Research On The Image Quality Improments Of Medical Ultrasound Imaging Using Adaptive A Number Of Weighting Methods

Ultrasound imaging technique plays an important role in clinical diagnosis and is an irreplaceable medical imaging technique.Beamforming is an important part in the ultrasound imaging process,and directly determines the final reconstructed image quality.Although traditional delay and sum(DAS)beamformer can reconstruct ultrasound image quickly,it can not reduce clutter and noise effectively,and thus generate low-quality ultrasound image with poor resolution and contrast.Since adaptive beamforming techniques have the ability to obtain high quality ultrasound images,studies on adaptive beamforming in ultrasound imaging have been a hot research region in the past thirty years.This thesis focused on the study of adaptive beamforming method in ultrasound imaging,and proposed three novel adaptive beamforming methods for different medical ultrasound imaging modes to improve imaging quality,the specific contents are as follows:First,an adaptive weighting method named subarray difference factor(SDF)was proposed to overcome the problem of the influence of adaptive weighting factors on background speckle statistics.The proposed SDF is suitable for conventional focused ultrasound imaging,which applies the subarray smoothing on echo signals received by the transducer array to obtain mean values which can represent the intensity of high coherence components.Then,the differential operation is used to obtain the differences of the echo signals received by adjacent elements.Finally,SDF is used to weight the DAS output.Simulation and phantom experimental results indicate that SDF can enhance the imaging quality of background tissue and significantly improve the speckle signal-tonoise ratio.Secondly,this thesis proposed the sign coherence factor(SCF)as an adaptive weighting method to utilize the coherence information among plane waves with different angles to generate high quality ultrasound image effectively.In the SCF method,the imaging outputs of the same imaging point at plane waves with different angles are used to form a vector,and then utilized to calculate the SCF value.The imaging result of the imaging point using coherent plane wave compounding is used for weighting,and then get the final SCF-CPWC imaging result.Simulation and experimental results indicate that SCF-CPWC can achieve enhanced imaging quality compared with conventional CPWC imaging.Moreover,the proposed method can significantly enhance lateral resolution and contrast performances of cyst target.Finally,this thesis proposed a new weighting method by combining DAS beamforming and Fourier beamforming.Since delay-and-sum beamformer and Fourier beamformer both have their own distribution characteristics of side lobes,which distributed in horizonal and axial respectively.This thesis proposes a joint beamforming method for reduction of the two kinds of side lobe,which joints the delay-and-sum beamformer and Fourier beamformer.Simulation and experimental results indicate that the proposed method reduces the side lobes in DAS beamforming and Fourier beamforming effectively.As a result,the proposed method improves the dynamic range significantly,and enhances the ultrasound image quality.In summary,this thesis proposed several adaptive beamforming methods for the enhancement of ultrasound image quality.Simulation and experiments were conducted to verify the effectiveness of the proposed methods.The proposed methods in this thesis have some academic importance for improving ultrasound image quality and potential cinical diagnosis value.