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Computer Aided Angioplasty: Patient-specific arterial modeling and smooth 3D contact analysis of the stent-balloon-artery interaction
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
2006 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

Paper A: In this paper, the development and implementation of a contact algorithm based on C2-continuous surface representations is discussed. In 3D contact simulations involving models with arbitrarily curved surfaces (as in the case of vessel walls), the discretization of the contact surfaces by means of facet-based techniques could lead to numerical instabilities and finally loss of quadratic convergence. These instabilities arise mainly due to the sliding of contractor (slave) nodes over the boundaries of target (master) contact facets, where jumps of the normal vector are experienced. The paper addresses successfully this problem, by discretization of the target surfaces by means of C2-continuous parameterization schemes. Initially, the uniform cubic B-spline surfaces are introduced. Next, in an attempt for more accurate representations of the geometric models of the contact surfaces, a new parameterization based on the expression of cubic B-splines is developed. The two approaches are implemented into a finite element framework and more specifically, into the multipurpose finite element analysis program FEAP. The special merits of the developed algorithms and the advantages of the smooth surfaces over facet-based approaches are exhibited through a classical contact mechanics problem, considering incompressibility, finite deformations and large slidings. Next, a simulation of balloon angioplasty with stenting is presented, where the contact between both medical devices (balloon and stent) with the arterial wall is modeled. The arterial wall is modeled in this first approach, as hyperelastic, homogeneous, isotropic, while a cylindrically orthotropic model is developed to capture the nonlinear, anisotropic behavior of the balloon catheter under pressure. Two stents with the same geometry but different strut thickness, are studied. Both are considered elasto-plastic. The performed simulations point out the outcome of the balloon angioplasty and stenting in terms of luminal gain and mechanical strains. Finally, a comparison between the two stent configurations is presented.

Paper B: The second paper makes use of the contact tool developed in Paper A and focuses on the changes of the mechanical environment of the arterial wall due to stenting, as a function of a set of stent design parameters. In particular, Paper B presents a detailed geometric and material model of a postmortem human iliac artery, composed by distinct tissue components, each associated with specific mechanical properties. The constitutive formulation for the artery considers anisotropic, highly nonlinear mechanical characteristics under supraphysiological loadings. The material and structural parameters of the arterial model are obtained through uniaxial tensile tests on stripes extracted from the several arterial tissues that form the stenosis, axially and circumferentially oriented. Through cooperation with a well-established stent manufacturing company, an iliac stent was acquired. The dimensions of the stent are measured under a reflected-light microscope, while it is parameterized in such a way as to enable new designs to be simply generated through variations of its geometric parameters. The 3D balloon-stent-artery interaction is simulated by making use of the smooth contact surfaces with C2-continuity, as previously mentioned. Next, scalar quantities attempt to characterize the arterial wall changes after stenting, in form of contact forces induced by the stent struts, stresses within the individual components and luminal change. These numerically derived quantities allow the determination of the most appropriate stent configuration for an individual stenosis. Therefore, the proposed methodology has the potential to provide a scientific basis for optimizing treatment procedures, stent material and geometries on a patient-specific level.

Place, publisher, year, edition, pages
Stockholm: KTH , 2006. , 18 p.
Series
Trita-HFL. Report / Royal Institute of Technology, Solid Mechanics, ISSN 1654-1472 ; 0428
Keyword [en]
Contact, continuous surfaces, B-splines, balloon angioplasty, stenting, FEM
National Category
Industrial Biotechnology
Identifiers
URN: urn:nbn:se:kth:diva-4263OAI: oai:DiVA.org:kth-4263DiVA: diva2:11519
Presentation
2007-01-26, 2, D, Lindstedtsvägen 5, KTH, Stockholm, 10:15
Opponent
Supervisors
Note

QC 20101118

Available from: 2007-01-11 Created: 2007-01-11 Last updated: 2013-01-15Bibliographically approved
List of papers
1. Smooth contact strategies with emphasis on the modeling of balloon angioplasty with stenting
Open this publication in new window or tab >>Smooth contact strategies with emphasis on the modeling of balloon angioplasty with stenting
2008 (English)In: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 75, no 7, 826-855 p.Article in journal (Refereed) Published
Abstract [en]

Critical to the simulation of balloon angioplasty is the modeling of the contact between the artery wall and the medical devices. In standard approaches, the 3D contact surfaces are described by means of C0-continuous facet-based techniques, which may lead to numerical problems. This work introduces a novel contact algorithm where the target surfaces are described by polynomial expressions with C2-continuity. On the basis of uniform cubic B-splines, two different parametrization techniques are presented and compared, while the related implementation of the algorithm into a finite element analysis program is described. Two numerical examples are selected to demonstrate the special merits of the proposed contact formulation. The first example is a benchmark contact problem selected to point out the special features of the proposed strategies. The second example is concerned with the simulation of balloon angioplasty and stenting, where the contact between the balloon, the stent and the artery wall is numerically modeled. A patient-specific 3D model of a stenotic femoral artery serves as a basis. The study concludes by identifying the changes in the mechanical environment of the artery in terms of contact forces and strains by considering two different stent designs.

Keyword
B-spline, Balloon angioplasty, Contact mechanics, Smooth surfaces, Stent
National Category
Industrial Biotechnology
Identifiers
urn:nbn:se:kth:diva-6726 (URN)10.1002/nme.2277 (DOI)000258874000005 ()2-s2.0-50449090551 (Scopus ID)
Note
QC 20101118. Uppdaterad från Manuskript till Artikel (20101118).Available from: 2007-01-11 Created: 2007-01-11 Last updated: 2010-11-18Bibliographically approved
2. A numerical model to study the interaction of vascular stents with human atherosclerotic lesions
Open this publication in new window or tab >>A numerical model to study the interaction of vascular stents with human atherosclerotic lesions
2007 (English)In: Annals of Biomedical Engineering, ISSN 0090-6964, E-ISSN 1573-9686, Vol. 35, no 11, 1857-1869 p.Article in journal (Refereed) Published
Abstract [en]

A methodology is proposed that identifies optimal stent devices for specific clinical criteria. It enables to predict the effect of stent designs on the mechanical environment of stenotic arteries. In particular, we present a numerical study which is based on the interaction of a vascular stent with a patient-specific, atherosclerotic human iliac lesion of type V. The stress evolution in four different tissue components during and after stenting is investigated. The geometric model of the artery is obtained through MRI, while anisotropic material models are applied to describe the behavior of tissues at finite strains. In order to model the observed fissuring and dissection of the plaque under dilation, the undeformed configuration of the arterial wall incorporates two initial tears. The 3D balloon-stent-artery interaction problem is modeled by means of a contact algorithm, which is based on a C-2-continuous surface parametrization, hence avoiding numerical instabilities of standard facet-based techniques. In the simulations three different stent designs are studied. The performance of each stent is characterized by scalar quantities relating to stress changes in the artery, contact forces, and changes in lumen area after stenting. The study concludes by suggesting two optimal stent designs for two different clinically relevant parameters.

Keyword
atherosclerosis, balloon angioplasty, contact, finite element method, mechanical stress, modeling, MRI, stent, balloon-expandable-stent, finite-element-analysis, drug-eluting stents, intravascular ultrasound, mechanical-properties, tissue-components, wall mechanics, human arteries, angioplasty, vessel
National Category
Industrial Biotechnology
Identifiers
urn:nbn:se:kth:diva-17060 (URN)10.1007/s10439-007-9357-z (DOI)000250372400002 ()2-s2.0-35548954226 (Scopus ID)
Note
QC 20100525. Titeln ändrad från "Effects of stent design on the mechanical environment of stenotic arteries: A numerical study based on the interaction of a vascular stent with a human atherosclerotic lesion of type V".Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved

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