ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

3D OPTICAL RECONSTRUCTION TECHNIQUE FOR BALLOON
EXPANDABLE STENT CHARACTERISATION
I.Zwierzak 1 , J.W.Fenner 2 , A.J.Narracott 3
ABSTRACT
Balloon angioplasty with stenting is a commonly used interventional procedure to treat
stenotic arteries. Clinical studies have examined the relationship between vascular
injury considering both stent design and the symmetry of stent deployment. Stent
deployment provokes a biological response (proliferation of smooth muscle cells),
which leads to neointimal tissue growth, resulting in restenosis of the vascular lesion.
This study presents experimental characterisation of balloon expandable stent
deployment. A non-contact stereo-photogrammetric method was used to determine
stent deformation during balloon inflation using a clinical implantation device. Two
stereoscopically positioned high resolution cameras were used to record the expansion
process. Three dimensional reconstruction of strut separation was undertaken using
stereo image pairs. The results demonstrate that local variations are observed in the
deformation of stent cell geometry at either end of the stent despite similar global
deformation, as assessed by changes in stent diameter. This may have implications for
the local strains generated during contact of the stent with the vessel wall.
INTRODUCTION
Cardiovascular diseases (CVD) cause approximately half of all deaths in Europe [1].
Atherosclerosis is one of the most common of such diseases. It causes stenosis in
arteries that supply blood to the heart [2]. Non-invasive treatment such as angioplasty
with stenting is commonly used to restore normal blood flow in coronary arteries and
prevent heart attacks [2]. Nevertheless, in-stent restenosis after coronary intervention
still remains an unsolved and important clinical problem due to neointimal hyperplasia
in response to stent deployment and vessel wall injury [3]. It has been suggested that the
degree of restenosis is related to the magnitude of the strains during stent implantation,
due to the resulting vascular injury [3].
Computational simulations are often used to characterise stent expansion, with
applications including stent interaction with a stenosed artery [4] and stent flexibility in
curved vessels [5]. Detailed study of such problems can be difficult to achieve with
clinical or experimental studies. However, the results of computational simulations need
to be validated with experimental data.
For experimental investigation of stent expansion a non-contact system is desirable due
to the small scales involved and the delicate nature of the stent structure. Previous
experimental studies have used optical methods to examine two dimensional (2D)
global characterisation of stent expansion, with focus on changes in stent diameter and
length with increasing balloon pressure [6, 7]. Kiousis et al. [8] reported 2D
experimental measurement of free expansion of six vascular stents and provided
comparisons with a computational model. This study described three components of the
expansion process: foreshortening, maximum dog-boning and elastic recoil.
1 PhD student, Department of Cardiovascular Science, University of Sheffield, Faculty of Medicine,
Dentistry and Health, Beech Hill Road, Parks Road, Sheffield, S10 2RX, UK
2 Department of Cardiovascular Science, University of Sheffield, Faculty of Medicine, Dentistry and
Health, Beech Hill Road, Parks Road, Sheffield, S10 2RX, UK
3 Department of Cardiovascular Science, University of Sheffield, Faculty of Medicine, Dentistry and
Health, Beech Hill Road, Parks Road, Sheffield, S10 2RX, UK