Four-Dimensional Flow Magnetic Resonance Imaging for Assessment of Velocity Magnitudes and Flow Patterns in The Human Carotid Artery Bifurcation: Comparison with Computational Fluid Dynamics

Abstract

Purpose: Knowledge of the hemodynamics in the vascular system is important to understand and treat vascular pathology. The present study aimed to evaluate the hemodynamics in the human carotid artery bifurcation measured by four-dimensional (4D) flow magnetic resonance imaging (MRI) as compared to computational fluid dynamics (CFD).

Methods: This protocol used MRI data of 12 healthy volunteers for the 3D vascular models and 4D flow MRI measurements for the boundary conditions in CFD simulation. We compared the velocities measured at the carotid bifurcation and the 3D velocity streamlines of the carotid arteries obtained by these two methods.

Results: There was a good agreement for both maximum and minimum velocity values between the 2 methods for velocity magnitude at the bifurcation plane. However, on the 3D blood flow visualization, secondary flows, and recirculation regions are of poorer quality when visualized through the 4D flow MRI.

Conclusion: 4D flow MRI and CFD show reasonable agreement in demonstrated velocity magnitudes at the carotid artery bifurcation. However, the visualization of blood flow at the recirculation regions and the assessment of secondary flow characteristics should be enhanced for the use of 4D flow MRI in clinical situations.

Keywords: carotid artery; carotid bifurcation; computational fluid dynamics (CFD); flow patterns; four-dimension flow magnetic resonance imaging (4D flow MRI); velocity magnitudes.

Figure 1

Flow chart of the hemodynamic velocity, and the flow pattern comparison process between four-dimensional (4D) flow magnetic resonance imaging (MRI) and computational fluid dynamics (CFD).

Figure 2

Time-varying axial indices of the carotid artery blood flow were analyzed using the 4D flow MRI at 4 slice locations along the vessel axial direction. Data from slices 1, 2, and 3 are used to determine the inflow boundary conditions and the outflow boundary conditions. Slice 4 (bifurcation plane) was used for velocity comparison with CFD results.

Figure 3

(A) Comparison of the velocity waveform at the bifurcation plane derived from 4D flow MRI (red line) and from CFD (dashed line); (B) Bland–Altman plot analysis of velocity data at the carotid bifurcation plane comparing the results of CFD and 4D flow MRI of maximum and minimum velocity. The green lines indicate the mean of the difference between 4D flow MRI and CFD ± 1.96 standard deviation; the red line shows mean difference value.

Figure 4

The flow patterns and velocity fields distribution for 12 carotid arteries at peak systole of 4D flow MRI (left) and CFD (right).

Figure 5

Visualization of velocity streamlines in the carotid artery bifurcation at peak systole using 4D flow MRI and CFD. 4D flow MR images of secondary flow direction and location (arrows) moderately coincide with the CFD visualization. (A) Lateral view; (B) posteroanterior view.

Figure 6

Visualization of velocity streamlines in the carotid artery at peak systole using 4D flow MRI (left) and CFD (right). In the blood flow patterns derived from 4D flow MRI, the velocity streamlines were disconnected at the segment of an arterial wall within the carotid bifurcation domain (black arrow) and recirculation regions were not well captured (red arrow).