Study On Beamforming Algorithm Of Synthetic Aperture Ultrasound Imaging

Synthetic aperture ultrasound imaging as a method of ultrasonic post-processing, can be synthesized as a small aperture forming a large aperture imaging, the imaging method can decrease the limit of the imaging resolution that depends on the imaging location and depth by focusing point by point. Thus, the imaging quality can be greatly improved compared with traditional ultrasound imaging methods.This article introduced one of the most important devices- ultrasound transducer firstly, and the basic theory of ultrasound imaging and the model for calculating the field profile from arbitrarily shaped transducers under continuous wave and pulsed excitation are discussed. A circular transducer impulse response of the acoustic pressure distribution was simulated with Field II, also a related experiment system was designed to validate.Secondly, the basic theory of the delay-and-sum beamforming is introduced, and the relationship between imaging dynamic range, spatial resolution and phase control accuracy, amplitude apodization, dynamic focus are discussed. Then the synthetic aperture imaging algorithms and beam scanning control technology has been researched, and some commonly used synthetic aperture imaging methods have been carried on the simulation experiment of the beam using Field II.Thirdly, adaptive beamforming algorithms are introduced, and a forward-backward minimum variance beamforming combined with coherence factor(CF+FBMV) algorithms is proposed. CF+FBMV algorithm: Firstly, Forward-backward minimum variance beamforming(FBMV) spatial averaging, instead of the conventional forward-only spatial averaging is used to obtain a more accurate covariance matrix; secondly, using the calculated optimum weight factor instead of the coherent sum in coherence factor, lastly, the factor is used to weight the results of FBMV beamforming. A series of point spread imaging and cyst phantom imaging using several common algorithms and CF+FBMV algorithm are displayed using Field II, the simulated result indicates that the proposed method in the aspects of imaging resolution, contrast and robustness are better than existed algorithms.Ultrasound imaging with plane wave coherent compounding technology was introduced, coherent compounding of multi-angle plane waves can improve the image quality. Then the CF+FBMV beamforming in ultrasound imaging with different number plane wave compounding has been simulated and compared.Lastly, using tungsten wires as the imaging object, Simulated the point target imaging using delay-and-sum beamforming algorithm in multi-element synthetic aperture focusing method on an FPGA-Based Open Platform for Ultrasound, verify that using the window apodization function can improve the quality of imaging compare with uniform apodization.