| Thrombosis is blood vessels in the cardiovascular system interior surface formed by the surface of the spalling or repair in small, often cause arterial partial blockage, cause organ ischemia, hypoxia and failure.Atherosclerosis is the main factor of thrombosis.Specific process of atherosclerosis lead to thrombosis is: atherosclerotic plaque rupture caused by vascular endothelial cells on the surface of the wall is damaged, the lesions adhesion platelets, gathered luminal stenosis, and make the blood coagulation system activation and thrombosis.Research has shown that situation does not occur in all of the atherosclerotic plaque rupture.No thrombosis of atherosclerotic plaque is called stable plaques, the plaque has a tendency to rupture is called vulnerable plaques. Vulnerable plaques is constructed by a thin fibrous cap, a wide range of macrophage infiltration, big fat nuclear etc, it can be through the examination of plaque composition to identify vulnerable plaques.Inspection methods on vulnerable plaques including imaging examination method and noninvasive imaging examination method. Invasive imaging examination method including vasography, Intravascular Ultrasound (IVUS) and Optical Coherence Tomography (OCT). Angiography currently have a clinical evaluation of atherosclerotic plaque and vascular cavity stenosis degree of the "gold standard", its operation method is relatively mature, simple and intuitive judgment way. But this method can only provide indirect, incomplete blood vessels disease information. Complex plaques of imaging findings of patients, is likely to mean that the existence of vulnerable plaques, and its specificity is relatively high; But for screening patients with no significant stenosis and complex plaques, also can’t rule out the existence of vulnerable plaques, the detection of a plaque sensitivity is poorer, therefore, vasography is not the preferred method for detecting vulnerable plaques. IVUS has good blood vessel penetrability, images can provide the detailed structure of the blood vessel walls, distinguish membrane, membrane and outer membrane. The sensitivity of the detection of lipid core reach 80%-90%. But the IVUS image resolution is about 100 μ m, may not be able to find cover lipid core thin fibrous cap. Optical coherence tomography has high resolution, high detectable plaque fractures, lipids and fibrous cap structure, recent study found that estimates by OCT plaques in the number of macrophages and pathology of measuring value highly correlated. OCT resolution can be up to 10 μ m, the resolution is less than 65 u m thickness of fibrous cap and higher sensitivity and specificity of fiber calcification. But because of its difficult have a check and is widely used in in the vulnerable plaques early identification of dynamic change.Noninvasive Imaging examination method including radionuclide Magnetic Resonance Imaging (MRI) and Computed Tomography Imaging (CT). Radionuclide imaging including Positron Emission Tomography imaging (PET) and single photon Emission computed Tomography imaging (SPECT), these two kinds of technology research and application of combined with specific markers, significantly improve the sensitivity of the artery detected vulnerable plaques and specific degrees. Studies have shown that the extent of the neck arteries inflammation and I8F-FDG positron labeled DNA (glucose)-PET uptake rate.18F-FDG PET can identify the neck artery inflammatory vulnerable plaques. Magnetic resonance (MR) is a kind of no ray imaging tool, high resolution can be reliably identified (carotid and peripheral arterial) vulnerability characteristics of atherosclerotic plaques. Emerging endovascular qualitative quantitative magnetic resonance imaging (fMRI) can show blood vessels (especially deep veins) tube wall and the structure of the plaque.multiple row spiral CT has a spatial resolution, Schroeder use cases do control plaque according to CT value points in three categories:soft plaque (rich in lipid plaques) acuities were 60 HU,61-119 HU, fibrous plaques, calcified plaque or 120 HU. To identify the vulnerable plaques two important features:large lipid core and positive refactoring plaques, but because of the lipid plaque between patches and CT value to distinguish the inaccurate, unable to identify the vulnerable plaques fibrous cap. The limitations of all three of these noninvasive method is a low resolution of space and time. So the high space-time resolution imaging method for the identification of vulnerable plaques has higher application value.Imaging methods by examining the structure and composition of the patch information to judge the plaque vulnerability.However, plaque will happen not only associated with the composition of plaque rupture, and patches of hemodynamic parameters.These parameters are mainly Shear force (Wall Shear Stress, WSS), Blood flow velocity, fluid state (such as the laminar Flow vortex Flow and turbulence, etc.).Ultrasound Particle Image Velocimetry (PIV) by Ultrasonic noninvasive testing method and the combination of hemodynamic parameters to conduct the risk assessment of vulnerable plaques.The technology is the use of imaging micro bubble strong launch of ultrasonic, by high resolution ultrasound imaging system to the regional image sequence, then on the two consecutive frames image cross-correlation calculation, and then obtain the flow field velocity distribution.PIV velocity experiment platform building and human blood circulation system with the same cycle fluctuation characteristics of fluid circulation system.Pulsating flow produced by pulse pump, through the liquid storage pool, transmission pipeline through the blood vessels of copy, make its produce periodic contraction and relaxation, through to the jerk pump frequency, stroke output, systolic/diastolic time than the parameters, such as regulation, make produce simulation imitation of human body blood vessels elastic characteristics of the movement.Ultrasonic Particle Image Velocimetry (PIV) is the use of imaging micro bubble strong launch of Ultrasonic, by high resolution ultrasound imaging system to the regional image sequence, then on the two consecutive frames image cross-correlation calculation, calculate the displacement of the micro bubbles in the image can be obtained, then the information distribution of flow field is obtained. Ultrasonic particle image velocimetry system is mainly composed of high resolution ultrasound system, an image sequence storage, image processing algorithms. Computational Fluid Dynamics (CFD) is the import and export by setting up a series of fluid boundary conditions using the computer to carry on the numerical simulation to calculate the flow field velocity distribution. CFD method the accuracy of the results depends on the reasonable selection of fluid model and wall function condition. This experiment in order to compare the PIV and CFD in the same experimental conditions of the experimental results, the traditional PIV velocity experiment platform is improved. Traditional PIV velocity experiment platform building and human blood circulation system with the same cycle fluctuation characteristics of fluid circulation system. Pulsating flow produced by pulse pump, through the liquid storage pool, transmission pipeline through the blood vessels of copy, make its produce periodic contraction and relaxation, through to the jerk pump frequency, stroke output, systolic/diastolic time than the parameters, such as regulation, make produce simulation imitation of human body blood vessels elastic characteristics of the movement. This experiment make improvements to traditional experiment platform are as follows:after the imitation devices with a pressure sensor, and through the oscilloscope read pressure waveform; Second placed in imitation of devices for the flowmeter, used to record the fluid flow. Pressure waveforms and fluid flow is the CFD simulation of the initial boundary conditions.Method:the test set of three groups of different degree of stenosis of vascular simulation, its size, in turn, of the three groups of simulation using PIV measuring the hemodynamic parameters and CFD method.Then on the basis of the three blood vessels imitation model design and production of the corresponding body mould, according to the freezing-thawing method, using PVA hydrogel preparation this a series of simulation experiments with blood vessels. At the same time set up with human blood circulation system with the same cycle fluctuation characteristics of fluid circulation system, contrast-enhanced ultrasound microbubble as tracer added to the fluid, fluid circulation system includes:produced by pulse pump pulse flow, through the liquid storage pool, the transmission pipelines, flow meter, pressure sensor to blood vessel body, make produce periodic contraction, blood vessels of copy, through to the jerk pump frequency, stroke output, systolic/diastolic time than the parameters, such as regulation, make produce simulation imitation of human body blood vessels elastic characteristics of the movement. In extracorporeal circulation experiments, Harvard Apparatus pulsating blood pump and body connection using silicone tube, in imitation of entrance section need reserved length to meet the entrance length, ensure the stable state of fluid motion. This experiment reserved length of 0.58 meters.Experimental process:using Vevo2100 ultrasonic molecular imaging system real-time acquisition of different stenosis degree simulation the flow field of ultrasound images, can by adjusting the frame rate of ultrasound device, the density of lines, image width to obtain the best parameters, such as ultrasonic images, each simulation to collect 1000 frames, image results using Matlab2014 software processing for PIV experiment results. Record at the same time under the condition of different device parameters simulation entry point meter readings, as well as the oscilloscope is read imitation inlet side and outlet pressure waveform of one cycle, the inlet flow, the inlet pressure, outlet pressure waveform into a UDF code, as the boundary condition is loaded into the AN SYS CFD simulation analysis software. At the same time take plaque before, during and after the three radial position, in three places respectively to compare the PIV and CFD blood flow velocity, and use Origin85 software processing results.Experimental process:using Vevo 2100 ultrasonic molecular imaging system real-time acquisition of different stenosis degree simulation the flow field of ultrasound images, can by adjusting the Frame Rate of ultrasound device, the Density of lines, Image Width to obtain the best parameters, such as ultrasonic images, each body Image acquisition of three phases of the cardiac cycle, Image results using Matlab2014 software processing for PIV experiment results.CFD simulation of the specific process is:according to the blood vessels of copy of body shape, in turn, the corresponding simulation model is established, the meshing model, at the same time the PIV experiment simulation entry point meter readings, as well as through the oscilloscope read simulation inlet side and outlet pressure waveform of one cycle, as the CFD simulation of inlet side flow, the inlet pressure, outlet pressure waveform and write into the UDF code, as the boundary condition is loaded into the ANSYS analysis software to simulate.Finally take plaque before, during and after the three radial location, in a cardiac cycle speed, biggest respectively to compare the three location PIV and CFD results, compare the results with Origin85 software processing.The result:the result of CFD and PIV method can accurately capture the plaque location before and after the change of the flow field, flow field on in front of the plaques, the closer the plaques, the trend of the upward movement of fluid, the more obvious, and there is an obvious backflow in the plaque at the back of the phenomenon;Plaque stenosis degree is higher, the backflow phenomenon is more obvious.Through the simulation experiment results of three groups of different degree of stenosis as you can see,30% stenosis degree of simulation, the fluid velocity is most close to CFD and PIV income;70% stenosis degree of simulation, two methods of speed is the most obvious, measured by PIV experiment results significantly lower than the CFD results. |
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