Shear properties of mammalian tissues at low megahertz frequencies

Rough values for the transverse-wave specific acoustic impedance Zs=Rs+jXs, transverse velocity of sound cs, and transverse absorption coefficient αs have been measured for canine liver, kidney, muscle tissues, and for packed red blood cells in the frequency range from 2 to 14 MHz at 25°C. The ranges of the results are Rs=700–3000 Ωmech/cm2, Xs=400–4000 Ωmech/cm2, cs=900–10 000 cm/sec, and αs=2000–30 000 np/cm. The corresponding results for shear stiffness μ1 and viscosity μ2 are μ1107 dyn/cm2 and μ2=4–30 centipoise. At these frequencies the viscosities are orders of magnitude less than those reported at 0.5–5 kHz by Oestreicher (1951). The low impedances (viscosities) correspond to low velocities and extremely high absorption coefficients for shear waves in tissue. Subject Classification: 4380.20, 4380.30.