Radiation impedance of a finite circular piston vibrating normal to an isotropic viscoelastic half-space with application to medical diagnosis

Abstract

In a recent study [J. Acoust. Soc. Am. 106, 3678–3686 (1999)], a new analytical solution was developed and validated experimentally for the problem of surface wave generation on a linear viscoelastic half-space by a rigid circular disk located on the surface and oscillating normal to it. The results of that study suggested that, for the low audible frequency range, some previously reported values of shear viscosity for soft biological tissues may be inaccurate. Those values were determined by matching radiation impedance measurements with theoretical calculations reported previously [J. Acoust. Soc. Am. 23, 707–714 (1951)]. In the current study, the new derivation is extended to the calculation of radiation impedance. Comparisons are made with prior theory and experiments to determine which theory is more accurate and what range of values for shear viscosity is more accurate. Measurement of skin surface radiation impedance has been studied by a few researchers for rapid, nonintrusive diagnosis of a variety of specific medical ailments. It is hoped that the developments reported here will advance these techniques and also provide insight into related diagnostic methods, such as sonoelastic imaging and other methodologies that utilize disease-related variations in soft tissue viscoelastic properties. [Work supported by a grant from the Whitaker Foundation.]