Velocity information is essential for evaluating valvular blood flow. Our protocol acquires instance velocity fields, leading to a detailed analysis of hemodynamics. The main advantage of this protocol is that it can acquire instance velocity fields in the aortic sinus with the prosthetic heart valve implantation, which is hard to obtain from in-vivo experiments.
The current protocol would help characterize the abnormal hemodynamics after transcatheter aortic valve implantation. Based on the obtained hemodynamics, researchers would be able to develop a better heart valve. The process of obtaining good particle images for particle image velocimetry is complicated.
For a beginner, it is recommended to acquire particle images with different frame rates and compare each result. To begin, prepare the experimental setup on an optic table, including a piston pump, data acquisition device, and a computer with the required system engineering software and motor controlling software. Import the spreadsheet file to the system engineering software with the flow rate information.
Fix the acrylic sinus model to the optic table with a square aluminum bar. Connect the reservoir, piston pump, and the acrylic sinus model with a silicone hose. Combine the fixed TAV on the native leaflet with the acrylic sinus model.
Place the high-speed camera on a two-axis traverse and move the traverse. Turn on the laser, set it to seven watts, and place the laser sheet to the center of the TAV. Take a picture and check the maximum particle distance is less than four to six pixels.
Set the camera controlling software parameters starting with a Resolution of 1, 280 by 720, a frame Rate of 300 frames per second, exposure forced by the Burst period, Burst count of three, and Burst period of 200 microseconds and 150 microseconds. Capture particle images for 14 continuous cycles and repeat it a total of seven times. Make the mask by separating the areas to be analyzed from those to be discarded.
Using an open source tool, PIVlab, based on MATLAB, perform PIV by importing particle images saved by the time-resolved method or pair-wise method. Import the mask and apply it to all the particle images. Execute contrast-limited adaptive histogram equalization, execute the cross correlation about the particle image pair converted into the frequency domain using fast Fourier transform.
Set the multi-pass interrogation window, find the peak value using a two-by-three Gaussian fit in correlation result. Calculate the velocity field, derive hemodynamics parameters using the in-house code and built-in function. For the 23-millimeter TAV, the velocity was higher than 0.05 meters per second between TAV and sino-tubular junction from early systole to peak systole.
The velocity at diastole was lower than 0.025 meters per second and two vortexes with low velocity appeared. For 26 millimeter TAV in time except for early systole, velocity distribution in sinus was lower than 0.05 meters per second. Specifically, at late systole, the velocity was lower than at another time.
The peak velocity in 23-millimeter TAV was higher than 26-millimeter TAV. The stasis area formed in 23-millimeter TAV was broad, but the fraction of stasis was low. Two similar vortices were noticed above and below the native leaflet for the 23-millimeter TAV.
However, for the 26-millimeter TAV the clockwise vortex was unclear and the counterclockwise vortex had an elliptical shape. The vorticity showed similar results to the vortex. The snapshots of particle residence showed particle distribution in the sinus region for two seconds, and the percentage of particle residence showed that fraction of remaining particles in the sinus region for 14 seconds.
The 26-millimeter TAV decreased faster than 23-millimeter TAV, however, the release of particles was not identical in both cases. The derivation of velocity fields is the most crucial step. The preceding steps are processes for deriving velocity fields, and are suitable for PIV.
This protocol can be used to investigate hemodynamics in various cardiovascular systems, such as the stenotic arteries and heart valves.
