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\n\n \n \n Xenos, M.; Labropoulos, N.; Rambhia, S.; Alemu, Y.; Einav, S.; Tassiopoulos, A.; Sakalihasan, N.; and Bluestein, D.\n\n\n \n \n \n \n \n Progression of abdominal aortic aneurysm towards rupture: Refining clinical risk assessment using a fully coupled fluid–structure interaction method.\n \n \n \n \n\n\n \n\n\n\n
Ann. Biomed. Eng, 43: 139-153. 2015.\n
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@article{z17,\r\n author = {Xenos, M. and Labropoulos, N. and Rambhia, S. and Alemu, Y. and Einav, S. and Tassiopoulos, A. and Sakalihasan, N. and Bluestein, D.},\r\n year = {2015},\r\n title = {Progression of abdominal aortic aneurysm towards rupture: Refining clinical risk assessment using a fully coupled fluid–structure interaction method},\r\n journal = {Ann. Biomed. Eng},\r\n volume = {43},\r\n issue = {1},\r\n pages = {139-153},\r\n url_Link = {https://doi.org/10.1007/s10439-014-1224-0},\r\n abstract = {Rupture of abdominal aortic aneurysm (AAA) is associated with high mortality rates. Risk of rupture is multi-factorial involving AAA geometric configuration, vessel tortuosity, and the presence of intraluminal pathology. Fluid structure interaction (FSI) simulations were conducted in patient based computed tomography scans reconstructed geometries in order to monitor aneurysmal disease progression from normal aortas to non-ruptured and contained ruptured AAA (rAAA), and the AAA risk of rupture was assessed. Three groups of 8 subjects each were studied: 8 normal and 16 pathological (8 non-ruptured and 8 rAAA). The AAA anatomical structures segmented included the blood lumen, intraluminal thrombus (ILT), vessel wall, and embedded calcifications. The vessel wall was described with anisotropic material model that was matched to experimental measurements of AAA tissue specimens. A statistical model for estimating the local wall strength distribution was employed to generate a map of a rupture potential index (RPI), representing the ratio between the local stress and local strength distribution. The FSI simulations followed a clear trend of increasing wall stresses from normal to pathological cases. The maximal stresses were observed in the areas where the ILT was not present, indicating a potential protective effect of the ILT. Statistically significant differences were observed between the peak systolic stress and the peak stress at the mean arterial pressure between the three groups. For the ruptured aneurysms, where the geometry of intact aneurysm was reconstructed, results of the FSI simulations clearly depicted maximum wall stress at the a priori known location of rupture. The RPI mapping indicated several distinct regions of high RPI coinciding with the actual location of rupture. The FSI methodology demonstrates that the aneurysmal disease can be described by numerical simulations, as indicated by a clear trend of increasing aortic wall stresses in the studied groups, (normal aortas, AAAs and rAAAs). Ultimately, the results demonstrate that FSI wall stress mapping and RPI can be used as a tool for predicting the potential rupture of an AAA by predicting the actual rupture location, complementing current clinical practice by offering a predictive diagnostic tool for deciding whether to intervene surgically or spare the patient from an unnecessary risky operation.},\r\n project = {aaapatient},\r\n type = {1. Peer-Reviewed Journal Papers}\r\n}\r\n\r\n\n
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\n Rupture of abdominal aortic aneurysm (AAA) is associated with high mortality rates. Risk of rupture is multi-factorial involving AAA geometric configuration, vessel tortuosity, and the presence of intraluminal pathology. Fluid structure interaction (FSI) simulations were conducted in patient based computed tomography scans reconstructed geometries in order to monitor aneurysmal disease progression from normal aortas to non-ruptured and contained ruptured AAA (rAAA), and the AAA risk of rupture was assessed. Three groups of 8 subjects each were studied: 8 normal and 16 pathological (8 non-ruptured and 8 rAAA). The AAA anatomical structures segmented included the blood lumen, intraluminal thrombus (ILT), vessel wall, and embedded calcifications. The vessel wall was described with anisotropic material model that was matched to experimental measurements of AAA tissue specimens. A statistical model for estimating the local wall strength distribution was employed to generate a map of a rupture potential index (RPI), representing the ratio between the local stress and local strength distribution. The FSI simulations followed a clear trend of increasing wall stresses from normal to pathological cases. The maximal stresses were observed in the areas where the ILT was not present, indicating a potential protective effect of the ILT. Statistically significant differences were observed between the peak systolic stress and the peak stress at the mean arterial pressure between the three groups. For the ruptured aneurysms, where the geometry of intact aneurysm was reconstructed, results of the FSI simulations clearly depicted maximum wall stress at the a priori known location of rupture. The RPI mapping indicated several distinct regions of high RPI coinciding with the actual location of rupture. The FSI methodology demonstrates that the aneurysmal disease can be described by numerical simulations, as indicated by a clear trend of increasing aortic wall stresses in the studied groups, (normal aortas, AAAs and rAAAs). Ultimately, the results demonstrate that FSI wall stress mapping and RPI can be used as a tool for predicting the potential rupture of an AAA by predicting the actual rupture location, complementing current clinical practice by offering a predictive diagnostic tool for deciding whether to intervene surgically or spare the patient from an unnecessary risky operation.\n
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\n\n \n \n Xenos, M.; Alemu, Y.; Zamfir, D.; Einav, S.; Ricotta, J. J.; Labropoulos, N.; Tassiopoulos, A.; and Bluestein, D.\n\n\n \n \n \n \n \n The effect of angulation in abdominal aortic aneurysms: fluid-structure interaction simulations of idealized geometries.\n \n \n \n \n\n\n \n\n\n\n
Med Biol Eng Comput, 48: 1175-1190. 2010.\n
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@article{z41,\r\n author = {Xenos, M. and Alemu, Y. and Zamfir, D. and Einav, S. and Ricotta, J. J. and Labropoulos, N. and Tassiopoulos, A. and Bluestein, D.},\r\n year = {2010},\r\n title = {The effect of angulation in abdominal aortic aneurysms: fluid-structure interaction simulations of idealized geometries},\r\n journal = {Med Biol Eng Comput},\r\n volume = {48},\r\n issue = {12},\r\n pages = {1175-1190},\r\n url_Paper={/labs/dbluestein/PDF/Xenos_2010_AAA_angulation.pdf},\r\n url_Link = {https://doi.org/10.1007/s11517-010-0714-y},\r\n abstract = {Abdominal aortic aneurysm (AAA) represents a degenerative disease process of the abdominal aorta that results in dilation and permanent remodeling of the arterial wall. A fluid structure interaction (FSI) parametric study was conducted to evaluate the progression of aneurysmal disease and its possible implications on risk of rupture. Two parametric studies were conducted using (i) the iliac bifurcation angle and (ii) the AAA neck angulation. Idealized streamlined AAA geometries were employed. The simulations were carried out using both isotropic and anisotropic wall material models. The parameters were based on CT scans measurements obtained from a population of patients. The results indicate that the peak wall stresses increased with increasing iliac and neck inlet angles. Wall shear stress (WSS) and fluid pressure were analyzed and correlated with the wall stresses for both sets of studies. An adaptation response of a temporary reduction of the peak wall stresses seem to correlate to a certain extent with increasing iliac angles. For the neck angulation studies it appears that a breakdown from symmetric vortices at the AAA inlet into a single larger vortex significantly increases the wall stress. Our parametric FSI study demonstrates the adaptation response during aneurysmal disease progression and its possible effects on the AAA risk of rupture. This dependence on geometric parameters of the AAA can be used as an additional diagnostic tool to help clinicians reach informed decisions in establishing whether a risky surgical intervention is warranted.},\r\n project = {aaapatient},\r\n type = {1. Peer-Reviewed Journal Papers}\r\n}\r\n\r\n\n
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\n Abdominal aortic aneurysm (AAA) represents a degenerative disease process of the abdominal aorta that results in dilation and permanent remodeling of the arterial wall. A fluid structure interaction (FSI) parametric study was conducted to evaluate the progression of aneurysmal disease and its possible implications on risk of rupture. Two parametric studies were conducted using (i) the iliac bifurcation angle and (ii) the AAA neck angulation. Idealized streamlined AAA geometries were employed. The simulations were carried out using both isotropic and anisotropic wall material models. The parameters were based on CT scans measurements obtained from a population of patients. The results indicate that the peak wall stresses increased with increasing iliac and neck inlet angles. Wall shear stress (WSS) and fluid pressure were analyzed and correlated with the wall stresses for both sets of studies. An adaptation response of a temporary reduction of the peak wall stresses seem to correlate to a certain extent with increasing iliac angles. For the neck angulation studies it appears that a breakdown from symmetric vortices at the AAA inlet into a single larger vortex significantly increases the wall stress. Our parametric FSI study demonstrates the adaptation response during aneurysmal disease progression and its possible effects on the AAA risk of rupture. This dependence on geometric parameters of the AAA can be used as an additional diagnostic tool to help clinicians reach informed decisions in establishing whether a risky surgical intervention is warranted.\n
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\n\n \n \n Xenos, M.; Rambhia, S.; Alemu, Y.; Einav, S.; Labropoulos, N.; Tassiopoulos, A.; Ricotta, J. J.; and Bluestein, D.\n\n\n \n \n \n \n \n Patient-based abdominal aortic aneurysm rupture risk prediction with fluid structure interaction modeling.\n \n \n \n \n\n\n \n\n\n\n
Ann. Biomed. Eng, 38: 3323-3337. 2010.\n
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\n\n \n \n paper\n \n \n \n link\n \n \n\n \n\n \n link\n \n \n\n bibtex\n \n\n \n \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n \n \n \n\n\n\n
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@article{z43,\r\n author = {Xenos, M. and Rambhia, S. and Alemu, Y. and Einav, S. and Labropoulos, N. and Tassiopoulos, A. and Ricotta, J. J. and Bluestein, D.},\r\n year = {2010},\r\n title = {Patient-based abdominal aortic aneurysm rupture risk prediction with fluid structure interaction modeling},\r\n journal = {Ann. Biomed. Eng},\r\n volume = {38},\r\n issue = {11},\r\n pages = {3323-3337},\r\n url_Paper={/labs/dbluestein/PDF/Xenos_2010_AAA_rupture_risk.pdf},\r\n url_Link = {https://doi.org/10.1007/s10439-010-0094-3},\r\n abstract = {Elective repair of abdominal aortic aneurysm (AAA) is warranted when the risk of rupture exceeds that of surgery, and is mostly based on the AAA size as a crude rupture predictor. A methodology based on biomechanical considerations for a reliable patient-specific prediction of AAA risk of rupture is presented. Fluid-structure interaction (FSI) simulations conducted in models reconstructed from CT scans of patients who had contained ruptured AAA (rAAA) predicted the rupture location based on mapping of the stresses developing within the aneurysmal wall, additionally showing that a smaller rAAA presented a higher rupture risk. By providing refined means to estimate the risk of rupture, the methodology may have a major impact on diagnostics and treatment of AAA patients.},\r\n project = {aaapatient},\r\n type = {1. Peer-Reviewed Journal Papers}\r\n}\r\n\r\n\n
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\n Elective repair of abdominal aortic aneurysm (AAA) is warranted when the risk of rupture exceeds that of surgery, and is mostly based on the AAA size as a crude rupture predictor. A methodology based on biomechanical considerations for a reliable patient-specific prediction of AAA risk of rupture is presented. Fluid-structure interaction (FSI) simulations conducted in models reconstructed from CT scans of patients who had contained ruptured AAA (rAAA) predicted the rupture location based on mapping of the stresses developing within the aneurysmal wall, additionally showing that a smaller rAAA presented a higher rupture risk. By providing refined means to estimate the risk of rupture, the methodology may have a major impact on diagnostics and treatment of AAA patients.\n
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\n\n \n \n Rissland, P.; Alemu, Y.; Einav, S.; Ricotta, J. J.; and Bluestein, D.\n\n\n \n \n \n \n \n Abdominal aortic aneurysm risk of rupture: patient specific FSI simulations using anisotropic model.\n \n \n \n \n\n\n \n\n\n\n
J. Biomech. Eng, 131: 031001. 2009.\n
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@article{z51,\r\n author = {Rissland, P. and Alemu, Y. and Einav, S. and Ricotta, J. J. and Bluestein, D.},\r\n year = {2009},\r\n title = {Abdominal aortic aneurysm risk of rupture: patient specific FSI simulations using anisotropic model},\r\n journal = {J. Biomech. Eng},\r\n volume = {131},\r\n issue = {1},\r\n pages = {031001},\r\n url_Paper={/labs/dbluestein/PDF/Rissland_2009_AAA_rupture_risk_anisotropic.pdf},\r\n url_Link = {https://doi.org/10.1115/1.3005200},\r\n abstract = {Abdominal aortic aneurysm (AAA) rupture represents a major cardiovascular risk, combining complex vascular mechanisms weakening the abdominal artery wall coupled with hemodynamic forces exerted on the arterial wall. At present, a reliable method to predict AAA rupture is not available. Recent studies have introduced fluid structure interaction (FSI) simulations using isotropic wall properties to map regions of stress concentrations developing in the aneurismal wall as a much better alternative to the current clinical criterion, which is based on the AAA diameter alone. A new anisotropic material model of AAA that closely matches observed biomechanical AAA material properties was applied to FSI simulations of patient-specific AAA geometries in order to develop a more reliable predictor for its risk of rupture. Each patient-specific geometry was studied with and without an intraluminal thrombus (ILT) using two material models-the more commonly used isotropic material model and an anisotropic material model-to delineate the ILT contribution and the dependence of stress distribution developing within the aneurismal wall on the material model employed. Our results clearly indicate larger stress values for the anisotropic material model and a broader range of stress values as compared to the isotropic material, indicating that the latter may underestimate the risk of rupture. While the locations of high and low stresses are consistent in both material models, the differences between the anisotropic and isotropic models become pronounced at large values of strain-a range that becomes critical when the AAA risk of rupture is imminent. As the anisotropic model more closely matches the biomechanical behavior of the AAA wall and resolves directional strength ambiguities, we conclude that it offers a more reliable predictor of AAA risk of rupture.},\r\n project = {aaapatient},\r\n type = {1. Peer-Reviewed Journal Papers}\r\n}\r\n\r\n\n
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\n Abdominal aortic aneurysm (AAA) rupture represents a major cardiovascular risk, combining complex vascular mechanisms weakening the abdominal artery wall coupled with hemodynamic forces exerted on the arterial wall. At present, a reliable method to predict AAA rupture is not available. Recent studies have introduced fluid structure interaction (FSI) simulations using isotropic wall properties to map regions of stress concentrations developing in the aneurismal wall as a much better alternative to the current clinical criterion, which is based on the AAA diameter alone. A new anisotropic material model of AAA that closely matches observed biomechanical AAA material properties was applied to FSI simulations of patient-specific AAA geometries in order to develop a more reliable predictor for its risk of rupture. Each patient-specific geometry was studied with and without an intraluminal thrombus (ILT) using two material models-the more commonly used isotropic material model and an anisotropic material model-to delineate the ILT contribution and the dependence of stress distribution developing within the aneurismal wall on the material model employed. Our results clearly indicate larger stress values for the anisotropic material model and a broader range of stress values as compared to the isotropic material, indicating that the latter may underestimate the risk of rupture. While the locations of high and low stresses are consistent in both material models, the differences between the anisotropic and isotropic models become pronounced at large values of strain-a range that becomes critical when the AAA risk of rupture is imminent. As the anisotropic model more closely matches the biomechanical behavior of the AAA wall and resolves directional strength ambiguities, we conclude that it offers a more reliable predictor of AAA risk of rupture.\n
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\n\n \n \n Bluestein, D.; Dumont, K.; De Beule, M.; Ricotta, J. J.; Impellizzeri, P.; Verhegghe, B.; and Verdonck, P.\n\n\n \n \n \n \n \n Intraluminal thrombus and risk of rupture in patient specific abdominal aortic aneurysm- FSI modelling.\n \n \n \n \n\n\n \n\n\n\n
Comput Methods Biomech. Biomed. Eng, 12: 73-81. 2009.\n
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\n\n \n \n paper\n \n \n \n link\n \n \n\n \n\n \n link\n \n \n\n bibtex\n \n\n \n \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n \n \n \n\n\n\n
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@article{z52,\r\n author = {Bluestein, D. and Dumont, K. and De Beule, M. and Ricotta, J. J. and Impellizzeri, P. and Verhegghe, B. and Verdonck, P.},\r\n year = {2009},\r\n title = {Intraluminal thrombus and risk of rupture in patient specific abdominal aortic aneurysm- FSI modelling},\r\n journal = {Comput Methods Biomech. Biomed. Eng},\r\n volume = {12},\r\n issue = {1},\r\n pages = {73-81},\r\n url_Paper={/labs/dbluestein/PDF/Bluestein_2009_intraluminal_thrombus_AAA_FSI.pdf},\r\n url_Link = {https://doi.org/10.1080/10255840802176396},\r\n abstract = {Recent numerical studies of abdominal aortic aneurysm (AAA) suggest that intraluminal thrombus (ILT) may reduce the stress loading on the aneurysmal wall. Detailed fluid structure interaction (FSI) in the presence and absence of ILT may help predict AAA rupture risk better. Two patients, with varied AAA geometries and ILT structures, were studied and compared in detail. The patient specific 3D geometries were reconstructed from CT scans, and uncoupled FSI approach was applied. Complex flow trajectories within the AAA lumen indicated a viable mechanism for the formation and growth of the ILT. The resulting magnitude and location of the peak wall stresses was dependent on the shape of the AAA, and the ILT appeared to reduce wall stresses for both patients. Accordingly, the inclusion of ILT in stress analysis of AAA is of importance and would likely increase the accuracy of predicting AAA risk of rupture.},\r\n project = {aaapatient},\r\n type = {1. Peer-Reviewed Journal Papers}\r\n}\r\n\r\n\n
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\n Recent numerical studies of abdominal aortic aneurysm (AAA) suggest that intraluminal thrombus (ILT) may reduce the stress loading on the aneurysmal wall. Detailed fluid structure interaction (FSI) in the presence and absence of ILT may help predict AAA rupture risk better. Two patients, with varied AAA geometries and ILT structures, were studied and compared in detail. The patient specific 3D geometries were reconstructed from CT scans, and uncoupled FSI approach was applied. Complex flow trajectories within the AAA lumen indicated a viable mechanism for the formation and growth of the ILT. The resulting magnitude and location of the peak wall stresses was dependent on the shape of the AAA, and the ILT appeared to reduce wall stresses for both patients. Accordingly, the inclusion of ILT in stress analysis of AAA is of importance and would likely increase the accuracy of predicting AAA risk of rupture.\n
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\n\n \n \n Ricotta, J. J.; Pagan, J.; Xenos, M.; Alemu, Y.; Einav, S.; and Bluestein, D.\n\n\n \n \n \n \n \n Cardiovascular disease management: the need for better diagnostics.\n \n \n \n \n\n\n \n\n\n\n
Med Biol Eng Comput, 46: 1059-1068. 2008.\n
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\n\n \n \n paper\n \n \n \n link\n \n \n\n \n\n \n link\n \n \n\n bibtex\n \n\n \n \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n \n \n \n\n\n\n
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@article{z54,\r\n author = {Ricotta, J. J. and Pagan, J. and Xenos, M. and Alemu, Y. and Einav, S. and Bluestein, D.},\r\n year = {2008},\r\n title = {Cardiovascular disease management: the need for better diagnostics},\r\n journal = {Med Biol Eng Comput},\r\n volume = {46},\r\n issue = {11},\r\n pages = {1059-1068},\r\n url_Paper={/labs/dbluestein/PDF/Ricotta_2008_cardiovascular_disease_diagnostics.pdf},\r\n url_Link = {https://doi.org/10.1007/s11517-008-0416-x},\r\n abstract = {Current diagnostic testing for cardiovascular pathology usually rests on either physiological or anatomic measurement. Multiple tests must then be combined to arrive at a conclusion regarding treatment of a specific pathology. Much of the diagnostic decisions currently made are based on rough estimates of outcomes, often derived from gross anatomic observations or extrapolation of physical laws. Thus, intervention for carotid and coronary disease is based on estimates of diameter stenosis, despite data to suggest that plaque character and lesion anatomy are important determinants of outcome. Similarly, abdominal aortic aneurysm (AAA) intervention is based on maximal aneurysm diameter without regard for arterial wall composition or individual aneurysm geometry. In other words, our current diagnostic tests do not reflect the sophistication of our current knowledge of vascular disease. Using a multimodal approach, computer modeling has the potential to predict clinical outcomes based on a variety of factors including arterial wall composition, surface anatomy and hemodynamic forces. We term this more sophisticated approach "patient specific diagnostics", in which the computer models are reconstructed from patient specific clinical visualizing modalities, and material properties are extracted from experimental measurements of specimens and incorporated into the modeling using advanced material models (including nonlinear anisotropic models) and performed as dynamic simulations using the FSI (fluid structure interaction) approach. Such an approach is sorely needed to improve the effectiveness of interventions. This article will review ongoing work in "patient specific diagnostics" in the areas of carotid, coronary and aneurismal disease. We will also suggest how this approach may be applicable to management of aortic dissection. New diagnostic methods should allow better patient selection, targeted intervention and modeling of the results of different therapies.},\r\n project = {aaapatient},\r\n type = {1. Peer-Reviewed Journal Papers}\r\n}\r\n\r\n\n
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\n Current diagnostic testing for cardiovascular pathology usually rests on either physiological or anatomic measurement. Multiple tests must then be combined to arrive at a conclusion regarding treatment of a specific pathology. Much of the diagnostic decisions currently made are based on rough estimates of outcomes, often derived from gross anatomic observations or extrapolation of physical laws. Thus, intervention for carotid and coronary disease is based on estimates of diameter stenosis, despite data to suggest that plaque character and lesion anatomy are important determinants of outcome. Similarly, abdominal aortic aneurysm (AAA) intervention is based on maximal aneurysm diameter without regard for arterial wall composition or individual aneurysm geometry. In other words, our current diagnostic tests do not reflect the sophistication of our current knowledge of vascular disease. Using a multimodal approach, computer modeling has the potential to predict clinical outcomes based on a variety of factors including arterial wall composition, surface anatomy and hemodynamic forces. We term this more sophisticated approach \"patient specific diagnostics\", in which the computer models are reconstructed from patient specific clinical visualizing modalities, and material properties are extracted from experimental measurements of specimens and incorporated into the modeling using advanced material models (including nonlinear anisotropic models) and performed as dynamic simulations using the FSI (fluid structure interaction) approach. Such an approach is sorely needed to improve the effectiveness of interventions. This article will review ongoing work in \"patient specific diagnostics\" in the areas of carotid, coronary and aneurismal disease. We will also suggest how this approach may be applicable to management of aortic dissection. New diagnostic methods should allow better patient selection, targeted intervention and modeling of the results of different therapies.\n
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