Assessment of turbulent viscous stress using ICOSA 4D Flow MRI for prediction of hemodynamic blood damage

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.

Validation of pressure drop assessment using 4D flow MRI‐based turbulence production in various shapes of aortic stenoses

“…4D flow MRI measurements were performed using a clinical 1.5T MRI scanner (Philips Achieva; Philips Medical Systems, Best, the Netherlands). A conventional gradient‐echo sequence with asymmetric 4‐point flow encoding was modified to have a six‐directional icosahedral flow encoding (ICOSA6) and one flow‐compensated reference encoding . To maintain the same experimental conditions for all flow rate and valves conditions, the following four different velocity encoding parameter (VENC) were repetitively used: 1, 2, 3, and 5 m/s.…”

“…A conventional gradient-echo sequence with asymmetric 4-point flow encoding was modified to have a six-directional icosahedral flow encoding (ICOSA6) and one flow-compensated reference encoding. 11,17,24 To maintain the same experimental conditions for all flow rate and valves conditions, the following four different velocity encoding parameter (VENC) were repetitively used: 1, 2, 3, and 5 m/s. TE and TR were 1.5-2.2 ms and 3.2-3.9 ms, respectively.…”

“…Estimation of three velocity components and six Reynolds stresses from 4D flow MRI with ICOSA6 encoding was processed as described in previous publications. 11,24 Data obtained with VENC = 5 m/s were used to extract the velocity of the flow. The velocity field obtained without flow was used to correct the velocity offsets caused by background phase errors.…”

“…This leads to an overestimation of the l 2 norm of the strain rate. 24 In addition, estimation of strain rate fields using 4D flow MRI can also be influenced by the spatial resolution of 4D flow MRI, which is typically ~2-3 mm. 36 Therefore, unless the effects of measurement noise and spatial resolution on the shear-scaling method are clearly identified, the pressure drop prediction of the shear-scaling method cannot be directly interchangeable with other pressure estimations but would be a relative metric.…”

4D Flow MRI quantification of blood flow patterns, turbulence and pressure drop in normal and stenotic prosthetic heart valves

“…4D Flow MRI not only provides a three-dimensional velocity field of the blood flow, but also reveals the extent and degree of turbulence downstream of the PHV, which is suggestive of abnormalities in the blood flow [9]. Assessment of the turbulence level of the blood flow using 4D Flow has been proposed to evaluate flow-induced blood damage to blood constituencies and also the pressure drop observed in stenotic blood flow [13,14].…”