The Study On The Ultrasonic Detection For The Wall Pulsation And Modulated Slow Blood Flow Of Carotid Arteries

In clinical practice and research,to assess the artery lesions,ultrasound is often used to measure the arterial wall displacement and the velocity of blood flow.However,during the actual measurement procedure of the pulsatile wall displacement,the unavoidable interferences,such as the probe jitter,the subject's breathing,heartbeat and other factors,will introduce errors in the results.Furthermore,the slowly pulsatile artery wall will reflect the high-intensity low-frequency ultrasonic echo signal,which will cause very serious interference to the low-amplitude high-frequency ultrasonic echo signal reflected by the blood cells,especially to the echo by near-wall slow blood flow.However,it precisely includes the sensitive parameters to early diagnosis of disease.Therefore,how to remove the external interference during the test procedure,suppress the interference of high-power wall echo signal are studied in this paper.Firstly,in order to improve the detection accuracy of the wall pulsation and suppress the external disturbance,a registration method,the position weighted principal axis and centroid method,using phase images are introduced.This method is based on the fact that the areas,which is far away from the artery,in these sequential B-mode images are almost stable,and are hardly influenced by the pulsatile of the arterial wall.Further,we propose a new registration method based on gray level-gradient co-occurrence matrix(GLCM).Taking advantage of the texture information,this method achieves better registration results.The results show that,compared with that of using B-image directly,the tracking accuracy is improved by 45%for position weighted principal axis and centroid method,and is improved by 47.8%for gray level-gradient co-occurrence matrix method.Furthermore,the processing results of the clinical B-mode images illustrate that with these two new methods,more precise estimation of vessel wall motion can be obtained.In order to more effectively suppress the low frequency and high amplitude ultrasound signal reflected by the vessel wall,a clutter rejection method based on local mean decomposition(LMD)is proposed in this paper.The new method decomposes Doppler signals into a set of functions,each of which is the product of an envelope signal and a frequency modulated signal from which a time-varying instantaneous frequency and amplitude can be derived.Based on the instantaneous frequency and amplitude,a blood-wall index is introduced to separate the blood signal from wall signal in the same layer,and a layer index is introduced to determine which layer includes both blood and wall component.Thus,a more fine separation between blood and wall is realized.Aiming at the mode mixing problem of LMD,and the application of the LMD algorithm to the wall clutter suppression of the quadrature Doppler signal of blood flow in the carotid artery,a noise-assisted LMD algorithm and a multivariable LMD algorithm are introduced.Compared with the EMD method based on phase filtering,both methods introduced in this paper reduce the normalized root mean square errors of obtained blood signal by about 50%,40%and 40%when the wall flow power ratio is 20dB,40dB and 60dB,respectively.The experimental results and simulation results show that these two methods can effectively filter the wall clutter signal,and retain more low-speed blood flow signal.In order to verify the introduced methods,and provide realistic data sources for research,a fluid-structure interaction(FSI)ultrasonic simulation model of the CA,which combine numerical modeling with ultrasonic simulation,is proposed in this paper.This simulation model takes into account the fluid-solid coupling between the vessels and flow,can simulate ultrasonic signal of the oscillating wall and blood flow modulated by the wall.Moreover,the stenosis narrow degree,the oscillating amplitude and frequency of the wall can be set in this simulation model.Furthermore,a simulation method combining clinical ultrasound image and simulated ultrasound signal is proposed in this work.The results show that the simulation model can mimic ultrasonic signals and ultrasound images with high similarity to clinical data,and provide realistic simulation sources for the detection of the motion of wall and the detection of the slow blood flow ultrasonic signal modulated by the wall.