Improvement Of Shear Wave Velocity Measurement Method In Ultrasound Elastography

Non-invasive detection of biological tissue mechanical properties contributes to the early diagnosis of disease.Ultrasonic shear wave elastography(SWE)can quantitatively measure soft tissue viscoelasticity by estimating the local shear wave velocity of tissue.Time-to-peak(TTP)is the main method for measuring the shear wave velocity.The principle is to excite the local vibration of the tissue,which propagate outward in the form of shear wave,by acoustic radiation force.Then,the array element emits a short pulse to track the displacement of each detection point in the lateral direction,and finally estimates the shear wave propagation speed value according to the time at which the shear wave reaches the peak at the detection point.The pulse repetition frequency of the short pulse(fast signal)determines the sampling rate of the detection point displacement curve(slow signal).Affected by the propagation speed and depth of detection of ultrasound in the tissue,the upper limit of the sampling rate is less than 40 KHz.The shear wave velocity in the tissue with high stiffness is fast,and the sampling rate limitation cannot accurately distinguish the peak time of the shear wave at the adjacent detection point,thus causing measurement error.This research innovatively proposes an improved method based on multiple excitations for different phase acquisitions to improve the accuracy of wave velocity measurement.In this study,Triple Different Phase Modes(TDPMs)are taken as an example.The performance of this method is compared with the commonly used Single Push Mode(SPM)and Triple Same Push Mode(TSPM).The accuracy of the improved method is verified by the mechanical test method.Sexuality,and explored the reliability of using this improved method to measure tendon tissue in pigs.Based on the programmable Verasonics(TM)Vantage256 ultrasound open platform,a linear array probe L7-4 probe was controlled by the precision defined sequence to perform three acoustic radiation force excitation-plane wave acquisition processes,and different delay times were set for the trigger signal of the plane wave acquisition process to obtain different phases.The displacement data was reconstructed with data from three acquisition.With a sampling rate that is three times faster than original one,the vibration displacement curve can be more accurately described,and the shear wave velocity can be accurately calculated.The shear wave group velocity of the phantom was estimated by the peak time method(TTP)and the Radon transform,and the Young's modulus was estimated.At the same time,Fourier transform were used to calculate the phase velocity at different frequencies.Finally,the corresponding elasticity was obtained based on the nonlinear fitting of Voigt model.In order to evaluate the feasibility and accuracy of TDPM methods,this study first compares the measurements of shear wave velocity in self-made gelatin phantom made by TDPM and SPM and and then compares the estimated Young's modulus with uniaxially tensile MT.The results show that results of TDPM is closer to that of MT,moreover,TDPM measurement are stabler with small random error and high precision,which is the advantage of this method.Taking the PVA phantom of different freeze-thaw cycles as the research object,the performances of TDPM,SPM and TSPM were further compared.The results show that the overall performance of TSPM is better than that of SPM.Owing to high time resolution in TDPM,the measurement is more stable with small random error,especially for the phantom of higher stiffness.At the same time,the measurement results of uniform phantoms at different depths also indicate that the TDPM method is less affected by depth and the error caused by depth change is relative small.Finally,we investigated the reliability of shear wave velocity(SWS)measured by TDPM and SPM with the tendon tissue in pigs.The results show that the mean SWS goodness of TDPM and SPM are 0.94 and 0.87 respectively.And the estimated elastic modulus of TDPM is very close to the mechanical test results.In this paper,the feasibility and accuracy of the proposed ultrasonic measurement method for triple different phase excitation modes(TDPM)was evaluated and validated.The method shows good reproducibility and small random error in the shear wave velocity measurement of the phantom and tissue.The shear wave velocity measurement of harder tissue is more reliable,which is an important advantage and it is promising to become a more effective method for estimating shear wave of high stiffness.