Time-resolved Particle Image Velocimetry measurements for the in vitro characterization of the local fluid dynamics in stented coronary artery phantoms

Coronary arteries play a crucial role in blood circulation by providing a continuous supply of oxygen and nutrients to the heart. Due to systemic factors and the presence of local haemodynamic factors, coronary arteries can be prone atherosclerotic plaque formation, which can lead to vessel obstruction. The implantation of an intravascular stent at the narrowed coronary artery is one of the main procedures used in the presence of advanced atherosclerosis. Notwithstanding its advantages, the presence of a non-biological device causes an inflammatory response within the artery. Indeed, the stent leads to a geometric change within the vessel, acting as a barrier to flow and influencing the fluid dynamic behaviour in regions close to the arterial wall, potentially leading to adverse events, such as in-stent restenosis or thrombosis. In this context, the aim of this thesis work is the in vitro characterization of the local fluid dynamics of a stented coronary artery through particle imaging velocimetry (PIV). To achieve a higher spatial resolution of the measurement, fluid dynamic similarity was used. Starting from the ranges of the physiological dimensionless Reynolds and Womersley numbers and keeping them constant, the larger scaled diameter to be used in the experiments was obtained. Specifically, a 11 mm transparent plexiglass tube was used in which a 3D-printed coronary stent with an outer diameter of 10.8 mm was implanted, obtained from the corresponding original CAD model of 3.5 mm by applying a scaling factor of 3.08. The measurements included an initial experimental campaign with a low-cost PIV system (referred as SMART PIV) comprising a continuous wave laser and a mobile phone camera with a frame rate of 60 Hz. The latter configuration allowed time-resolved acquisitions to study the dynamics of the pulsed flow, simulated with a volume pump providing a periodic flow rate with a physiological waveform proper to the circumflex left coronary artery. A second experimental campaign was carried out with a standard PIV system, with a high-resolution camera and a double pulsed laser with an acquisition frequency of 10 Hz. Time-resolved measurements were also carried out in the latter case. A comparison in terms of technique and resolution between the results obtained with the standard PIV system and those obtained with the SMART PIV system was conducted. While the images obtained with the SMART PIV presented a velocity vector spacing of 292 µm, those obtained with the standard PIV system had a slightly higher resolution (243 µm between every vector). The results of SMART PIV system showed the dynamic changes of the velocity profile during the cardiac period within the stent. SMART PIV can also detect and quantify the intrusiveness of implanted stent in terms of WSS with values that agree with previous experimental studies. Measurements with the standard PIV system also allowed the WSS to be calculated and the results were of the same order of magnitude as those found in the SMART PIV system. Finally, the estimation of the relative error made on both systems showed that the SMART system introduced a lower uncertainty in the PIV measurements.