Post-processing techniques of 4D flow MRI: velocity and wall shear stress

TL;DR

This paper introduces an improved divergence-free smoothing method with near wall treatment for 4D flow MRI data, enhancing the accuracy of velocity and wall shear stress measurements near vessel walls.

Contribution

The study presents a novel DFS method with specific near wall treatment and a wall function for better processing of 4D flow MRI data, especially near vessel walls.

Findings

Enhanced accuracy of velocity field smoothing near vessel walls.

Improved estimation of wall shear stress using the new wall function.

Better handling of noisy and error-prone 4D flow MRI data.

Abstract

As the original velocity field obtained from four-dimensional (4D) flow magnetic resonance imaging (MRI) contains considerable amount of noises and errors, the available Divergence-free smoothing (DFS) method can be used to process the 4D flow MRI data for reducing noises, eliminating errors, fixing missing data and eventually providing the smoothed flow field. However, the traditional DFS does not have the ability to deal with the flow in the near wall region of vessel, especially for satisfying the no-slip boundary condition. In this study, therefore, an improved DFS method with specific near wall treatment is introduced for processing with 4D flow MRI inner flow with curved wall boundary as the blood flows. On the other hand, due to the coarse resolution of 4D flow MRI, velocity gradients in the near wall region are normally underestimated. As a result, a special wall function is required for accurately computing wall shear stress (WSS).