Patient-specific cerebral aneurysm hemodynamics: Comparison of in vitro volumetric particle velocimetry, Computational Fluid Dynamics (CFD), and in vivo 4D flow MRI

Typical approaches to patient-specific hemodynamic studies of cerebral aneurysms use image based computational fluid dynamics (CFD) and seek to statistically correlate parameters such as wall shear stress (WSS) and oscillatory shear index (OSI) to risk of growth and rupture. However, such studies have reported contradictory results, emphasizing the need for in-depth comparisons of volumetric experiments and CFD. In this work, we conducted tomographic particle velocimetry experiments using two patient-specific cerebral aneurysm models (basilar tip and internal carotid artery) under pulsatile flow conditions and processed the particle images using Shake the Box (STB), a particle tracking method. The STB data was compared to that obtained from in vivo 4D flow MRI and CFD. Although qualitative agreement of flow pathlines across modalities was observed, each modality maintained notably unique spatiotemporal distributions of low normalized WSS regions. Analysis of time averaged WSS (TAWSS), OSI, and Relative Residence Time (RRT) demonstrated that non-dimensional parameters, such as OSI, may be more robust to the varying assumptions, limitations, and spatial resolutions of each subject and modality. These results suggest a need for further multi-modality analysis as well as development of non-dimensional hemodynamic parameters and correlation of such metrics to aneurysm risk of growth and rupture.