Numerical Simulation Of Acoustic Field In Focal Region Formed By High Intensity Focused Ultrasound

Objective:In this research we study the influence of different human tissues, different structure of the human tissues, different focused approach and different element excitation function on the acoustic field in focal region that formed by high-intensity focused ultrasound. Provide the theoretical methods and theory for the make of treatment plan and use the simulation results to guide the clinical therapy.Methods:We use the FDTD simulation method that introduced by Nagayoshi Morita to simulate the the process of high-intensity focused ultrasound nonlinear propagation, and utilized the property of cylindrical coordinate system to simulate the process of the ultrasound in water and single human tissue which is axial symmetry in two direction, for the human tissue that is not axial symmetry simulate the acoustic field in three directions. We also used Reichenberger's ESWL experiment in water as an example to build the simulation model to study the acoustic field when excitation function are different. Then we discuss the influence of different affecting factors on energy density in shallow region of the simulation model that build according to Reichenberger's ESWL experiment setup in phase controlled circle focusing, At last we study the acoustic field in focal region at the condition of human tissue is not perpendicular to ultrasonic transducer axis.Results:(1) In the same simulation model, when the ultrasound transducer was excited by different element excitation function, the size of the focal region, the pressure distribution in focal region and the focal length all changed.(2) At the condition of phase controlled circle focusing, change the length that from the circle to ultrasound transducer or the diameter of the circle, energy density distribution can be changed in shallow region that from the transducer more than 6cm, but the energy density distribution can not be changed when change the diameter of the ultrasound transducer.(3) When ultrasonic transducer axis is not perpendicular to human tissue, at the condition of the angle that they formed is less than 90°, the less the angle is the larger will the focus shift in radial direction, and the direction the focus moved to is different when in different human tissues. Conclusion:We use the FDTD simulation method that introduced by Nagayoshi Morita studied the influence of different element excitation function on the pressure distribution in focal region, the influence of different p in phase controlled circle focusing on energy density distribution in shallow region provided theory for the make of HIFU therapy plan, and build the simulation model in which human tissue that is not axial symmetry to study the acoustic field in focal region, established simplified and effective simulation model and simulation program.