3D Quantification of Wall Shear Stress and Oscillatory Shear Index Using a Finite-Element Method in 3D CINE PC-MRI Data of the Thoracic Aorta

Abstract

Several 2D methods have been proposed to estimate WSS and OSI from PC-MRI, neglecting the longitudinal velocity gradients that typically arise in cardiovascular flow, particularly on vessel geometries whose cross section and centerline orientation
strongly vary in the axial direction. Thus, the contribution of longitudinal velocity gradients remains understudied. In this work, we
propose a 3D finite-element method for the quantification of WSS
and OSI from 3D-CINE PC-MRI that accounts for both in-plane
and longitudinal velocity gradients. We demonstrate the convergence
and robustness of the method on cylindrical geometries using
a synthetic phantom based on the Poiseuille flow equation. We also
show that, in the presence of noise, the method is both stable and accurate.
Using computational fluid dynamics simulations, we show
that the proposed 3D method results in more accurate WSS estimates
than those obtained from a 2D analysis not considering
out-of-plane velocity gradients. Further, we conclude that for irregular
geometries the accurate prediction of WSS requires the
consideration of longitudinal gradients in the velocity field. Additionally, we compute 3D maps of WSS and OSI for 3D-CINE
PC-MRI data sets from an aortic phantom and sixteen healthy
volunteers and two patients. The OSI values show a greater dispersión than WSS, which is strongly dependent on the PC-MRI resolution. We envision that the proposed 3D method will improve the
estimation of WSS and OSI from 3D-CINE PC-MRI images, allowing
for more accurate estimates in vessels with pathologies that
induce high longitudinal velocity gradients, such as coarctations
and aneurisms.