The Velocity of Sound through Tissues and the Acoustic Impedance of Tissues

Abstract

The velocity of sound through various animal organ tissues and through living human tissues was measured, using an ultrasonic pulse method, at 1.25 and 2.5 Mc. The effect of anisotropy (fiber direction) on velocity was determined with beef muscle. Values obtained with the beam traversing the tissue perpendicularly to the long axis of the muscle bundles did not differ significantly from those found with the energy directed parallel with the muscle fibers. Velocity through living human tissues, consisting mostly of muscle, was measured by transmitting the ultrasound through various thicknesses of the arm, leg, and thigh. Specific gravities of the tissues were measured. The characteristic acoustic impedances, calculated from the density and velocity data, vary between 1.5 x 105 and 1.7 x 105 g./sq. cm./sec. The imaginary component of tissue impedance is calculated and found to be negligible at the frequencies at which these measurements are made.