Determination of the nonlinearity parameter B/A of biological media.

The nonlinearity parameter B/A has been determined for various biological solutions and soft tissues using the thermodynamic and finite amplitude methods. Agreement between the two methods is better than 10% for the tissues and 1% for the solutions. Fat has a B/A value around 11, the highest among soft tissues studied. Other soft tissues including liver, muscle, brain, and heart muscle have B/A values close to 7. Based on the observed linear relation between the B/A value and solute concentration in protein solutions, and also the lack of dependence of the B/A value on solute molecular weight in dextran solutions, it is postulated that the nonlinearity in these solutions is due to solute-solvent interactions. The general trend of increasing B/A value with specimen structural hierarchy suggests that the nonlinearity of biological materials is related to this feature. These observations suggest the use of the nonlinearity parameter B/A in tissue characterization, particularly since structural alteration often attends the pathological state.