THE APPLICATION OF THE RELATIVE ACOUSTIC NONLINEAR PARAMETER FOR THE DEVELOPMENT OF BIOLOGICAL TISSUE IMAGING SYSTEMS
The paper discusses the issues of developing a method for visualizing the internal structures of the body, based on the restoration of the acoustic nonlinear parameter distribution. The process of occurrence and propagation of the second harmonic wave in tissues with high nonlinearity and attenuation is considered. The use of the relative acoustic nonlinear parameter in relation to the absolute nonlinear parameter of the medium is proposed. To solve the problem of restoring the distribution of the relative acoustic nonlinear parameter in biological media, an equation is obtained that eliminates the necessity to measure changes in absolute pressure values for both the fundamental frequency wave and its second harmonic. Mathematical expressions are derived that enable accounting for the attenuation processes for the fundamental frequency and for its second harmonic, taking into consideration the influence of the medium in which the object under study is placed. Expressions for determining the relative acoustic nonlinear parameter are acquired. Drawing on these expressions, the construction of a visualization system, utilizing algorithms for restoring the distribution of the acoustic nonlinear parameter in the cross section of a biological object, is presented. The main advantage of these equations is that there is no need to identify changes in the absolute amplitudes of the fundamental frequency and second harmonic waves. The outlined methods for calculating the nonlinear characteristics of biological tissues make it possible to simplify the technical implementation of ultrasound imaging systems.