Abstract
Flow-induced blood damage plays an important role in determining the hemodynamic impact of abnormal blood flow, but quantifying of these effects, which are dominated by shear stresses in highly fluctuating turbulent flow, has not been feasible. This study evaluated the novel application of turbulence tensor measurements using simulated 4D Flow MRI data with six-directional velocity encoding for assessing hemodynamic stresses and corresponding blood damage index (BDI) in stenotic turbulent blood flow. The results showed that 4D Flow MRI underestimates the maximum principal shear stress of laminar viscous stress (PLVS), and overestimates the maximum principal shear stress of Reynolds stress (PRSS) with increasing voxel size. PLVS and PRSS were also overestimated by about 1.2 and 4.6 times at medium signal to noise ratio (SNR) = 20. In contrast, the square sum of the turbulent viscous shear stress (TVSS), which is used for blood damage index (BDI) estimation, was not severely affected by SNR and voxel size. The square sum of TVSS and the BDI at SNR >20 were underestimated by less than 1% and 10%, respectively. In conclusion, this study demonstrated the feasibility of 4D Flow MRI based quantification of TVSS and BDI which are closely linked to blood damage.
Highlights
Flow-induced blood damage plays an important role in determining the hemodynamic impact of abnormal blood flow, but quantifying of these effects, which are dominated by shear stresses in highly fluctuating turbulent flow, has not been feasible
Reference time-averaged velocity fields, turbulent kinetic energy (TKE), and Reynolds stresses were obtained by computational fluid dynamics (CFD) with large eddy simulation (LES) in a 14.6 mm diameter pipe with cosine-shaped stenoses (60, 75 and 90% reduction in area)
A novel application of 4D Flow MRI with ICOSA6 motion-encoding was demonstrated for the assessment of hemodynamic stresses and the corresponding blood damage index (BDI) in turbulent blood flow
Summary
Flow-induced blood damage plays an important role in determining the hemodynamic impact of abnormal blood flow, but quantifying of these effects, which are dominated by shear stresses in highly fluctuating turbulent flow, has not been feasible. This study evaluated the novel application of turbulence tensor measurements using simulated 4D Flow MRI data with six-directional velocity encoding for assessing hemodynamic stresses and corresponding blood damage index (BDI) in stenotic turbulent blood flow. The square sum of the turbulent viscous shear stress (TVSS), which is used for blood damage index (BDI) estimation, was not severely affected by SNR and voxel size. The stresses developed in turbulent flow can be several orders of magnitude larger than the laminar flow[12], and turbulence-induced blood damage is a major concern for prosthetic devices such as mechanical heart valves[13]. Estimation of the Reynolds stress, which is a component of the stress tensor derived using the Reynolds-averaged Navier-Stokes (RANS) technique, has been employed when analyzing turbulent effects on blood constituents in flows through prosthetic valves[14,15,16].
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