Shear properties of mammalian tissues at low megahertz frequencies

Abstract

Rough values for the transverse-wave specific acoustic impedance Zs = Rs + jXs, transverse velocity of sound cs, and transverse absorption coefficient .alpha.s were measured for canine liver, kidney, muscle and packed red blood cells in the frequency range from 2-14 MHz at 25.degree. C. The ranges of the results are Rs = 700-3000 .OMEGA.mech/cm2, Xs = 400-4000 .OMEGA.mech/cm2, cs = 900-10,000 cm/s and .alpha.s = 2000-30,000 np/cm. The corresponding results for shear stiffness .mu.1 and viscosity .mu.2 are .mu.1 < 107 dyn/cm2 and .mu.2 = 4-30 centipoise. At these frequencies the viscosities are orders of magnitude less than those reported at 0.5-5 kHz. The low impedances (viscosities) correspond to low velocities and extremely high absorption coefficients for shear waves in tissue.