Two-Way Fluid-Structure Interaction Simulation Of Abdominal Aortic Aneurysm Based On CTScan Data

Abdominal aortic aneurysm(AAA)is a common and life-threatening arterial disease.The prevalence rate among people over 65 years old is 8.9%.With the increasing aging of the population,the incidence of AAA is on the rise.If not treated in time,AAA will gradually expand to rupture.In case of tumor rupture and massive bleeding,the mortality rate is as high as 90%even after emergency operation.However,most of AAA patients are asymptomatic,and it is difficult to detect and treat early.At present,the physiological and pathological mechanism of AAA is not completely clear,and it is impossible to directly measure the tissue stress and intensity of the lesions in clinic.The current treatment about AAA is mainly surgical intervention,but because of no symptoms before rupture,it is difficult for surgeons to predict the risk of tumor rupture and determine the best time of surgical intervention.With the development of computational fluid mechanics,many scholars have used computer simulation analysis to study AAA,but most of them use idealized models,which cannot accurately simulate the biomechanical environment of AAA in human bodys.Therefore,it is of great significance to understand the generation,growth and rupture mechanism of AAA by using real AAA model to simulate the hemodynamics of AAA in human physiological environment so as to pursue the stress distribution and deformation process of AAA.The AAA simulation model established in this paper is composed of blood vessel wall and blood.The geometric model is completed by the CT scan images of a specific AAA which have been ruptured.The model highly restores the complex structural characteristics of the real AAA.The mathematical model is a constitutive model defined by the material properties of blood vessel wall and blood.Based on the constitutive model of each part and the theory of fluid structure coupling analysis,a separate algorithm is used to complete the numerical solution of the two-way fluid-structure coupling.The fluid domain is based on the finite volume method to solve the pressure velocity coupling equation of the three-dimensional transient standard turbulence model under the arbitrary Lagrange Euler frame,while the solid domain is solved by the dual nonlinear finite element method considering the inherent material nonlinearity of the vessel wall and the geometric nonlinearity caused by the tumor lesions.On the coupling boundary,it is necessary to ensure the displacement compatibility,stress balance and no slip of velocity between fluid domain and solid domain.Based on the theoretical research of AAA fluid structure coupling analysis,the two-way fluid structure coupling simulation analysis is completed.In the fluid domain,the flow velocity and turbulence characteristics of blood and their influence on the wall shear stress are mainly investigated.In the solid domain,the stress and deformation process of the vessel wall are mainly analyzed.In the flow field analysis,it is found that the flow at the bend and bifurcation of the blood vessel is the most complex,reaching the peak velocity(0.5404m/s)and the peak vortex flow(23.9254s-1)in about 0.3s,but the blood in the lower half of the tumor shows a low-speed and unstable flow state,and the tumor wall is exposed to low shear stress for a long time,which will lead to a series of adverse reactions such as inflammation in the lower half of the tumor,and finally increase risk of tumor rupture.In the structural analysis,it is found that although there is a small range of stress concentration in the areas with complex blood flow,such as the inside of curved vessels,near the entrance of the tumor and bifurcated vessels,the large strain concentration area and the high stress concentration area are located in the posterior wall of the tumor,and the posterior wall is subjected to the peak stress(591.4kpa)at about 0.34s,which accounts for 91%of the ultimate strength of the tumor wall.To sum up,we can see that the risk of posterior wall rupture is extremely high,and surgical intervention is urgently needed.This conclusion is also consistent with clinical practice.In this paper,we restored an unruptured AAA model based on the CT scan data of a specific patient who suffered from AAA ruptured.Then established a complete 3D geometric model and mathematical model of AAA.Through the two-way fluid structure coupling simulation analysis,the specific location of the rupture was accurately predicted,and the main mechanical factors and secondary factors affecting the rupture of the tumor were revealed,which further confirms the feasibility of the simulation analysis to predict AAA rupture,provides a reliable basis for the application of simulation software in clinical medicine as well.