Comparative study of flow fluctuations in ruptured and unruptured intracranial aneurysms: A lattice Boltzmann study

Flow fluctuations have recently emerged as a promising hemodynamic metric for understanding the rupture risk of intracranial aneurysms. Several investigations have reported in the literature corresponding flow instabilities using established computational fluid dynamics tools. In this study, the occurrence of flow fluctuations is investigated using either Newtonian or non-Newtonian fluid models in patient-specific intracranial aneurysms using high-resolution lattice Boltzmann method simulations. Flow instabilities are quantified by computing power spectral density, proper orthogonal decomposition and spectral entropy, and fluctuating kinetic energy of velocity fluctuations. Furthermore, these hemodynamic parameters are compared between the ruptured and unruptured aneurysms. Our simulations reveal that the pulsatile inflow through the neck in a ruptured aneurysm is subject to a hydrodynamic instability leading to high-frequency fluctuations around the rupture position throughout the entire cardiac cycle. At other locations, the flow instability is only observed during the deceleration phase; typically, the fluctuations begin there just after peak systole, gradually decay, and the flow returns to its original, laminar pulsatile state during diastole. In the unruptured aneurysm, there is only minimal difference between Newtonian and non-Newtonian results. In the ruptured case, using the non-Newtonian model leads to a considerable increase of the fluctuations within the aneurysm sac.