Influence Of Medium Properties And Nonlinear Effects On Ultrasound Focusing During HIFU Therapy

The focusing technique is the most important in HIFU therapysystem, and its effect determines success and safety of therapy. It hasvital significance for actual therapy to calculate and analyze the focalcharacteristics in every different condition. In this paper, the soundfocusing is studied from two sides after HIFU and equations of soundsummarized. Firstly, the influence of medium properties on sound.focusing has been studied with Rayleigh integral. Secondly, the influenceof sound nonlinear effect on sound focusing has been studied by solvingthe spheroidal beam equation. In addition, the relation of sound focusingwith distribution of tissue temperature in HIFU therapy is analyzedqualitatively with Pennes equation. The following main subjects areincluded in this paper.1. The sound field distribution equations are summarized, and thenonlinear acoustics is presented. Analyzing glancingly oraccurately to the second minuteness the linear and nonlinearequations of sound are gained. The development of nonlinearacoustics and its two classical equations, KZK equation and SBEequation are presented base for calculate sound field.2. To study the influence of medium properties on sound focusing,Rayleigh integral is adopted to study the self-focused concave spherical radiator. After simulating the distribution of soundpressure in every medium with different parameters such asattenuation coefficient, velocity of sound and temperature, theinfluence of every medium propertie on sound focusing iseduced.3. To study the influence of sound nonlinear effects on soundfocusing, the SBE equation brought forward by Kamakura isadopted to study the self-focused concave spherical radiator.After simulating the distribution of sound pressure of the firstthree harmonics generated by the nonlinear acoustical effectswhen the medium properties or the radiator parameters change,the influence of nonlinear effect on sound focusing is educed.4. The distribution of sound field and its influences on thedistribution of temperature during HIFU therapy are analyzedqualitatively. The results show that sound focusing is importantto therapy.