Two-dimensional Ultrasonic Viscoelastic Imaging Method Based On Low-frequency Vibration

Ultrasound elastography produces vibration in human tissues by stimulation and uses ultrasonic pulse-echo technology to detect the vibration information which can be applied to extract and imaging tissue viscoelastic information.In recent years,this technology has developed rapidly.For example,acoustic radiation force pulse imaging and transient elastography have been applied for the non-invasive diagnosis of liver diseases.However,these techniques still need to be improved in the diagnostic accuracy.In particular,for relatively obese patients,these techniques often fail due to the limited detection depth.On the basis of summarizing the limitation of the existing elastography technologies,this paper proposes a two-dimensional ultrasound viscoelastic imaging method based on low-frequency vibration,which can rapidly image tissue viscoelasticity in a deeper and larger range.This method uses a loudspeaker as an excitation source to generate higher-amplitude shear-wave vibrations within the tissue in order to obtain reliable estimates of shear-wave velocity in deeper tissues.The method uses ultrafast imaging based on plane wave to detect the shear wave,calculates the shear wave velocity value by processing the ultrasonic echo signal,and applies a biomechanical model to fit the dispersion curve to obtain the viscoelasticity.The work of this paper is divided into three parts:finite element simulation,experimental platform construction and imaging experiment.The finite element simulation part created a shear wave horizontal propagation model and a shear wave multi-angle propagation model,and simulated the shear wave velocity estimation under the condition that a hard block material and a uniform material.The results show that the method proposed in this paper can effectively distinguish hard block areas and provide empirical parameters for later experiments.In the experiment platform construction part,an imaging experiment platform based on Verasonics was built,and an imaging algorithm was implemented based on the platform.In the imaging experiment part,the standard elastic phantom and the pig liver sample were tested.Furthermore,the method of this paper was compared with the acoustic radiation force pulse imaging.It was found that in the region of interest of 52mm(170 wavelength)from the depth of the probe,this method produced a higher amplitude shear wave,which can effectively track the propagation process of shear wave.In comparison,the excitation pulse energy of the acoustic radiation force cannot reach the depth,and the effective shear wave propagation cannot be detected.The experimental results show that the method in this paper can rapidly obtain elastography image in a deeper and larger range,and can also obtain viscoelasticity at the same time,which can provide more useful information for the clinics.