A low-cost and compact experimental set-up for Particle Tracking Velocimetry on realistic phantoms of coronary arteries

Coronary arteries are responsible for delivering blood to the myocardium and therefore are of vital importance. Coronary arteries are prone to atherosclerosis, which is a chronic inflammatory disease of the arterial wall that progressively reduces the lumen size as a consequence of plaque formation. The so-called ‘‘hemodynamic hypothesis” suggests that local hemodynamics is a main factor of the onset and progression of atherosclerotic lesions at coronary arteries. This thesis project is focused on the in vitro quantitative evaluation of the local hemodynamics arising within realistic coronary artery phantoms. In the present thesis, the results of two optical velocity measurement techniques, Particle Tracking Velocimetry (PTV) and Particle Image Velocimetry (PIV), are compared in a phantom (scale 1:1) of the left circumflex coronary artery (LCX). PTV shares with PIV the same experimental set-up. Both techniques are based upon the evaluation of the displacement and velocity of particles seeded in a mixture of glycerol in water, mimicking the rheological properties of blood. The exploited tracers are polyamide particles with a diameter of 60 μm, are illuminated with a continuous wave laser of 30 mW and imaged by a smartphone Samsung Galaxy S9+ with a frame rate of 960 Hz allowing time-resolved measurements with a low-cost yet reliable equipment. A centrifugal pump is used to impose a controlled flow rate at values clinically found in vivo in coronary arteries. The main difference between PIV and PTV is that if in PIV the average displacement of sub-domains of the acquired images is evaluated leading to a Eulerian motion field, in PTV single particles are individually followed over time, thus performing a Lagrangian description of the flow. The same raw images are processed with PTV and PIV to compare the two techniques. The PIV velocity fields are computed with the MATLAB® toolbox PIVlab, while single particles trajectories are evaluated on MATLAB® with a specific code. Then, a post-processing phase is carried out to evaluate the Lagrangian velocity and acceleration of the single particles and to obtain the time-averaged Eulerian field for the comparison with PIV results. The results show approximately the same time-averaged velocity fields between PIV and PTV, although the standard deviation of the velocity measured with PTV can be lower as compared to the PIV. In addition, PTV results can be used to retrieve more information such as flow acceleration which represents one of the main outcomes of the measurements with the low-cost system with the smartphone as imaging device. The findings of the present study demonstrate that the proposed low-cost system provides reliable velocity fields for both velocity measurement techniques, PIV (as previously demonstrated) and PTV. The resolution is sufficient to capture the main coronary hemodynamic features. The system presented in this thesis offers the advantage of a very low cost and can be adopted for flow experiments in the biomedical field.