Carotid Artery Elastography Based On Ultrasound Pulse Wave Imaging

Atherosclerosis may progress silently without symptoms and contribute to acute cardiovascular events such as heart attack,stroke,and cerebral thrombosis,which are consistently among the leading causes of death worldwide.The arterial pulse wave,regarded as one of an important index reflecting arterial elasticity,originates from the heart and propagates throughout the arterial tree giving rise to the natural pulsation of the arteries.The pulse wave velocity(PWV)is regarded as the golden standard to evaluate arterial elasticity in clinic.Traditionally,PWV is measured as a mean value for a long path of vessels.However,it differs at different locations.Therefore,we need to measure the local PWV of regional vascular to reflect the mechanical properties of vascular more accurately.The main purpose of this thesis is to develop a new imaging method,to measure and image the regional PWV quantitatively so that to evaluate the mechanical properties of local vascular wall together with the plaques.The existing PWV measurement techniques such as vascular-echo-tracking method are poor in reproducibility and accuracy.Another typical PWV measurement technology is named Ultra Fast PWV,however,its applications are limited.Pulse wave imaging(PWI)is a new technique to measure pulse wave velocity and can capture any blood vessel position of the pulse wave propagation,and to provide vascular elasticity information.PWI has not been applied to clinic yet.This thesis explores the clinical feasibility of quantitative assessment of vascular stiffness using PWI.In this study we propose a new imaging method(piece-wise pulse wave imaging,piecewise PWI)to measure the hardness of the wall and plaque of the local vessels.Our work includes the following parts: 1)we develop a finite element model using COMSOL to simulate the fluid-solid coupling of blood-wall to capture the pulse wave on the vessel wall.The relationship between PWV and the Young’s modulus of artery wall is studied.It is confirmed that the PWV is highly correlated with vascular stiffness;2)we study various algorithms of speckle tracking in piece-wise PWI,and select one from them for tracking the displacement of blood vessel wall according to the balance among SNR,CNR and computation cost.We also investigate how much the vascular hardness influenced by different ultrasonic data processing methods,and evaluate the result with phantom study.The mechanical properties of blood vessel phantom are simultaneously measured by a standard biomechanical testing instrument,for the validation of ultrasound results;3)Aiming to improve image quality of piece-wise PWI in contrast to the current techniques which reduce the linear density to increase the frame rate.we propose a plane wave imaging technique is for piece-wise PWI.The feasibility of the method was confirmed by the experiments on vessel phantom;4)Cooperating with the ultrasound department of Shenzhen second people’s hospital,we collect the clinical trial data of normal and subjects with atherosclerosis,to measure PWV and mechanical properties of their carotid arteries.We find that our proposed PWI method not only can distinct the wall and the plaque,but also can localize the junction of the wall position and plaque,with high spatial resolution and contrast of the distribution of the mechanical properties along the vessel wall.