Evaluating the Effect of the Number of Wire of Flow Diverter Stents on the Nonstagnated Region Formation in an Aneurysm Sac Using Lagrangian Coherent Structure and Hyperbolic Time Analysis

Abstract

Giant aneurysms at carotid arteries are typically treated with flow diverter (FD) stents in the clinic. Although the goal of an FD stent is to direct most of the blood flow into the main artery, not much is known regarding the effects of wire number an FD possesses on the hemodynamics inside the aneurysm. In this study, 48-, 72-, and 96-wire FD stents were separately implanted into the site of aneurysm of a 45-year-old woman to evaluate the effects of the FD's number of wires on fluid flow behavior in the aneurysm sac. Time evolution of both finite-time Lyapunov exponent (FTLE) and hyperbolic time fields in the aneurysm sac were calculated by using computational fluid dynamics along with Lagrangian coherent structure (LCS) methods. The computations reveal that a 48-wire FD stent allows a large amount of blood to enter inside the aneurysm sac revealing scattered nonstagnant flow zones formation. Besides, time-dependent results of LCS analysis show that most of the blood flow is diverted into the main artery when 72- and 96-wire number Surpass brand FD stents are separately implanted into the site of the aneurysm, yielding a small amount of blood flow to penetrate into the aneurysm sac. Furthermore, FTLE and hyperbolic time field plots are in good agreement with the patient's digital subtraction angiography image captured 3.5 minutes after 72-wire Surpass brand FD stent implantation.