Research On Phase Distortion Apactive Correction Technology Of Synthetic Aperture Ultrasonic Imaging Signal

Ultrasonic Synthetic Aperture Focusing Technology is the result of that nondestructive testing researchers have applied synthetic aperture radar(SAR)to ultrasound imaging.Ultrasound has significant advantages,such as strong penetration,good propagation direction,there is no clear diffraction,fast and efficient,so favored.However,when the ultrasonic wave propagates in the non-homogeneous media,the difference in velocity will introduce the wave-front error.The fine structure particles inside the material will produce reflective clutter,so that the received signal carries noise.And the sound wave attenuation occurs during propagation,the surface ups and downs of the material(I.e.,uneven)and diffraction,this series of factors will cause that the ultrasound image carries phase distortion,and thus image resolution is low.In order to solve the problem of phase distortion and improve the resolution of the image,this thesis will study the phase distortion and correction.Firstly,this thesis introduces four kinds of ultrasonic synthesis focusing imaging methods and their respective advantages and disadvantages,and chooses the synthetic focusing method among them.Simultaneously,using the direction of the DOA window function to eliminate the impact that is within ultrasonic signals caused by ultrasonic direction angle,so as to achieve the purpose of optimizing the imaging results.Then,the generation of phase distortion in ultrasonic synthesis focusing signal is described in detail,and its characteristic is analyzed in order to establish the mathematical model,and the computer is used to simulate the phase screen.The common phase distortion correction method is based on the cross correlation coefficient.Lots of adaptive cross-correlation phase correction methods can be derived from the traditional adjacent cross correlation correction method.In this thesis,an improved adaptive cross correlation phase correction method is researched to solve the optimization problem.Finally,use computer to simulate different defects and medical cyst tissue and add the phase screen,the adaptive and improved adaptive adjacent cross correlation phase distortion correction methods are used to process the simulation data with phase difference,and the images are obtained by synthetic aperture focused ultrasound imaging method.For single and two points simulation results,the image resolution after phase correction is increased in the range of 2.5%-10.9%than that before correction;for the multi-point simulation results,the peak signal-to-noise ratio of improved adaptive correction image is increased by 11.1%than the adaptive phase correction image before correction;for the cyst tissue simulation results,the image contrast noise ratio of phase correction images is increased in the range of 23.9%?52.7%than that with phase error,thus it could be proved that the adaptive method for phase difference correction is feasible and effective.In addition,collecting the actual data through Multi2000 ultrasound experimental platform,and the signal with phase distortion is obtained.Similarly,using adaptive and improved adjacent cross-correlation phase distortion correction method to process the raw data,and obtain synthetic aperture ultrasonic image.For the single and multi-point experimental data,image resolution after phase correction is increased in the range of 9.1%?17.1%than that before correction,so the feasibility and effectiveness of the phase correction algorithm are verified once again.