The Influence Of Ribs On The Propagation Of Strongly Focused High-intensity Nonlinear Ultrasound Beam

As a new ultrasonic application in medical field,High-intensity focused ultrasound(HIFU)has aroused general interest in recent years.In this paper,based on the spheroidal beam equation(SBE),a three-dimensional numerical algorithm is developed to solve the nonlinear acoustic field generated by a focused ultrasonic transducer with a large aperture angle.And the influence of ribs on the propagation of strongly focused high-intensity nonlinear ultrasound beam inside the body is studied.Moreover,a method based on Geometric Acoustic Approach has summarized to protect the rib.Chapter 1 is a brief introduction of the history and the progress of the us e of HIFU and the study of nonlinear ultrasound field focused by transducer.I n Chapter 2,we divide the Westervelt equation in detail from the fundamental fluid equation and use the Spheroidal Beam Equation(SBE)model and corres ponding numerical model to calculate the nonlinear ultrasound distribution in di rectional and lateral direction.The comparison of the focused ultrasound field generated by small-angle and wide-angle transducer is made to study the advan tages of strong focused field.And the influence of different radiation frequenci es and open holes in transducers on the ultrasound field is also proposed.The pressure field in layered tissue is simulated as well.In Chapter 3,a three-dim ensional numerical algorithm is developed to solve the nonlinear acoustic field generated by a focused ultrasonic transducer with a large aperture angle.Detail s about how to overcome the computational difficulty of numerical oscillations have been described,and the three dimensional model has been verified.In Ch apter 4,two rib configuration and different treatment depth have been discusse d to explore the influence of rib to the high focused nonlinear acoustic field.Chapter 5 gives more particular model with three tissue level,and a solution b ased on different f-number has been proposed.In Chapter 6,based on the Geo metric Acoustic Approach,the rib could be well protected and the energy besi de the rib has slightly influenced.In conclusion,in this paper,the physics mechanism of HIFU is deduced,and the strongly focused nonlinear ultrasound filed and corresponding heat deposition are discussed.It has mainly given a novelty the dimensional numerical model,it is proposed to study the application of HIFU in the use of cancer treatment with the rib in the propagation,which would give suggestions to the theoretical study and actual practice.