NUMERICAL SIMULATION OF THE FIELD OF SECONDARY SOURCES THE ACOUSTIC WAVE WHEN PASSING THROUGH THE BIOLOGICAL ENVIRONMENT
N.N. Chernov, N.P. Zagray, M.V. Laguta, A.Y. Varenikova
The paper gives the substantiation of the relevance of the use of nonlinearity of biological tissues in the development of methods of ultrasonic visualization of internal structures. The equations underlying the interaction of an acoustic wave with a nonlinear biological medium are considered. As the basic equation describing the passage of an acoustic wave, the equation of a simple wave was accepted. It was chosen due to the fact that at small distances, about ten centimeters attenuation of the acoustic signal is not considered. The paper gives its description and boundary conditions. On its basis, an equation describing the field of secondary sources inside a heterogeneous biological medium consisting of several layers with different values of the nonlinear parameter is obtained. As a parameter of the acoustic wave, on the basis of which the restoration of the distribution of the nonlinear parameter of biotissue can be carried out, the vibrational velocity was chosen. A numerical simulation of the distribution of the amplitude values of the oscillatory velocity field of the second harmonic wave for this medium is carried out. The calculations used a three-dimensional coordinate system. For the convenience of calculations and presentation of the results, the thickness of the biological heterogeneous tissue was minimized relative to the z coordinate. the results of the calculations are presented in the form of a matrix of the distribution of the values of the vibrational velocity in the plane. The analysis of the obtained results of numerical simulation is carried out.
Keywords: ultrasound imaging, tomography, nonlinear parameter, field of secondary sources.