The use of angular acoustic scattering measurements to estimate structural parameters of human and animal tissues

Theoretical formulations are developed, based on mathematical models of inhomogeneous continua for the expected angular variation of bulk scattering from human and animal tissues. These results are compared with experimental data on angular scattering from liver, muscle, and blood, reported in a companion paper [J. Acoust. Soc. Am. 79, 2034-2047 (1986)], and deductions are drawn as to the appropriateness of the various models for representing the mechanical structure of the different tissues. On this basis, the experimental data and theoretical formulations are used to derive estimates, appropriate to the frequency range of observation (4-7 MHz), of correlation distance (or effective scatterer spacing) d, the local variabilities of density and compressibility, gamma rho = delta rho/rho and gamma kappa = delta kappa/kappa 0, and their ratio gamma rho/gamma kappa. For blood, liver, and skeletal muscle, the values derived at 6 MHz for d are approximately 5, 55, and 75 microns and for gamma rho/gamma kappa are 0.5, 0.15, and 0.28, respectively. These results are, in particular, at variance with the commonly made assumption, based on evidence from low-frequency measurements, that the ratio gamma rho/gamma kappa is sufficiently small that density terms can be ignored in calculations of human tissue scattering.