The Study On The Signal Analysis And Pulsation Detection For Common Carotid Arteries With Three Layers Using Ultrasound Technique

The latest pathophysiological studies indicate that the initial symptom of the atherosclerosis associate with the tissue structure and the related parameters of dynamic features,such as the thickness change as well as axial and radial motion mode during a cardiac cycle,for the common carotid artery(CCA)with the intima,media and adventitia.Nevertheless,a lot of researches were only interested in the detection for the thickness of intima-media or the variation in thickness during a cardiac cycle,or because the different thickness changes for the three layers of the CCA,especially that of the intima-media,are less than a millimeter under the influence of the pulsatile blood pressure.Moreover,the differences in the tissue structure of each layer result in different ultrasonic echo distributions,and then speckle patterns on B-mode images.These is complex motion mode for three layers of the CCA during a cardiac cycle under the pulsatile blood pressure,the flow of blood and the different elasticity moduli for three layers.However,a great deal of researches only focus on the axial or radial displacement of vascular wall in a cardiac cycle.In view of the above-mentioned challenges about detection of the pulsating CCA,a new detection method for the pulsating CCA with three layers using ultrasound technique is proposed by study and analysis for the characteristic of ultrasonic echo signal for three layers of CCA from the healthy volunteers.An pulsating ultrasound simulation model for the CCA with three layers based on a three-dimensional scatterer phantom with the Gamma distribution is presented to accurate detect the motion mode of three layers for CCA during a cardiac cycle.Then,the simulated data could be useful for verification the accuracy and validity of the pulsating detection in this paper.The modeling process of this thesis is as follows: Firstly,based on a geometrical model according to the clinical size and structure of CCAs,a three-dimensional static scatterer phantom is constructed.The values of characteristic parameters conformed to the clinical feature,the simulating scatterer distribution,density and intensity of each layer are gain.Thereafter,the dynamic scatterer model is made based on the mechanics parameters and axial shift of during a cardiac cycle,and used to generate corresponding pulsating radio-frequency signal,envelope signal and B-mode image of the CCA wall using the Field II platform.The results indicate that the simulation results presenting the static geometrical-sizes and dynamical variations accord with the preset values,as well as the echo distributions conform to clinical versions.Therefore,the presented simulation model gives a method of performance evaluation for the detection of the ultrasound-based tissue structures and dynamic parameters for three layers of the CCA.For real-time,fast and accurate identification and measurement of the variation in thickness as well as the radial displacement,the threshold segmentation method for three layers of the isolated CCA of pig is proposed.The experimentation process is as follows: The healthy isolated CCA of pig is detected by ultrasonography based on different center frequencies,and gained the corresponding ultrasonic signals.Subsequently,this CCA is separated from the surrounding tissue by blunt dissection,as well as detected by ultrasonography based on different center frequencies and gained the ultrasonic data.Then,the healthy isolated CCA of pig is sliced and obtained the clinical thickness for each layer of CCA using microscope.The threshold values for segmentation of three layers are determined through comparing the thickness from the envelope signals and measurement of microscope.In view of the characteristic of saltation in the rising and falling edges of envelope signals,the position and thickness of three layers are extracted from two groups of envelope signals above.Finally,the results from the different methods are compared.The structure of CCA for pig is observed in normal blood pressure.The variation in thickness of intima-media as well as the radial displacements of intima-media and adventitia are extracted from the pulsating ultrasound simulation model for the CCA with three layers above and the continuously measuring clinical-data for the healthy volunteers based on the above-mentioned threshold segmentation method.The results show that the threshold values,based on the characteristic of the saltation in the rising and falling edges of envelope signals,could accurately detect the variation in thickness of intima-media as well as the radial displacements of intima-media and adventitia during a cardiac cycle for the pulsating ultrasound simulation model.These is also a good performance detection for the variation in thickness of intima-media as well as the radial displacements of intima-media and adventitia from the clinical data.Finally,the evaluation for axial motion mode of three layers for the CCA based on the feedback of the radial displacement of intima-media is presented in this paper in order to estimate the axial movement of intima-media.The window,which is selected to calculate cross-correlation in the speckle tracking algorithm,is adjusted by the detected axial-displacement curve of intima-media to protect the testing result from the radial movement of the vessel wall before the speckle tracking.Subsequently,the cross-correlations at all different times are computed for envelope signals in the selected window to acquire the axial displacement of intima-media for the simulated pulsatile-model during a cardiac cycle.The clinical axial-displacement of intima-media is measured using the above-mentioned evaluation method.The experimental results show that the axial movement of intima-media for the simulated results is in agreement with the theoretical one.The axial placement of intima-media from clinical data has obvious stages and periodicity,therefore this evaluation method has a good performance detection for axial placement of intima-media from the clinical data.In conclusion,the threshold segmentation method for three layers of CCA,based on the characteristic of saltation in the rising and falling edges of envelope signals,could improve the accuracy of estimation for the variation in thickness as well as the radial displacement of CCA.Further,the evaluation for axial motion mode of three layers for the CCA based on the feedback of the radial displacement of intima-media has a good performance detection.In order to detect the motion mode of three layers for CCA during a cardiac cycle and use the simulated data to verify the accuracy and validity of the pulsating detection in this thesis,an pulsating ultrasound simulation model for the CCA with three layers is presented.It could reflect not only different characteristics of echo distributions conforming to clinical ones,but also varying thicknesses,axial and radial displacements during a cardiac cycle.The research results can improve the reliability and validity of ultrasonic detection for the variation in thickness,the axial and radial displacements of three layers for the CCA during a cardiac cycle,and offer more advanced experimental measures about the early parameter detections for the related ultrasonic diseased-tissues of the cardiovascular disease.It has practical value to research early ultrasonic detection for cardiovascular disease.