基于CT断层扫描的主动脉夹层的流体动力学分析
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摘要
主动脉夹层,也称为主动脉夹层动脉瘤,是一种严重危害病人健康的急性主动脉疾病。临床上发现主动脉夹层的发病率呈逐年增加的趋势。如果不加以治疗,随着血管腔内压力的不断推动,夹层被撕裂的程度越来越大,血管管壁变薄,最终可能导致夹层的破裂,病死率高达80%～90%。临床上采取的治疗方法主要是内科保守治疗和外科根治性手术治疗。目前对于主动脉夹层的发病机理及内膜破口的撕裂位置并没有具体阐明,手术治疗还不是非常成熟。因此,从流体动力学角度研究主动脉夹层动脉瘤,可为临床治疗主动脉夹层提供重要的指导意义。
本文首先对目前研究较多的理想化的主动脉瘤模型进行了数值计算,从而验证本文所采用的数值计算方法的有效性和可靠性。对于理想化的主动脉瘤模型,利用流体计算软件FLUENT计算,从而得出主动脉瘤内部的流场变化及壁面受到的血液的冲击切应力和静态压力;利用流体动力学软件ANSYS-CFX进行流固耦合计算,通过与正常的血管进行比较,分析病变血管承受的血流对于壁面的影响,得出了病变血管易发生破裂的位置,从而验证了数值计算方法的有效性和可靠性。
论文的主要工作是根据CT断层扫描得到的527张主动脉夹层的切片图,通过医学处理软件3D-DOCTOR读取DICOM数据,通过实体逆向重构软件GEOMAGIC重构出真实的主动脉夹层、真腔及假腔。利用流体计算软件FLUENT进行数值计算,分析主动脉夹层、真腔及假腔内部的流场特征,得出主动脉夹层壁面及内膜片受到的血液的冲击切应力及静态压力,分析管壁的危险位置,为临床上手术治疗主动脉夹层提供必要的指导;利用流体动力学软件ANSYS-CFX进行流固耦合计算,分析主动脉夹层的真腔及假腔的变形,得出管壁上的变形分布。本文采用的模型真实可靠,采用的边界条件是临床上通过核磁扫描得出的真实的速度、压力条件。数值计算结果表明:主动脉夹层破口附近壁面受到的剪切力会急剧的增大,假腔顺向扩展的趋势强于逆向扩展的趋势。计算中采用弹性壁面时计算得到的壁面切应力比刚性壁面时小,因此采用刚性壁面的计算结果是偏于安全的。
Aortic dissection, which is also called aortic dissection aneurism, is an acute aortic disease which can bring serious harm to the health of patients. The incident of aortic dissection was found in an increasing trend year by year clinically. If not treated, with the persistent efforts of the pressure in vessel cavity, the extent of the dissection is torn growing, and the vascular wall is becoming thinner. And all of these could eventually lead to rupture of aortic dissection. And the case-fatality rate is as high as 80～90 percent. Methods adopted clinically are conservative treatment and surgical treatment. At present, the pathogenesis of aortic dissection and the aortic dissection rupture location have not been specified clearly, and surgical treatment of aortic dissection is not yet mature. As a result of these reasons, it is meaningful for fluid dynamic analysis on aortic dissection which can provide important guiding significance clinically.
Firstly, the current study of more idealized model of aortic aneurysm has been calculated which is used to validate the proficiency and reliability of the numerical method. For the idealized aortic aneurysm, the characteristics of the flow field of the aortic aneurysm and distribution of the shear stress and static pressure of the wall can be gotten by CFD software FLUENT. The interaction between fluid and solid can be calculated by fluid dynamic software ANSYS-CFX. Compared with the normal blood vessels, it is helpful for the clinical treatment of the aortic aneurysm. And the proficiency and the reliability of the numerical method can be validated, which can provide a reliable method for the next calculation of aortic dissection.
The major work is based on the 527 slices of aortic dissection obtained by computerized tomography scan. The absolute aortic dissection, true lumen and false lumen can be reconstructed by the medical processing software 3D-DOCTOR and the physical reconstructing software GEOMAGIC. The characteristics of the flow field of the aortic dissection, true lumen and false lumen can be calculated and analyzed by CFD software FLUENT. Thus, distribution of the shear stress and the static pressure of the wall and the initial flap of aortic dissection can be gotten. And the risk position of the wall can also be analyzed, which can provide clinical guidance on the surgical treatment of aortic dissection. In addition, the interaction between the fluid and solid can be gotten by ANSYS-CFX, and the deformation of the true lumen and the false lumen can be analyzed, thus the deformation distribution of the wall can be gotten. The model is real, and the velocity and pressure boundary conditions are obtained by magnetic resonance imaging(MRI). The results show that wall shear stress becomes larger rapidly near the break point. The forward extension of false lumen increases faster than reverse extension. The deformation of the flexible wall is larger than that of the rigid wall, but the shear stress on the flexible wall is much smaller.
本文首先对目前研究较多的理想化的主动脉瘤模型进行了数值计算,从而验证本文所采用的数值计算方法的有效性和可靠性。对于理想化的主动脉瘤模型,利用流体计算软件FLUENT计算,从而得出主动脉瘤内部的流场变化及壁面受到的血液的冲击切应力和静态压力;利用流体动力学软件ANSYS-CFX进行流固耦合计算,通过与正常的血管进行比较,分析病变血管承受的血流对于壁面的影响,得出了病变血管易发生破裂的位置,从而验证了数值计算方法的有效性和可靠性。
论文的主要工作是根据CT断层扫描得到的527张主动脉夹层的切片图,通过医学处理软件3D-DOCTOR读取DICOM数据,通过实体逆向重构软件GEOMAGIC重构出真实的主动脉夹层、真腔及假腔。利用流体计算软件FLUENT进行数值计算,分析主动脉夹层、真腔及假腔内部的流场特征,得出主动脉夹层壁面及内膜片受到的血液的冲击切应力及静态压力,分析管壁的危险位置,为临床上手术治疗主动脉夹层提供必要的指导;利用流体动力学软件ANSYS-CFX进行流固耦合计算,分析主动脉夹层的真腔及假腔的变形,得出管壁上的变形分布。本文采用的模型真实可靠,采用的边界条件是临床上通过核磁扫描得出的真实的速度、压力条件。数值计算结果表明:主动脉夹层破口附近壁面受到的剪切力会急剧的增大,假腔顺向扩展的趋势强于逆向扩展的趋势。计算中采用弹性壁面时计算得到的壁面切应力比刚性壁面时小,因此采用刚性壁面的计算结果是偏于安全的。
Aortic dissection, which is also called aortic dissection aneurism, is an acute aortic disease which can bring serious harm to the health of patients. The incident of aortic dissection was found in an increasing trend year by year clinically. If not treated, with the persistent efforts of the pressure in vessel cavity, the extent of the dissection is torn growing, and the vascular wall is becoming thinner. And all of these could eventually lead to rupture of aortic dissection. And the case-fatality rate is as high as 80～90 percent. Methods adopted clinically are conservative treatment and surgical treatment. At present, the pathogenesis of aortic dissection and the aortic dissection rupture location have not been specified clearly, and surgical treatment of aortic dissection is not yet mature. As a result of these reasons, it is meaningful for fluid dynamic analysis on aortic dissection which can provide important guiding significance clinically.
Firstly, the current study of more idealized model of aortic aneurysm has been calculated which is used to validate the proficiency and reliability of the numerical method. For the idealized aortic aneurysm, the characteristics of the flow field of the aortic aneurysm and distribution of the shear stress and static pressure of the wall can be gotten by CFD software FLUENT. The interaction between fluid and solid can be calculated by fluid dynamic software ANSYS-CFX. Compared with the normal blood vessels, it is helpful for the clinical treatment of the aortic aneurysm. And the proficiency and the reliability of the numerical method can be validated, which can provide a reliable method for the next calculation of aortic dissection.
The major work is based on the 527 slices of aortic dissection obtained by computerized tomography scan. The absolute aortic dissection, true lumen and false lumen can be reconstructed by the medical processing software 3D-DOCTOR and the physical reconstructing software GEOMAGIC. The characteristics of the flow field of the aortic dissection, true lumen and false lumen can be calculated and analyzed by CFD software FLUENT. Thus, distribution of the shear stress and the static pressure of the wall and the initial flap of aortic dissection can be gotten. And the risk position of the wall can also be analyzed, which can provide clinical guidance on the surgical treatment of aortic dissection. In addition, the interaction between the fluid and solid can be gotten by ANSYS-CFX, and the deformation of the true lumen and the false lumen can be analyzed, thus the deformation distribution of the wall can be gotten. The model is real, and the velocity and pressure boundary conditions are obtained by magnetic resonance imaging(MRI). The results show that wall shear stress becomes larger rapidly near the break point. The forward extension of false lumen increases faster than reverse extension. The deformation of the flexible wall is larger than that of the rigid wall, but the shear stress on the flexible wall is much smaller.
引文
[1]张兆琪,等.心血管疾病磁共振成像.北京:人民卫生出版社.2007:224-226.
[2] Budwig R, Elger D, Hooper H, et al. Steady flow in abdominal aortic aneurysm models. ASME Journal of Biomechanical Engineering. 1993, 115:418-423.
[3] Bluestein D, Niu L, Schoephoerster RT, et al. Steady flow in an aneurysm model: correlation between fluid dynamics and blood platelet deposition. ASME Journal of Biomechanical Engineering. 1996,118:280-286.
[4] Nerem RM, Alexander RW, et al. The study of the fluence of flow on vascular endothelial biology. Computer Graphics. 1987,21(4):163-169.
[5] Fann JI, Sarris GE, Mitchell RS, et al. Treatment of patients with aortic dissection presenting with peripheral vascular complications. Ann Surg. 1990,212:705-713.
[6] Cambria RP, Brewster DC, Gertler J, et al. Vascular complications associated with spontaneous aortic dissection. J Vasc Surg. 1998,27:199-209.
[7]高元桂,蔡幼铨,蔡祖龙,等.磁共振成像诊断学.北京:人民军医出版社.1993:416~420.
[8] Carsten J, Beller MD, et al. Role of Aortic ROOt Motion in the Pathogenesis of Aortic Dissection. Circulation. 2004,109:763-769.
[9] Raghavan ML, Vorp DA, Federle MP, et al. Wall stress distribution on three dimensionally reconstructed models of human abdominal aortic aneurysm. J Vasc Surg 2000,31:760-769.
[10] Crawford ES, Coselli JS, Svensson LG, et al. Diffuse aneurismal disease and multiple aneurysm. Ann surg. 1990, 211:521.
[11] Debakey ME, McCollum CH, Crawford ES, et al. Dissection and dissecting aneurysms of the aorta: twenty-year follow-up of five hundred twenty-seven patients treated surgically. Surgery. 1982, 92: 1118-1132.
[12] Carrel T, Nguyen T, Gysi J, et al. Acute type B aortic dissection: prognosis after initial conservative treatment and predictive factors for a complicated course. Schweiz Med Wochenschr. 1997,127(36):1467~1473.
[13] Bickerstaff LK, Pairolero PC, Hollier LH, et al. Thoracic aortic aneurysms: a population-based study. Surgery. 1982, 92(6):1103-1108.
[14] Chen K, Varon J, Wenker OC, et al. Acute thoracic aortic dissection: the basis. J Emerg Med. 1997, 15(6):859-867.
[15] Wheat MW Jr, Palmer RJ, Bartley TB, et al. Treatment of dissecting aneurysms of aorta without surgery. J Thorac Cardiovasc Surg. 1965,50:364-373.
[16] Prokop EK, Palmer RF, Wheat MW Jr. Hydrodynamic forces in dissecting aneurysms. In-vitro studies in a Tygon model and in dog aortas. Circulation Research. 1970, 27(1):121-127.
[17] Carney WI Jr, Rheinlander HF, Cleveland RJ. Control of acute aortic dissection. Surgery. 1975, 78(1):114-120.
[18] Moran JF, Derkac WM, Conkle DM. Pharmacologic control of acute aortic dissection in hypertensive dogs. Surg Forum. 1978,29:231-234.
[19] Milner JS, Moore JA, Rutt BK, et al. Hemodynamics of human carotid artery bifurcations: computational studies with models reconstructed from magnetic resonance imaging of normal subjects. J Vasc Surg. 1998,28:143-156.
[20] Yu SCM, Chan WK, Ng BTH, et al. A numerical investigation on the steady and pulsatile flow characteristics in axia-symmetric abdominal aortic aneurysm models with some experimental evaluation. Journal of Medical Engineering &Technology. 1999, 23(6):228-239.
[21] Martino D, Guadagni E S, Fumero G, et al. Fluid–structure interaction within realistic three-dimensional models of the aneurysmatic aorta as a guidance to assess the risk of rupture of the aneurysm. Medical Engineering & Physics. 2001, 23: 647-655.
[22] Valencia A, Villanueva M. Unsteady flow and mass transfer in models of stenotic arteries considering fluid-structure interaction. International Communications in Heat and Mass Transfer. 2006, 33: 966-975.
[23] Li M X, Beech B J, John L, et al. Numerical analysis of pulsatile blood flow and vessel wall mechanics in different degrees of stenoses. Journal of Biomechanics. 2007, 40: 3715-3724.
[24] Di Martino ES and Guadagni G. Fluid-structure interaction within realistic three-dimension models of the aneurysmatic aorta as a guidance to assess the risk of rupture of the aneurysm. Medical Engineering&Physics. 2001,23:647-655.
[25] Nichols WW and O’Rourke MF. McDonald’s Blood Flow in Arteries. London: Lea and Febiger. 1990.
[26] Pektold K, Resch M, Florian H. Pulsatile non-Newtonian flow characteristics in a three-dimension human carotid artery bifurcation model. ASME Journal of Biomechanical Engineering. 1991, 113:464-475.
[27] Feng Y, Shigeo W, K Tsubota T Y. A Model-based Numerical Analysis in the Early Development of Intracranial Aneurysms: Proceedings of the 2005 IEEE Engineering in Medicine and Biology 27th Annual Conference. Shanghai, China. 2005, 1(4).
[28] Chatziprodromou I, Tricoli A, Poulikakos D, et al. Haemodynamics and wall remodelling of a growing cerebral anerysm: a computational model. Journal of Biomechnics. 2007, 40: 412-426.
[29] Fry DL. Certain Histological and Chemical Responses of the Vascular Interface to Acutely Induced Mechanical Stress in the Aorta of the Dog. Circulation Research. 1969,14:93-108.
[30] http://ablesw.com/3D-DOCTOR/.
[31] Qiu TX, Teo EC. Finite element modeling of human thoracic spine. Journal of Musculoskeletal Research. 2004,8(4):133-144.
[32]胡勇,谢晖,杨述华.三维有限元分析在生物力学中的应用研究.医用生物力学.2006,21(3):246-250.
[2] Budwig R, Elger D, Hooper H, et al. Steady flow in abdominal aortic aneurysm models. ASME Journal of Biomechanical Engineering. 1993, 115:418-423.
[3] Bluestein D, Niu L, Schoephoerster RT, et al. Steady flow in an aneurysm model: correlation between fluid dynamics and blood platelet deposition. ASME Journal of Biomechanical Engineering. 1996,118:280-286.
[4] Nerem RM, Alexander RW, et al. The study of the fluence of flow on vascular endothelial biology. Computer Graphics. 1987,21(4):163-169.
[5] Fann JI, Sarris GE, Mitchell RS, et al. Treatment of patients with aortic dissection presenting with peripheral vascular complications. Ann Surg. 1990,212:705-713.
[6] Cambria RP, Brewster DC, Gertler J, et al. Vascular complications associated with spontaneous aortic dissection. J Vasc Surg. 1998,27:199-209.
[7]高元桂,蔡幼铨,蔡祖龙,等.磁共振成像诊断学.北京:人民军医出版社.1993:416~420.
[8] Carsten J, Beller MD, et al. Role of Aortic ROOt Motion in the Pathogenesis of Aortic Dissection. Circulation. 2004,109:763-769.
[9] Raghavan ML, Vorp DA, Federle MP, et al. Wall stress distribution on three dimensionally reconstructed models of human abdominal aortic aneurysm. J Vasc Surg 2000,31:760-769.
[10] Crawford ES, Coselli JS, Svensson LG, et al. Diffuse aneurismal disease and multiple aneurysm. Ann surg. 1990, 211:521.
[11] Debakey ME, McCollum CH, Crawford ES, et al. Dissection and dissecting aneurysms of the aorta: twenty-year follow-up of five hundred twenty-seven patients treated surgically. Surgery. 1982, 92: 1118-1132.
[12] Carrel T, Nguyen T, Gysi J, et al. Acute type B aortic dissection: prognosis after initial conservative treatment and predictive factors for a complicated course. Schweiz Med Wochenschr. 1997,127(36):1467~1473.
[13] Bickerstaff LK, Pairolero PC, Hollier LH, et al. Thoracic aortic aneurysms: a population-based study. Surgery. 1982, 92(6):1103-1108.
[14] Chen K, Varon J, Wenker OC, et al. Acute thoracic aortic dissection: the basis. J Emerg Med. 1997, 15(6):859-867.
[15] Wheat MW Jr, Palmer RJ, Bartley TB, et al. Treatment of dissecting aneurysms of aorta without surgery. J Thorac Cardiovasc Surg. 1965,50:364-373.
[16] Prokop EK, Palmer RF, Wheat MW Jr. Hydrodynamic forces in dissecting aneurysms. In-vitro studies in a Tygon model and in dog aortas. Circulation Research. 1970, 27(1):121-127.
[17] Carney WI Jr, Rheinlander HF, Cleveland RJ. Control of acute aortic dissection. Surgery. 1975, 78(1):114-120.
[18] Moran JF, Derkac WM, Conkle DM. Pharmacologic control of acute aortic dissection in hypertensive dogs. Surg Forum. 1978,29:231-234.
[19] Milner JS, Moore JA, Rutt BK, et al. Hemodynamics of human carotid artery bifurcations: computational studies with models reconstructed from magnetic resonance imaging of normal subjects. J Vasc Surg. 1998,28:143-156.
[20] Yu SCM, Chan WK, Ng BTH, et al. A numerical investigation on the steady and pulsatile flow characteristics in axia-symmetric abdominal aortic aneurysm models with some experimental evaluation. Journal of Medical Engineering &Technology. 1999, 23(6):228-239.
[21] Martino D, Guadagni E S, Fumero G, et al. Fluid–structure interaction within realistic three-dimensional models of the aneurysmatic aorta as a guidance to assess the risk of rupture of the aneurysm. Medical Engineering & Physics. 2001, 23: 647-655.
[22] Valencia A, Villanueva M. Unsteady flow and mass transfer in models of stenotic arteries considering fluid-structure interaction. International Communications in Heat and Mass Transfer. 2006, 33: 966-975.
[23] Li M X, Beech B J, John L, et al. Numerical analysis of pulsatile blood flow and vessel wall mechanics in different degrees of stenoses. Journal of Biomechanics. 2007, 40: 3715-3724.
[24] Di Martino ES and Guadagni G. Fluid-structure interaction within realistic three-dimension models of the aneurysmatic aorta as a guidance to assess the risk of rupture of the aneurysm. Medical Engineering&Physics. 2001,23:647-655.
[25] Nichols WW and O’Rourke MF. McDonald’s Blood Flow in Arteries. London: Lea and Febiger. 1990.
[26] Pektold K, Resch M, Florian H. Pulsatile non-Newtonian flow characteristics in a three-dimension human carotid artery bifurcation model. ASME Journal of Biomechanical Engineering. 1991, 113:464-475.
[27] Feng Y, Shigeo W, K Tsubota T Y. A Model-based Numerical Analysis in the Early Development of Intracranial Aneurysms: Proceedings of the 2005 IEEE Engineering in Medicine and Biology 27th Annual Conference. Shanghai, China. 2005, 1(4).
[28] Chatziprodromou I, Tricoli A, Poulikakos D, et al. Haemodynamics and wall remodelling of a growing cerebral anerysm: a computational model. Journal of Biomechnics. 2007, 40: 412-426.
[29] Fry DL. Certain Histological and Chemical Responses of the Vascular Interface to Acutely Induced Mechanical Stress in the Aorta of the Dog. Circulation Research. 1969,14:93-108.
[30] http://ablesw.com/3D-DOCTOR/.
[31] Qiu TX, Teo EC. Finite element modeling of human thoracic spine. Journal of Musculoskeletal Research. 2004,8(4):133-144.
[32]胡勇,谢晖,杨述华.三维有限元分析在生物力学中的应用研究.医用生物力学.2006,21(3):246-250.