Vortex dynamics and transport phenomena in stenotic aortic models using Echo-PIV

Abstract

Atherosclerosis is the most fatal cardiovascular disease. As disease progresses, stenoses grow inside the arteries blocking their lumen and altering blood flow. Analysing flow dynamics can provide a deeper insight on the stenosis evolution. In this work we combined Eulerian and Lagrangian descriptors to analyze blood flow dynamics and fluid transport in stenotic aortic models with morphology, mechanical and optical properties close to those of real arteries. To this end, vorticity, particle residence time (PRT), particle's final position (FP) and finite time Lyapunov's exponents (FTLE) were computed from the experimental fluid velocity fields acquired using ultrasonic particle imaging velocimetry (Echo-PIV). For the experiments, CT-images were used to create morphological realistic models of the descending aorta with 0%, 35% and 50% occlusion degree with same mechanical properties as real arteries. Each model was connected to a circuit with a pulsatile programmable pump which mimics physiological flow and pressure conditions. The pulsatile frequency was set to ≈0.9 Hz (55 bpm) and the upstream peak Reynolds number (Re) was changed from 1100 to 2000. Flow in the post-stenotic region was composed of two main structures: a high velocity jet over the stenosis throat and a recirculation region behind the stenosis where vortex form and shed. We characterized vortex kinematics showing that vortex propagation velocity increases with Re. Moreover, from the FTLE field we identified Lagrangian coherent structures (i.e. material barriers) that dictate transport behind the stenosis. The size and strength of those barriers increased with Re and the occlusion degree. Finally, from the PRT and FP maps, we showed that independently of Re, the same amount of fluid remains on the stenosis over more than a pulsatile period.

Experimental Validation of a Novel Solid-Liquid Swirling Flow Reactor for Dense Suspensions

“…It acquires images using an ultrasound transducer and yields velocity fields from these images with similar processing algorithms to PIV. The most common field of application is the medical field, where optical access to arteries is not feasible, and ultrasound imaging devices are commonly used instead [21,22]. The Signalto-Noise-Ratio (SNR) and resolution are relatively low for UIV compared to PIV, and the resolution differs between the parallel and perpendicular direction to the transducer [17].…”

Comparing flow in helical and straight stents using 2D ultrasound particle image velocimetry

“…To test this hypothesis, models of stented arteries, with helical or straight stents, were created and flow was observed in their inlet and outlet for several cardiac cycles using 2D ultrasound particle image velocimetry (PIV), i.e., echo-PIV. 7,8 Even though swirling flow cannot be directly studied using 2D ultrasound imaging-due to being a 3D phenomenon and having out-of-plane velocity components-its signatures may be measurable in the outlet of the helical model. The straight model serves as the control case and several comparisons are made to see how the flow in the outlet of the helical model differs from its own inlet and the outlet of the straight model.…”

Obtaining Vortex Formation in Blood Flow by Particle Tracking: Echo-PV Methods and Computer Simulation

“…Since the complex models of local hemodynamics usually contain a number of empirical coefficients, in vitro experiments of model verification are necessary. For this purpose, optical particle velocimetry (PV) [37][38][39][40][41][42] and ultrasonic PV (Echo-PV) [43,44] technologies are widely used. The optical PV method operates with a fine contrast impurity (polystyrene, polyamide, or glass beads with size 0.2-100 µm).…”