Cerebral Aneurysm Hemodynamic Comparison between Computational Fluid Dynamics and Dual-venc 4D Flow MRI

Hemodynamic forces affecting cerebral aneurysm progression can be assessed with CFD or, alternatively, with time-resolved, 3-directional phase-contrast MRI (4D flow MRI). 4D flow dynamic range is determined by the velocity encoding parameter (venc), set above the expected maximum velocity, which can result in low velocity-to-noise ratio (VNR) for slow flow. A novel, dual-venc 4D flow MRI technique, combining high- and low-venc acquisitions, can improve VNR and, therefore, quantification of flow metric. In this study, superior resolution of CFD was used to assess the advantages of dual-venc relative to a single-venc 4D flow acquisition. 4D flow MRI and MRA data acquired for 5 cerebral aneurysms at Northwestern University were used to generate vascular geometries and prescribe inlet-outlet waveforms. The Navier-Stokes equations were solved with the finite-volume solver ANSYS Fluent. Preliminary results show that dual-venc technique improves velocimetry in flow separation regions; however, the resolution in small intracranial vessels impedes accurate estimation of near-wall velocity gradients. The average difference between the dual-venc and CFD velocities was 2.5% smaller than that for single-venc. Further quantification of the differences between CFD and 4D flow will be presented.