Research On Shear Wave Velocity Estimation Method For Ultrasonic Elastography

The evaluation of the physiological and pathological state of the human soft tissue by its hardness(elasticity)characteristics is one of the hot spots in the development of medical ultrasound.Ultrasonic elastography based on shear wave velocity to estimate the elasticity information of the media is an important detection method,and accurate estimation of shear wave velocity is the key to this technology.Aiming at the problems in the commonly used time-of-flight algorithm,this thesis studies the estimation methods of shear wave velocity.The research contents of this thesis are as follows:(1)Compared with the time-of-flight algorithm,the shear wave flight displacement is studied.The flight displacement algorithm is theoretically proposed to estimate the shear wave velocity in the homogeneous region of the ultrasound phantom,and is compared and analyzed with time-of-flight algorithm(axial displacement algorithm and axial velocity algorithm).The principle of axial displacement algorithm and axial velocity algorithm is discussed,and the estimation method of shear wave propagation period and wavelength in homogeneous region is studied.(2)The real-time propagation trajectory of shear wave is studied.In theory,a real-time curve tracing method of shear wave propagation trajectory by curve fitting to the state of shear wave trajectory is proposed.On the one hand,the accuracy and anti-noise performance of the method are studied;on the other hand,the effect of this method on the tracking of shear waves in the homogeneous and heterogeneous regions of the ultrasound phantom is studied;In addition,this method is used for ultrasonic elastography studies to reconstruct two-dimensional shear wave velocity maps and ultrasonic elastic maps of homogeneous and heterogeneous regions,respectively.The reconstruction quality of this method is evaluated by analyzing parameters such as wave velocity,relative error and signal-to-noise ratio in the region of interest.(3)According to the shape of the trajectory of the shear wave in the homogeneous region of the ultrasound phantom,the moving process of the centroid ordinate of the trajectory in the axial direction is studied,and the centroid longitudinal coordinate method for calculating the wave velocity is proposed,and this method is used to estimate the shear wave velocity in the homogeneous region of the two ultrasound phantoms.The results show that:(1)the proposed flight displacement algorithm is not only simple and highly stable,but also can obtain a velocity estimate closer to the true value;(2)the proposed curve tracking method can track the trajectory of the shear wave in real time,and this method has high accuracy and strong anti-noise performance.In addition,the two-dimensional shear wave velocity map and ultrasonic elasticity map reconstructed based on this method have accurate results and high signal-to-noise ratio.(3)The centroid longitudinal coordinate method can quickly and easily estimate the shear wave velocity in the homogeneous region,and the accuracy of the evaluation is higher than the axial displacement algorithm.Therefore,the methods proposed in this thesis can improve the accuracy of wave velocity estimation and provide new evaluation methods and reference schemes for the estimation of wave velocity in ultrasonic shear wave elastography.