Determination of B/A of Biological Media by Measuring and Modeling Nonlinear Distortion of Pulsed Acoustic Wave in Two-Layer System of Media

Abstract

Knowledge of the acoustic nonlinearity parameter, B/A, of biological fluids or soft tissues is necessary whenever high intensity pressure fields are induced. A numerical model recently developed in our lab is capable of fast predicting the nonlinear distortion of pulsed finite-amplitude acoustic waves generated from axisymmetric sources propagating through multilayer attenuating media. Quantitative analysis of the obtained results enabled developing the alternative method for determination of the B/A of biological media. First, the method involves measuring the nonlinear waveform distortion of the tone burst propagating through water. Then, it involves numerical modeling (in frequency domain) using the Time-Averaged Wave Envelope (TAWE) approach. The numerical simulation results are fitted to the experimental data by adjusting the source boundary conditions to determine accurately the source pressure, effective radius and apodization function being the input parameters to the numerical solver. Next, the method involves measuring the nonlinear distortion of idem tone burst passing through the two-layer system of parallel media. Then, we numerically model nonlinear distortion in two-layer system of media in frequency domain under experimental boundary conditions. The numerical simulation results are fitted to the experimental data by adjusting the B/A value of the tested material. Values of the B/A for 1.3-butanediol at both the ambient (25^°C) and physiological (36.6^°C) temperatures were determined. The obtained result (B/A = 10.5 ± 5% at 25^°C) is in a good agreement with that available in literature. The B/A = 11.5 ± 5% at 36.6^°C was determined.