Research on the biomechanical behavior of soft tissues has drawn a lot of recent attention due to its application in tissue evaluation, early cancer detection, rehabilitation and surgery. Dynamic analysis of soft tissues not only provides histological, pathological and physiological information of the tissues, but also presents theoretical support for the modern medical imaging modalities (like Acoustic Radiation Force Imaging, Harmonic Motion Imaging, Supersonic Shear Imaging and Shear Wave Elasticity Imaging) based on tissue dynamics. Using our FEMSS (Finite Element Method with a State Space representation) technique, a realistic model of breast soft tissue with hard inclusions is geometrically discretized in ANSYS using finite elements, while a state space representation is adopted to characterize the motions of tissues stimulated by an internal radiation force. Our objective for this paper is to investigate the effects of size, location and mechanical properties of hard inclusions on the tissues’ response, frequency spectrum and forced vibration. The response differentiation between soft tissues with and without hard inclusions may reveal the resolution and delectability of the dynamic measurement and could lead in the development of new, more effective diagnostic techniques. Our simulation results indicate that the existence of hard inclusion(s) can significantly change the dynamic response of the tissue system. Specifically, hard inclusions may shift the spectrum of an elastic tissue system to a range of higher frequency, with larger sized hard inclusions causing bigger shifts. Furthermore, the location effect of hard inclusions is exhibited when a shallow one tends to vibrate with a larger magnitude at lower frequency than a deep hard inclusion. Finally, the tissue viscosity can significantly compress the range of high frequencies in the tissue system spectrum and cause the magnitude decrease of the forced vibration.

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