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TECHNICAL PAPERS: Soft Tissue

Changes in the Mechanical Environment of Stenotic Arteries During Interaction With Stents: Computational Assessment of Parametric Stent Designs

[+] Author and Article Information
Gerhard A. Holzapfel, Michael Stadler, Thomas C. Gasser

Institute for Structural Analysis, Computational Biomechanics, Graz University of Technology, 8010 Graz, Schiesstattgasse 14-B, Austria

J Biomech Eng 127(1), 166-180 (Mar 08, 2005) (15 pages) doi:10.1115/1.1835362 History: Received January 07, 2004; Revised September 09, 2004; Online March 08, 2005
Copyright © 2005 by ASME
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References

Figures

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Three different stent geometries described by a number of (geometrical) parameters, denoted by lowercase letters (upper panels). The cell types are based on products that are (or were) available commercially: (a) Multi-Link Tetra™ stent (Guidant): S1, (b) NIROYAL™-Elite stent (Boston-Scientific): S2, (c) InFlow-Gold-Flex™ stent (InFlow Dynamics): S3. The lower panels show the generated 3D views of the different stents
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Mismatch ΔM=D−M between the smallest lumen diameter M in the stenosis and the diameter D of the expanded stent. The lumen diameter of the healthy arterial region is characterized by L̄
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Circumferential Cauchy stress distributions in the arterial wall before (a), and after stenting for stent S1 at ΔM=3.6 (b). The only load applied in both configurations is the mean arterial pressure of 100.0 (mmHg). Stresses are projected onto cutting planes at x=2.0 (mm), and z=12.0 (mm),z=20.0 (mm),z=18.0 (mm). The cutting planes were selected at locations, where changes in stress due to stenting are most pronounced
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Influence of mismatch ΔM=D−M and the different stent geometries S1, S2, S3 on the three indicators D1,D2,LG. Solid lines indicate the “original strut thickness” (orig st). Dashed lines indicate the results obtained by reducing the strut thickness for the entire stent by a half (half st). A particular value of mismatch for a specific stent is indicated by a circle, which is filled or partly filled. For each stent type, arrows indicate the change from “orig st” to “half st”-data at ΔM=4.6
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Sections of the analyzed external iliac artery. Section B-B is the region with the smallest lumen diameter of 1.4 (mm). The tissue components are: adventitia (A), nondiseased media (M-nos), nondiseased intima (I-nos), fibrous cap (I-fc), lipid pool (I-lp), calcification (I-c), fibrotic intima at the medial border (I-fm) and diseased media (M-f). The regions for the analysis of edge effects, as described in Sec. 3.2.2, are denoted by the areas with dotted frames (Section D-D)
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Cells at both ends of the stent, indicated by the dimension d (see Fig. 2), in which the strut thickness st is reduced to 50% of its original value [st=225 (μm)]. Finite element meshes and geometrical data for all other cells remain at their original values
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Influence of mismatch ΔM=D−M and the different stent geometries S1, S2, S3 on the three indicators D1,D2,LG. Only the finite elements inside the dotted frames, as defined in Section D-D of Fig. 5, were considered for the computation of the indicators. Solid lines indicate the “original strut thickness” (orig st), as in Fig. 5. Dashed lines indicate the results obtained by reducing the strut thickness for the end cells of the stent by a half (half st). For each stent type, arrows indicate the change from “orig st” to “half st”-data at ΔM=4.6
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Influence of mismatch ΔM=D−M and the modified geometries of stents S1, S2, S3 on the three indicators D1,D2,LG. Solid lines indicate the “original cell geometry” (orig cg), as in Fig. 5. Dashed lines indicate the results by modifying the cell geometry (modif cg). The original width d of all stent cells (see Fig. 2) is increased by 30%. For each stent type, arrows indicate the change from “orig cg” to “modif cg”-data at ΔM=4.6
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Computation of the contact pressure for a stent strut: (a) Intimal surface with contact forces F1 and F2 at both ends of the strut, (b) equivalent trapeziform distributed load along the strut length ls, and (c) contact force q̄j per unit length acting on element j

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