| Cardiovascular diseases are the biggest killer of human life,and the number of people dying of cardiovascular diseases have increased gradually,which has become a serious public health problem in China.Arterial stiffness has been recognized as an important independent predictor of various cardiovascular diseases.Therefore,accurate detection of arterial stiffness can help cardiovascular patients to detect and treat early,and reduce morbidity and mortality.Shear wave elastography(SWE)is a quantitative noninvasive technology to detect the mechanical properties of vascular wall,and it can pick up pressure-induced stiffening of arteries and be sensitive to arterial anisotropy.Previous studies demonstrated the feasibility of SWE in arteries and vascular phantoms but all relied on the longitudinal view.However,the artery is mechanically anisotropic;therefore,assessing arterial shear modilus in transverse directions is indispensable.The purpose of this study is to estimate vascular elasticity in both longitudinal and transverse directions by SWE,and to verify the accuracy of the two methods by tensile tests.A research platform was built up on the basis of Verasonics Vantage256 ultrasonic programmable system,a liner array transducer is controlled to produces acoustic radiation force on the vessel wall and the local vibration of the tissue is produced on the vessel wall.Then the high frame rate plane wave is transmitted to trace Lamb wave propagation.Lamb wave propagation data of longitudinal and transverse directions in vascular be obtained by changing the direction of the transducer.The Lamb wave group velocity,phase velocity dispersion curve,shear modulus of elasticity estimated by group velocity and phase velocity are calculated respectively.We made three kinds of vascular phantoms using PVA in combination with freeze-thaw(F/T)cycle and we used water column to produce three diferent pressure levels(60mm Hg,80 mm Hg and 100 mm Hg)to vascular phantoms respectively for reproducing the real vascular pressure environment.We preformed the longitudinal and transverse measurements of the vascular by SWE and cyclic tensile tests under pressure levels.First,we compare the shear elastic in longitudinal and transverse direction and shear modulus elastic calculated by tensile tests.Then,we compare the shear modulus of elastic of two direction of vascular and the shear modulus of elastic calculated by tensile tests in different intravascular pressure.The results found that the shear elastic modulus calculated by the group velocity and shear modulus tested by mechanical testing has significant difference(P<0.05),shear modulus of elastic fitted by the phase velocity of longitudinal closest to test results of tensile tests.There is no significant difference between the shear modulus of elastic calculated by the phase velocity of the longitudinal rear wall and the tensile test.The shear modulus of elastic of longitudial rear wall of 3F/T,4F/T and 5F/T were 57.12±6.5k Pa?114.4±7.3k Pa?127.21±10.3k Pa and the shear modulus of elastic of tensile tests were 57.12±6.5k Pa?114.4±7.3k Pa?127.21±10.3k Pa respectively in pressure level of 60 mm Hg.Except for 3F/T vessel phantom,there was no significant difference between the shear modulus of elastic of ultrasonic measurement and the mechanical tests.The shear elasticity modulus in the transverse direction estimated by lamb wave phase velocity is related to the geometric shape of the vessel.The shear modulus of elastic estimated by phase velocity in inner wall were 106.84±5,130.4±18 and 154.73±20.There was no significant difference between the shear modulus of elastic of ultrasonic measurement and the mechanical tests except for 3F/T vessel phantoms.This research investigated the effect of some factors,including longitudinal and transverse wave propagation,group velocity and phase velocity,blood pressure,as well as propagation path,with assistance of PVA vessel phantoms.The results will be helpful to clinical application of ultrasound elastography for evaluating the arterial stiffness. |
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