The Research On Patterns Of Acoustic Radiation Forces In SSI Technique

Nowadays, acoustic radiation force-based elastography as non-invasive method of mechanical properties evaluation of biological tissues, which provides characterization of human tissue elasticity and viscosity for the clinical diagnosis and offers new information on morphological imaging, has great potential and vast development prospects. In the numerous research achievements, Supersonic Shear-wave Imaging (SSI), hereinafter referred to as SSI, the technological innovation on the way that acoustic radiation force applied— quickly apply ultrasound radiation force impulse at different depths to form a mach cone shear wave propagation, reducing the radiation dose, and achieving faster imaging speed.In acoustic radiation force-based elastography technique, the researches on how to generate radiation force, how ultrasound interact with tissues, as well as what kind of exciting radiation force sequence should be applied, are all fundamental and important. Therefore, this thesis performed some research works as follows.Based on the knowledge of acoustic theory and mechanics of materials, this thesis studied the process of ultrasound emission, the phenomenon of acoustic radiation force in ultrasonic attenuating tissue, and the generation of shear waves under the effect of acoustic radiation force. By combining Field II ultrasound field simulation method and the Green's function viscoelastic mechanics simulation method, the thesis established a model to simulate the particle displacement field of viscoelastic body under effect of fasted-moved, multi-focal focused ultrasound radiation force. Having taken advantage of the image of particle displacement field along the propagation of shear wave required by SSI, the compliance of this model is validated. Then the research on how to apply acoustic radiation force has been done through simulation. And further discussions on the Mach number, the span of radiation force, as well as transmitting aperture were conducted. This thesis proposed an idea on application of dynamic aperture for focused ultrasound emitting to generate radiation force.This thesis, based on the works of theoretical research, designed and implemented fast-moved, multi-focal, dynamic radiation force focused ultrasound emission system. In this system, control command is launched through the PC. FPGA receives the command and field configure the relevant emission mode, and drives 64 the linear array or convex array to emit the ultrasound focusing on any location on the acoustic axis at arbitrary duration and intervals with the set frequency.