Research On Low Computational Complex Beamforming Algorithms In B-mode Medical Ultrasound Imaging

Beamforming algorithm is an important step in medical ultrasound system,which affects the quality of ultrasound image.The traditional delay and sum(DAS)beamforming is simple and easy to implement,which is widely used in the existing medical ultrasound system.However,the imaging results are suffered from low later resolution and high level side lobes.To address this problem,many new excellent algorithms have been proposed,which greatly improve the resolution and contrast of ultrasound imaging.Unfortunately,the improvement of its performance is at the cost of increasing computational complexity,which restricts its engineering application.Therefore,seeking for an innovation algorithm with better performance and lower complex to real-time imaging has become one hot issue in study of ultrasound beamforming.It is an important guarantee for improving the quality of medical ultrasound imaging equipment in our country and has great research significance and market value.In this thesis,to focus on this problem,based on different ultrasound imaging systems,taking the beamforming as the research object and reducing the computational complexity as the research main line,the in-depth and systematic research is carried out from four aspects.These four aspects include time domain,beam-space,plane wave and transform domain.Furthermore,corresponding characteristic beamforming algorithms with lower computational complexity are proposed.The main research works of this paper are as follows:1.Based on the time domain beamforming algorithm,sub-array average delay multiply and sum(SA-DMAS)beamforming algorithm is proposed.The algorithm is designed to reduce the computational complexity and improve the imaging performance of delay multiply and sum beamforming.Firstly,by reanalyze the delay multiply and sum beamforming,an equivalent expression with matrix as the minimum element is constructed.The matrix is composed of the covariance matrix of the echo signal.2-D echo data set firstly,which improves the imaging speed greatly.Then the results of sign coherent factor and DMAS beamforming for each transmitting are calculated,respectively.Furthermore,the auto-correlation components are introduced into the DMAS beamforming.Finally,based on the calculation results of the two,a plane wave beamforming model based on the 2D echo signal data-set is constructed.Due to the sign coherent factor is simple and easy realized by hardware,and the smallest computing unit is in matrix form,which can effectively reduce the computational complexity and improve the imaging speed(frame rate).The simulation is used to evaluate the performance of proposed method.Results show that,compared with the traditional plane wave imaging,the lateral resolution of SCF-DMAS beamforming improves greatly for the point targets,and for the cyst phantom,the contrast ratio(CR)and contrast-to-noise ratio(CNR)increased by 96.97%and by 79.98%respectively without reducing the frame rate.4.Based on the transform domain beamforming algorithm,a discrete cosine transform minimum variance beamforming(DCTMV)is proposed.This algorithm aims at reducing computational complexity without increasing hardware cost in transform domain beamforming.Firstly,the decimation cosine transform matrix is constructed.By using this matrix,not only the time domain signal is projected onto low-dimensional cosine transform domain,but also the properties of the time domain signal are preserved.Then,by means of the orthogonality of the decimation matrix,the minimum variance beamforming can be transplanted to the transform domain directly.Finally,the minimum variance beamforming is re-deduced,and the corresponding parallel processing model in the discrete cosine transform domain is established.Simulation and experimental results verify the effectiveness of the method.The results show that,compared with the minimum variance beamforming in time domain,the computational complexity is reduced fron O(L3)to O(PL2),at the same time,the resolution and contrast is improved.In addition,the proposed method is robust to noise.In summary,in this paper,in order to reduce the computational complexity and improve the quality of ultrasound imaging,the following attempts are made for the beamforming algorithms of different systems.One is to use the matrix as the minimum data processing unit.The second is to use the discrete cosine transform to compress the echo data.The third is to construct the decimation orthogonal transformation matrix to reduce the dimension.The corresponding beamforming method are established and verified by simulation and experiment.It has academic and practical value and provides technical and theoretical support for improvement of the quality of existing medical ultrasound imaging systems.