Comparing Flow in Helical and Straight Stents Using 2D Ultrasound Particle Image Velocimetry

Most cases of cardiovascular diseases, including peripheral arterial disease (PAD) in the lower limb, could be prevented by a healthy diet and refrainment from smoking. Yet, stent placement is the primary course of treatment to alleviate advanced symptoms of stenosis in the superficial femoral artery (SFA) for people who have already developed PAD. It has been observed that normal stents, which are straight in shape, prevent the naturally-occurring swirling flow to form inside the SFA. Recently, a 3D helical stent has been developed for the SFA, with the assumption that the helical shape would induce swirling flow inside the artery. Swirling flow, in turn, could promote higher wall-shear stress and enhance the durability of the treatment. The aim of this study is to investigate the effects of the helical stent on flow in an in-vitro setup, using contrast-enhanced 2D ultrasound Particle Image Velocimetry (PIV) or echo-PIV. As swirling flow is a three-dimensional phenomenon with out-of-plane velocity components, the focus is on finding its signatures in the 2D ultrasound images taken from the helical stent outlet in lieu of imaging the swirling flow itself. Therefore, the regions of interest are the intel and outlet of straight and helical models, where the main analysis is done. Initial experiments and the ensuing analysis show that vector complexity and maximum vorticity are significantly higher in the outlet of the helical model, when compared to its own inlet or the outlet of the straight model. These measures serve as indicators of swirling flow in the helical stent. The implications of these results must be further investigated in patients and whether or how they may benefit them.