Measuring arterial strain induced by endovascular stents

Endovascular stents are expandable, fenestrated tubes that are threaded in their collapsed state through an artery to a site of occlusion, plastically enlarged and left as permanent implants to scaffold the artery open. The s tent induces large-scale vascular strains that are difficult to measure in vivo and yet can be critical determinants of stent-vessel biology. A method is developed to measure the strain tensor developed on the surface of an a rtery as a stent is expanded in vivo. Arterial sections are marked with ref erence points and imaged as the stent is expanded. An axially symmetric par ametric model of the artery is determined for each expansion timepoint, and these reference points are backprojected onto this surface. The backprojec ted reference points are grouped and analysed to determine the circumferent ial, axial and torsional strain tensor components in each arterial subsecti on. The method is characterised in vitro using bovine artery segments and a latex phantom, and is then tested on rabbits to demonstrate its feasibilit y in vivo. In vitro experiments on stented bovine arteries show typical pos t-stenting strains of 0.60, -0.26, and 0.08 mm mm(-1) in the circumferentia l, axial and torsional directions, respectively, sampled every 1 mm along t he length of the stented region. Phantom experiments characterise the RMS e rror of system measurements as 0.1 mm mm(-1) The system is shown capable of measuring strains of straight, accessible vessels in the presence of respi ratory/cardiac motion and visual glare in vivo.