MRI measurement of time-resolved wall shear stress vectors in a carotid bifurcation model, and comparison with CFD predictions.

Abstract

To study pulsatile fluid flow in a physiologically realistic model of the human carotid bifurcation, and to derive wall shear stress (WSS) vectors. WSS vectors were calculated from time-resolved 3D phase-contrast (PC) MRI measurements of the velocity field. The technique was first validated with sinusoidal flow in a straight tube, and then used in a model of a healthy human carotid bifurcation. Velocity measurements in the inflow and outflow regions were also used as boundary conditions for computational fluid dynamics (CFD) calculations of WSS, which were compared with those derived from MRI alone. The straight tube measurements gave WSS results that were within 15% of the theoretical value. WSS results for the phantom showed the main features expected from fluid dynamics, notably the low values in the bulb region of the internal carotid artery, with a return to ordered flow further downstream. MRI was not able to detect the high WSS values along the divider wall that were predicted by the CFD model. Otherwise, there was good general agreement between MRI and CFD. This is the first report of time-resolved WSS vectors estimated from 3D-MRI data. The technique worked well except in regions of disturbed flow, where the combination with CFD modeling is clearly advantageous.