In vitro and in silico fluid mechanics characterization of realistic phantoms of coronary arteries.

The present thesis work aims to investigate and analyze the results obtained from the implementation of a low-cost set-up to perform PIV analyzes. This test-bench consists of an optimization of the one proposed in the Artery in Microgravity (AIM) project, that aims to investigate the effects of microgravity on coronary haemodynamics. The data acquired from the performed experiments were analyzed with two different algorithms, PIVlab and Optical flow (OF), in order to be able to make a comparison between the two methods. The coronary artery phantoms reproducing a healthy condition and a stenotic one were individually inserted into the hydraulic circuit. The phantoms were perfused with a blood mimicking fluid (33% v/v glycerol and distilled water) with the use of a continuous flow pump. The blood mimicking fluid was seeded with polyamide particles (ρ=1.1 g/cm3, diameter=100μm), in order to perform flow visualization. Firstly, the hydraulic circuit was characterized in order to obtain physiologic values of flow-rate (within a range of 20-80 ml/min). Then, the coronary artery model under investigation was conveniently illuminated with a continuous LED light and the fields of motion of the fluid were investigated recording videos with a mobile phone. The frames extracted from the videos were analyzed both with PIVlab and OF and some quantities that have shown clinical and predictive interest in the development, formation and progression of atherosclerotic pathologies were obtained, observed and described. The quantities investigated, which allow to obtain relevant information on the fluid dynamics inside the coronary arteries, were calculated with both PIVlab and OF. In this way the results of the two methods were compared with each other, allowing to highlight their potential and defects. Moreover, the experimental velocity values were compared to the characteristic velocities of the vessel, analytically obtained by applying the mass conservation law inside the pipes with variable section, and to the results of CFD fluid dynamics simulations. Taking into account the comparisons made, it is possible to say that both PIVlab and OF allowed to gain good results from a qualitative point of view, and, as a consequence, they can be a valid support in the study of the fluid dynamic structures that are established inside the coronary arteries. In fact, both methods allowed to visualize secondary fluid dynamic structures established in the post-stenotic area of the stenotic vessel. The greatest differences, between the two algorithms were found in terms of computational costs, significantly higher in the OF, and of maximum resolution, which in the PIVlab case is linked to the size of the interrogation windows. Finally, it is possible to assess that the developed test-bench could be potentially used in the clinical and research field, since it is less expensive with respect to the high-cost PIV systems. Moreover, after some implementations, it could also be used for the AIM project, because of the reduced space required to perform the analyses. On the other hand, the quantitative results on the velocity values, for both methods, need further improvements given the presence of non-negligible errors that makes them currently not usable. However, these errors have a large margin of reduction by making some changes and improvements to the instrumentation used for the setup as described in the final part of the work.

Topic: Cardiovascular Health and Disease Prevention
Subfield: Cardiology and Cardiovascular Medicine
Field: Medicine
Domain: Health Sciences