Theoretical and experimental study of the third-order nonlinearity parameter C/A for biological media

The third-order nonlinearity parameter C/A for biological media is studied theoretically and experimentally. Based on the theory of fluid dynamics, the generalized Burgers equation is extended to the third order for biological media. A perturbation solution of the equation is carried out and the formula for C/A for biological media is derived. The sound pressure of the third harmonics changing with distance in water is measured and compared with the theoretical results. An experimental set-up is established for measurement of C/A for biological media and the values of the acoustic nonlinearity parameter C/A are measured for several porcine samples. The results show that the values of C/A for the measured biological tissues are in the range of 60.0–120.0 while the values B/A for the measured biological tissues are in the range 6.5–11.0. The maximum relative deviation for C/A among the measured biological tissues is 81.2% while it is only 66.2% for B/A. Therefore, C/A may be more appropriate for tissue characterization compared with B/A.