. We found an average storage-to-loss moduli ratio of 1.10, indicating that the loss modulus plays a significant role for the characterization of the skin and thus should not be ignored as common in the literature.