Reconciling PC‐MRI and CFD: An in‐vitro study

Abstract

Several well-resolved 4D Flow MRI acquisitions of an idealized rigid flow phantom featuring an aneurysm, a curved channel as well as a bifurcation were performed under pulsatile regime. The resulting hemodynamics were processed to remove MRI artifacts. Subsequently, they were compared with CFD predictions computed on the same flow domain, using an in-house high-order low dissipative flow solver. Results show that reaching a good agreement is not straightforward but requires proper treatments of both techniques. Several sources of discrepancies are highlighted and their impact on the final correlation evaluated. While a very poor correlation (r 2 = 0.63) is found in the entire domain between raw MRI and CFD data, correlation as high as r 2 = 0.97 is found when artifacts are removed by post-processing the MR data and down sampling the CFD results to match the MRI spatial and temporal resolutions.This work demonstrates that, in a well-controlled environment, both PC-MRI and CFD might bring reliable and correlated flow quantities when a proper methodology to reduce the errors is followed. KEYWORDS cardiovascular blood flows, computational fluid dynamics, large eddy simulation, phase contrast magnetic resonance imaging, validation work flow

Evaluation and verification of patient-specific modelling of type B aortic dissection

“…However, the dominant direction of flow (ux or uy depending on the geometry orientation) mostly still saw reasonable correlations greater than 0.5, while the non-dominant components (mainly uz) had the lowest R values. Generally the R values found in this study are in line with values reported in previous studies: R = 0.64-0.92 in a healthy patient [36]; R=0.63 in an idealised aortic aneurysm geometry [37]; and R=0.74-0.87 in an ascending aorta aneurysm patient [35].…”

Evaluation and verification of patient-specific modelling of type B aortic dissection

“…However, the dominant direction of flow (ux or uy depending on the geometry orientation) mostly still saw reasonable correlations greater than 0.5, while the non-dominant components (mainly uz) had the lowest R values. Generally the R values found in this study are in line with values reported in previous studies: R = 0.64-0.92 in a healthy patient [36]; R=0.63 in an idealised aortic aneurysm geometry [37]; and R=0.74-0.87 in an ascending aorta aneurysm patient [35].…”

Towards multi‐modal data fusion for super‐resolution and denoising of 4D‐Flow MRI

“…This indicates that the pure CFD simulation cannot be corrected just by scaling the velocity values by a constant factor. It can also be seen that the simulated 4D‐Flow MRI has lower velocity magnitudes compared to the reference CFD simulation, which is a result of the limited spatial‐resolution and volume averaging; similar results have been reported by other researchers 36,68,69 . The patient specific pure CFD simulation which relies on boundary conditions estimated from the simulated 4D‐Flow MRI has lower velocity magnitudes compared to the simulated 4D‐Flow MRI.…”

Assessment of turbulent blood flow and wall shear stress in aortic coarctation using image-based simulations

“…It can be seen that the reduction of spatial resolution of CFD reduced the peak values, but also introduced a shift of the peak location. Similar behavior was shown also in a related study of [ 22 ], but these findings were not addressed. This shift should be taken into account when analyzing cases where the exact location of the peak WSS is of importance.…”

Evaluation and verification of patient-specific modelling of type B aortic dissection

“…However, the dominant direction of flow (ux or uy depending on the geometry orientation) mostly still saw reasonable correlations greater than 0.5, while the non-dominant components (mainly uz) had the lowest R values. Generally the R values found in this study are in line with values reported in previous studies: R = 0.64-0.92 in a healthy patient [36]; R=0.63 in an idealised aortic aneurysm geometry [37]; and R=0.74-0.87 in an ascending aorta aneurysm patient [35].…”

Towards multi‐modal data fusion for super‐resolution and denoising of 4D‐Flow MRI

“…This indicates that the pure CFD simulation cannot be corrected just by scaling the velocity values by a constant factor. It can also be seen that the simulated 4D‐Flow MRI has lower velocity magnitudes compared to the reference CFD simulation, which is a result of the limited spatial‐resolution and volume averaging; similar results have been reported by other researchers 36,68,69 . The patient specific pure CFD simulation which relies on boundary conditions estimated from the simulated 4D‐Flow MRI has lower velocity magnitudes compared to the simulated 4D‐Flow MRI.…”

Assessment of turbulent blood flow and wall shear stress in aortic coarctation using image-based simulations

“…It can be seen that the reduction of spatial resolution of CFD reduced the peak values, but also introduced a shift of the peak location. Similar behavior was shown also in a related study of [ 22 ], but these findings were not addressed. This shift should be taken into account when analyzing cases where the exact location of the peak WSS is of importance.…”

Evaluation and verification of patient-specific modelling of type B aortic dissection

“…However, the dominant direction of flow (ux or uy depending on the geometry orientation) mostly still saw reasonable correlations greater than 0.5, while the non-dominant components (mainly uz) had the lowest R values. Generally the R values found in this study are in line with values reported in previous studies: R = 0.64-0.92 in a healthy patient [36]; R=0.63 in an idealised aortic aneurysm geometry [37]; and R=0.74-0.87 in an ascending aorta aneurysm patient [35].…”

Towards multi‐modal data fusion for super‐resolution and denoising of 4D‐Flow MRI

“…This indicates that the pure CFD simulation cannot be corrected just by scaling the velocity values by a constant factor. It can also be seen that the simulated 4D‐Flow MRI has lower velocity magnitudes compared to the reference CFD simulation, which is a result of the limited spatial‐resolution and volume averaging; similar results have been reported by other researchers 36,68,69 . The patient specific pure CFD simulation which relies on boundary conditions estimated from the simulated 4D‐Flow MRI has lower velocity magnitudes compared to the simulated 4D‐Flow MRI.…”

Assessment of turbulent blood flow and wall shear stress in aortic coarctation using image-based simulations

“…It can be seen that the reduction of spatial resolution of CFD reduced the peak values, but also introduced a shift of the peak location. Similar behavior was shown also in a related study of [ 22 ], but these findings were not addressed. This shift should be taken into account when analyzing cases where the exact location of the peak WSS is of importance.…”