Three‐Dimensional Reconstruction of Coronary Arteries

The methods of intracoronary VP have been previously described.16, 17, 18, 19 In brief, IVUS and biplane coronary angiography were utilized to create an accurate three‐dimensional (3D) representation of the coronary artery. IVUS was performed with automated pullback at 0.5 mm/s. The lumen and outer vessel wall were reconstructed from segmented end‐diastolic IVUS frames. Coronary blood flow was calculated directly from the time required for the volume of blood contained within the portion of the artery under study to be displaced by contrast material in coronary angiography.20 The stent was considered only as a zone along the arterial wall and not as a solid‐body geometry. We did not investigate the contours or geometry of individually modeled stents. The 3D geometry of ISH was taken as the difference between the stented region and the lumen area. ESS within the stented region at the luminal surface of the artery was calculated as the product of blood viscosity (calculated from the measured hematocrit) and the gradient of blood velocity at the wall. The process of data acquisition and analysis are highly reproducible.17 In the computational fluid dynamics (CFD) simulations, we impose measured blood flow to pass through the reconstructed geometry under nonslip condition (zero velocity) on the arterial walls. Mathematical model uses linear momentum (the Navier‐Stokes) equations to find the velocity distribution at the faces of computational cells. The CFD model also has shear rates (velocity gradients) in every spatial direction to solve the governing equations. Thus, the gradient of blood velocity at the wall is determined from the shear rate at the computational cell on the wall, as published before.17 More specifically, magnitude of the shear rate is defined based on the strain rate tensor as follows:

Here, i, j=1, 2, 3 are the 3 coordinate directions, and x_i and u_i are, respectively, the dimension and velocity in the direction i. γ˙ above becomes velocity gradient in the normal direction to the wall. In this study, we defined ESS as a measure of flow within the stented portion of the artery and specific stent geometries were not included into our CFD calculations.