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Noninvasive Biomechanical Assessment of the Rupture Potential of Abdomial Aortic Aneurysm

Wang, Hong Jun (2002) Noninvasive Biomechanical Assessment of the Rupture Potential of Abdomial Aortic Aneurysm. Doctoral Dissertation, University of Pittsburgh.

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PDF (Noninvasive Biomechanical Assessment of the Rupture Potential of Abdominal Aortic Aneurysms) - Primary Text
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    Image (GIF) (Figure 1 - An artist's rendering of a AAA in its in situ position) - Supplemental Material
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      PDF (Figure 17 - An excised AAA from an autopsy sample (htttp://www.vascularsurgery.com)) - Supplemental Material
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        PDF (Figure 2 - Illustration of the traditional open AAA surgical procedure) - Supplemental Material
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          PDF (Figure 23 - The "Virtual AAA" with a constant, patient specific wall thickness and included ILT) - Supplemental Material
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            PDF (Figure 25 - Comparison of 3-D wall stress distribution between AAA models with and without ILT. The individual color scales to the right indicate von Mises stress. Both the posterior and anterior views are shown for each case) - Supplemental Material
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              PDF (Figure 27 - Von Mises stress for the case for which Ω0 was loaded (i.e., step A-C in Figure 26, or the true stress distribution) and for the case which ΩCT was assumed stress free and loaded (i.e., step B-D in Figure 26, as was done in this work)) - Supplemental Material
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                PDF (Figure 28 - Structure of the normal artery (http://www.heartcenteronline.com)) - Supplemental Material
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                  PDF (Figure 3 - Illustration of minimally invasive endovascular repair of AAA) - Supplemental Material
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                    PDF (Figure 31 - Immunohistochemistry staining on wall specimen section from thick ILT group (A and D), thin ILT group (B and E), and primary-deleted negative control (C and F)) - Supplemental Material
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                      PDF (Figure 32 - Neovascularization in wall with adjacent thick ILT, thin ILT, and nonaneurysmal control. New vessels were identified via staining for von Willebrand factor, which is a protein marker for endothelial cells. Figure from Vorp et al. [183]) - Supplemental Material
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                        PDF (Figure 35 - ILT Thickness/Local Diameters) - Supplemental Material
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                          Image (GIF) (Figure 4 - A cross-sectional view of a typical intraluminal thrombus specimen) - Supplemental Material
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                            PDF (Figure 58 - Local wall strength distribution estimated by using the developed statistical model (equation 8.16) for all four AAA studied) - Supplemental Material
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                              PDF (Figure 59 - Local ILT thickness distribution for the four AAA studied) - Supplemental Material
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                                PDF (Figure 60 - Local diameter distribution for the four AAA studied) - Supplemental Material
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                                  PDF (Figure 62 - RPI distribution of the four AAA evaluated in this study) - Supplemental Material
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                                    PDF (Figure 63 - von Mises stress distribution (top) and maximum principal stress distribution (bottom) on AAA #4. Note the similarity between the two stress distribution patterns) - Supplemental Material
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                                      Abstract

                                      Abdominal aortic aneurysm (AAA) is a localized dilation of the infrarenal aorta. Ruptured AAA has a mortality rate of 95% and is ranked as the 13th leading cause of death in the US. The ability to reliably evaluate the susceptibility of a particular AAA to rupture could vastly improve the clinical management of AAA patients. Currently, no such reliable evaluation technique exists. The purpose of this work was to develop a noninvasive technique to evaluate the rupture potential of individual AAA.To predict the wall strength distribution, experimentally determined wall strength data were used for construction of a mathematical model using multiple linear regression techniques. The developed model was then validated using data from a different group of specimens. The strength distributions for four different AAA were then generated using the validated model. The finite element method was used to estimate the wall stress distribution for all four AAA based on their realistic geometries (reconstructed from CT images) which included intraluminal thrombus (ILT). The measured systolic blood pressure was applied as the loading condition. Nonlinear hyperelastic constitutive models for AAA and ILT tissue were used, the latter being developed here based on uniaxial tensile testing data. For each patient, a local Rupture Potential Index (RPI) distribution was calculated as local (nodal) wall stress divided by local wall strength. The developed model contains four independent variable parameters: AAA size, patient's age, family history, local ILT thickness, and normalized local AAA diameter (R Squared = 0.86, p = 0.001). The model predicted the actual (measured) strength very accurately (R Squared = 0.81 for model validation). The wall strength values predicted for the four AAA studied ranged from 130 to 306 N/(cm squared), whereas the measured wall strength values ranged from 39 to 324 N/(cm squared). The peak wall stress for the four AAA studied ranged from 19 to 37 N/(cm squared). The peak RPI values ranged from 0.15 to 0.55. This patient-specific, computer-based, noninvasive RPI estimation technique could become an import and reliable diagnostic tool for AAA patient management. However, further clinical studies are needed to validate this technique.


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                                      Item Type: University of Pittsburgh ETD
                                      Creators/Authors:
                                      CreatorsEmailORCID
                                      Wang, Hong Jundwang@cardiacassist.com
                                      ETD Committee:
                                      ETD Committee TypeCommittee MemberEmailORCID
                                      Committee ChairVorp, David A.vorpda@msx.upmc.edu
                                      Committee MemberRobertson, Anne M.annerob@engrng.pitt.edu
                                      Committee MemberBorovetz, Harvey S.borovetzhs@msx.upmc.edu
                                      Committee MemberWebster, Marshall W.webstermw@msx.upmc.edu
                                      Committee MemberSacks, Michael S.msacks@pitt.edu
                                      Title: Noninvasive Biomechanical Assessment of the Rupture Potential of Abdomial Aortic Aneurysm
                                      Status: Unpublished
                                      Abstract: Abdominal aortic aneurysm (AAA) is a localized dilation of the infrarenal aorta. Ruptured AAA has a mortality rate of 95% and is ranked as the 13th leading cause of death in the US. The ability to reliably evaluate the susceptibility of a particular AAA to rupture could vastly improve the clinical management of AAA patients. Currently, no such reliable evaluation technique exists. The purpose of this work was to develop a noninvasive technique to evaluate the rupture potential of individual AAA.To predict the wall strength distribution, experimentally determined wall strength data were used for construction of a mathematical model using multiple linear regression techniques. The developed model was then validated using data from a different group of specimens. The strength distributions for four different AAA were then generated using the validated model. The finite element method was used to estimate the wall stress distribution for all four AAA based on their realistic geometries (reconstructed from CT images) which included intraluminal thrombus (ILT). The measured systolic blood pressure was applied as the loading condition. Nonlinear hyperelastic constitutive models for AAA and ILT tissue were used, the latter being developed here based on uniaxial tensile testing data. For each patient, a local Rupture Potential Index (RPI) distribution was calculated as local (nodal) wall stress divided by local wall strength. The developed model contains four independent variable parameters: AAA size, patient's age, family history, local ILT thickness, and normalized local AAA diameter (R Squared = 0.86, p = 0.001). The model predicted the actual (measured) strength very accurately (R Squared = 0.81 for model validation). The wall strength values predicted for the four AAA studied ranged from 130 to 306 N/(cm squared), whereas the measured wall strength values ranged from 39 to 324 N/(cm squared). The peak wall stress for the four AAA studied ranged from 19 to 37 N/(cm squared). The peak RPI values ranged from 0.15 to 0.55. This patient-specific, computer-based, noninvasive RPI estimation technique could become an import and reliable diagnostic tool for AAA patient management. However, further clinical studies are needed to validate this technique.
                                      Date: 30 August 2002
                                      Date Type: Completion
                                      Defense Date: 17 July 2002
                                      Approval Date: 30 August 2002
                                      Submission Date: 24 June 2002
                                      Access Restriction: No restriction; The work is available for access worldwide immediately.
                                      Patent pending: No
                                      Institution: University of Pittsburgh
                                      Thesis Type: Doctoral Dissertation
                                      Refereed: Yes
                                      Degree: PhD - Doctor of Philosophy
                                      URN: etd-06242002-114810
                                      Uncontrolled Keywords: 3D Reconstruction; Abdominal Aortic Aneurysm; Biomechanics; Finite Element Method; Hyperelastic; Intraluminal Thrombus; Microstructure; Cardiovascular Disease; Multiple Linear Regression
                                      Schools and Programs: Swanson School of Engineering > Bioengineering
                                      Date Deposited: 10 Nov 2011 14:48
                                      Last Modified: 19 Jun 2012 11:58
                                      Other ID: http://etd.library.pitt.edu:80/ETD/available/etd-06242002-114810/, etd-06242002-114810

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