In Vivo flow and wall shear stress assessment in the carotid artery with MRI

Abstract

Wall shear stress (WSS) exerted by flowing blood at the vessel wall, is defined as the velocity gradient at the vessel wall times the blood viscosity. Low WSS is related to atherosclerotic risk profiles and WSS is low or oscillating at locations where plaque development is observed. In vivo cross-sectional images of blood flow suffer from limited resolution and lack of info on local viscosity. However, WSS can be assessed by modeling of velocity profiles and blood viscosity. Already with a first approximation of velocity profiles by an imprecise model, such as a paraboloid, and under the assumption of a constant (average) human blood viscosity, correlations between various cardiovascular risk factors and WSS were found. Also the effect of treatment with pravastatin on WSS has been demonstrated with this model. The more detailed the model, the more accurate WSS can be assessed. An accurate 4D WSS assessment can be obtained by application of a so-called Finite Element Method (FEM) calculation. Blood velocity was simulated for a certain vessel segment. A model of the vessel geometry composed of bricks (a so called mesh) was created in order to simulate the blood flow.