CALCULATION OF THE REFLECTION AND TRANSMISION COEFICIENTS OF A PLANE ULTRASONIC WAVE THROUGH A LAYER OF DISSIPATIVE BIOLOGICAL TISSUE

Abstract

Background. Investigation of propagation of an ultrasound wave through layers of dissipative biological tissues along with theoretical interest has also a practical meaning in ultrasound therapy and diagnostics. It is well known that the result of the ultrasound therapeutic effect and the quality of ultrasound imaging depend on the fraction of ultrasound energy absorbed in the material of a tissue. Dissipation of acoustic energy leads to a thermal bio-effect and lowers a contrast of images received by ultrasound scanners.Objectives. We wanted to calculate the coefficients of transmission and reflection of a plane ultrasonic wave through a layer of dissipative biological tissue during the normal incidence of the wave on the surface of that layer.Materials and methods. The normal incidence of a plane ultrasonic wave on the layer of dissipative tissue was considered. Taking into account the continuity conditions for pressure and velocity in the ultrasonic wave at two boundaries of the tissue’s layer, the expressions for the reflection and transmission coefficients were obtained.Results. The explicit expressions for values of both coefficients in case of a normal incidence of ultrasonic wave were obtained and the parameters defining the magnitudes of these coefficients were determined. Namely, the relative acoustic impedances of the media through which ultrasonic wave propagates, the coefficient of absorption in the layer of a tissue, and the frequency of ultrasound.Conclusions. The results of this work allow calculating therapeutic effects produced by the ultrasonic wave. Particularly, they can be used for estimation of the intensity of the ultrasound wave in the human’s internal organs during non-invasive ultrasound interventions and the magnitude of temperature increase in the area of ultrasound irradiation. These results may be used for calculations of a therapeutic action of ultrasound wave, numerical simulations of the propagation of ultrasound wave through multilayered biological structures for improvement of ultrasound visualization of organs. Also, they can be used for improvement in the effectiveness in ultrasound applications, and for estimation of the magnitude of undesirable ultrasound side effects during diagnostic ultrasound screening.