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

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Abstract
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 differnet tissues. On the 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 variaiblities of density and compressibility, y.rho. = .DELTA..rho./.rho. and .gamma..kappa. = .DELTA..kappa./.kappa.O, 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 .mu.m 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.