Research On The Ultrasound Elasticity Imaging Based On Acoustic Radiation Force

To measure the tissue stiffness of human organs more accurately, ultrasoundelasticity imaging, a complementary method for B-mode ultrasound, has beendeveloped rapidly during less than20years and a variety of modalities have comeout. Among those, the most remarkable one is the acoustic radiation force basedelasticity imaging which has been developed in recent years. Compared with otherimaging modalities, it has become an important trend of future for its uniquefeatures of quantitation, deep detecting and high repeatability.This study is started from the research on impulsive acoustic radiation forceimaging, during which the functional relationship between the acoustic fieldproduced by ultrasonic probe and the radiation forces caused by this field arederived, and the simulation is realized by using FIELD II. At the same time, a finiteelement model of a tissue is built and the loading with boundary conditions for thesolving is discussed.In the aspect of1-D shear wave imaging, the estimate of the shear wave speedis carried out by placing lots of sign points along the shear wave propagationdirection, and recording the moments that the shear wave crest arrives at thosepoints, which is also called time-to-peak displacement method. The ultrasoundcross-correlation method is introduced to estimate the tissue displacements, to trackthe shear wave propagation, to calculate the shear wave speed, and finally to get thetissue stiffness, while the estimation accuracy is not good enough. To solve thisproblem, a deep analysis is made. By combining the advantages of support vectormachine interpolation method, a support vector regression based estimation methodis came up with and it is verified through simulation.Based on the1-D shear wave imaging,2-D shear wave imaging is alsoanalyzed, and the conditions needed to implement a full2-D imaging procedure arediscussed. By using this, continuous acoustic radiation forces are performed in bothisotropic model and anisotropic model respectively, forming two quasi-plane shearwaves. The displacement responses are observed and the shear wave speeds areestimated. Aiming at the matter of low accuracy for2-D shear wave speedestimation, some factors that can influence the estimation are discussed at the end ofthis dissertation.