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Multiscale Modeling of the Normal and Aneurysmatic Abdominal Aorta
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Biomechanics.
2010 (English)Licentiate thesis, comprehensive summary (Other academic)
Place, publisher, year, edition, pages
Stockholm: KTH , 2010. , 20 p.
Series
Trita-HFL. Report / Royal Institute of Technology, Solid Mechanics, ISSN 1654-1472 ; 0498
Identifiers
URN: urn:nbn:se:kth:diva-28925OAI: oai:DiVA.org:kth-28925DiVA: diva2:391077
Presentation
2010-12-20, Sal D3, Lindstedtsvägen 5, KTH, Stockholm, 10:15 (English)
Opponent
Supervisors
Note

QC 20110127

Available from: 2011-01-27 Created: 2011-01-24 Last updated: 2013-01-15Bibliographically approved
List of papers
1. Three-Dimensional Geometrical Characterization of Abdominal Aortic Aneurysms: Image-Based Wall Thickness Distribution
Open this publication in new window or tab >>Three-Dimensional Geometrical Characterization of Abdominal Aortic Aneurysms: Image-Based Wall Thickness Distribution
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2009 (English)In: Journal of Biomechanical Engineering, ISSN 0148-0731, E-ISSN 1528-8951, Vol. 131, no 6, 061015- p.Article in journal (Refereed) Published
Abstract [en]

The clinical assessment of abdominal aortic aneurysm (AAA) rupture risk is based on the quantification of AAA size by measuring its maximum diameter from computed tomography (CT) images and estimating the expansion rate of the aneurysm sac over time. Recent findings have shown that geometrical shape and size, as well as local wall thickness may be related to this risk; thus, reliable noninvasive image-based methods to evaluate AAA geometry have a potential to become valuable clinical tools. Utilizing existing CT data, the three-dimensional geometry of nine unruptured human AAAs was reconstructed and characterized quantitatively. We propose and evaluate a series of 1D size, 2D shape, 3D size, 3D shape, and second-order curvature-based indices to quantify AAA geometry, as well as the geometry of a size-matched idealized fusiform aneurysm and a patient-specific normal abdominal aorta used as controls. The wall thickness estimation algorithm, validated in our previous work, is tested against discrete point measurements taken from a cadaver tissue model, yielding an average relative difference in AAA wall thickness of 7.8%. It is unlikely that any one of the proposed geometrical indices alone would be a reliable index of rupture risk or a threshold for elective repair. Rather, the complete geometry and a positive correlation of a set of indices should be considered to assess the potential for rupture. With this quantitative parameter assessment, future research can be directed toward statistical analyses correlating the numerical values of these parameters with the risk of aneurysm rupture or intervention (surgical or endovascular). While this work does not provide direct insight into the possible clinical use of the geometric parameters, we believe it provides the foundation necessary for future efforts in that direction.

National Category
Industrial Biotechnology
Identifiers
urn:nbn:se:kth:diva-29139 (URN)10.1115/1.3127256 (DOI)000266035700015 ()19449969 (PubMedID)
Note
QC 20110127Available from: 2011-01-27 Created: 2011-01-27 Last updated: 2017-12-11Bibliographically approved
2. Micromechanical Characterization of Intra-luminal Thrombus Tissue from Abdominal Aortic Aneurysms
Open this publication in new window or tab >>Micromechanical Characterization of Intra-luminal Thrombus Tissue from Abdominal Aortic Aneurysms
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2010 (English)In: Annals of Biomedical Engineering, ISSN 0090-6964, E-ISSN 1573-9686, Vol. 38, no 2, 371-379 p.Article in journal (Refereed) Published
Abstract [en]

The reliable assessment of Abdominal Aortic Aneurysm rupture risk is critically important in reducing related mortality without unnecessarily increasing the rate of elective repair. Intra-luminal thrombus (ILT) has multiple biomechanical and biochemical impacts on the underlying aneurysm wall and thrombus failure might be linked to aneurysm rupture. Histological slices from 7 ILTs were analyzed using a sequence of automatic image processing and feature analyzing steps. Derived microstructural data was used to define Representative Volume Elements (RVE), which in turn allowed the estimation of microscopic material properties using the non-linear Finite Element Method. ILT tissue exhibited complex microstructural arrangement with larger pores in the abluminal layer than in the luminal layer. The microstructure was isotropic in the abluminal layer, whereas pores started to orient along the circumferential direction towards the luminal site. ILT's macroscopic (reversible) deformability was supported by large pores in the microstructure and the inhomogeneous structure explains in part the radially changing macroscopic constitutive properties of ILT. Its microscopic properties decreased just slightly from the luminal to the abluminal layer. The present study provided novel microstructural and micromechanical data of ILT tissue, which is critically important to further explore the role of the ILT in aneurysm rupture. Data provided in this study allow an integration of structural information from medical imaging for example, to estimate ILT's macroscopic mechanical properties.

Keyword
Intra-luminal thrombus, Abdominal Aortic Aneurysm (AAA), Finite element, method (FEM), Microscale, Constitutive modeling, wall stress, rupture
National Category
Medical Laboratory and Measurements Technologies
Identifiers
urn:nbn:se:kth:diva-19175 (URN)10.1007/s10439-009-9837-4 (DOI)000274237000013 ()2-s2.0-77249089737 (Scopus ID)
Funder
Swedish Research Council, 2006-7568
Note
QC 20110124Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
3. A constitutive model for vascular tissue that integrates fibril, fiber andcontinuum levels
Open this publication in new window or tab >>A constitutive model for vascular tissue that integrates fibril, fiber andcontinuum levels
2010 (English)Report (Other academic)
Abstract [en]

A fundamental understanding of the mechanical properties of the extracellular matrix (ECM) is critically important to quantify the amount of macroscopic stress and/or strain transmitted to the cellular level of vascular tissue. Structural constitutive models integrate histological and mechanical information, and hence, allocate stress and strain to the different micro-structural components of the vascular wall. The present work proposes a novel multi-scale structural constitutive model for passive vascular tissue, where collagen fibers are assembled by proteoglycan (PG) cross-linked collagen fibrils and reinforce an otherwise isotropic matrix material. Multiplicative kinematics account for straightening and stretching of collagen fibrils and an orientation density function captures the spatial organization of collagen fibers in the tissue. Mechanical and structural assumptions at the collagen fibril level define a piece-wise analytical stress-stretch response of collagen fibers, which in turn is integrated over the unit sphere to constitute the tissue’s macroscopic mechanical properties. The proposed model displays salient macroscopic feature of vascular tissue, and employs material and structural parameters of clear physical meaning. Model parameters were estimated from meanpopulation data of the normal and aneurysmatic aortic wall and used to predict in-vivo stress states of patient-specific vascular geometries, thought to demonstrate the robustness of the particular Finite Element (FE) implementation. The collagen fibril level of the multi-scale constitutive formulation provides an interface to integrate vascular wall biology and to account for collagen turn-over for example.

Place, publisher, year, edition, pages
Stockholm: KTH, 2010
Series
Trita-HFL, ISSN 1104-6813 ; 497
Identifiers
urn:nbn:se:kth:diva-29140 (URN)
Note
QC 201101Available from: 2011-01-27 Created: 2011-01-27 Last updated: 2011-01-27Bibliographically approved

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