Nonlinear acoustics and biological media

Abstract

The propagation of nonlinear ultrasonic waves in aqueous solutions of biological macromolecules (tissue models) has been studied by making measurements of the fundamental at the sound source and the second harmonic as a function of distance from the source. These studies show that the nonlinearity parameter B/A for bovine serum albumin and hemoglobin solutions increases nearly linearly with concentration from 5.2 for water to 7.3 for a 40% solution, suggesting that the solution becomes more nonlinear as the spacing distance between molecules decreases. Solutions of dextran molecules also have been studied from the monomer to a molecular weight of 2 000 000 Daltons showing that the nonlinearity parameter, for fixed concentration, is relatively insensitive to molecular weight. Measurements have also been made in whole mammalian blood which exhibits a nonlinearity parameter in proportion to its dry weight which consists largely of protein. These findings suggest that details of nonlinear acoustic propagation in living systems may contribute to further improvement in clinical diagnostic procedures. [This research was supported by a grant from the National Science Foundation.]