Flow structures in cerebral aneurysms

Abstract

General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Full terms of use are available: http://www.bristol.ac.uk/pure/about/ebr-terms AbstractMechanical properties of blood flow are commonly correlated to a wide range of cardiovascular diseases. In this work means to describe and characterise the flow field in the free-slip and no-slip domains are discussed in the context of cerebral aneurysms, reconstructed from in-vivo medical imaging. The approaches rely on a Taylor series expansion of the velocity field to first order terms that leads to a system of ODEs, the solution to which locally describes the motion of the flow. On performing the expansion on the vessel wall using the wall shear stress, the critical points can be identified and the near-wall flow field parallel to the wall can be concisely described and visualised. Furthermore the near-wall expansion can be expressed in terms of relative motion, and the near-wall convective transport normal and parallel to the wall can be accurately derived on the no-slip domain. Together, these approaches give a viable and robust means to identify and describe fluid mechanic phenomena both qualitatively and quantitatively, leading to feasible practical use in biomedical applications. From analysis of steady and unsteady flow simulations in two anatomically accurate cerebral saccular aneurysm cases, a set of measures can be readily obtained at all time intervals, including the impingement region, separation lines, convective transport near the wall and vortex core lines or structures, which have all been related to diseased states. Other fluid mechanic measures are also discussed in order to give further detail and insight during postprocessing, and may play an important role in the growth and rupture of the aneurysm.

Quantifying the Large-Scale Hemodynamics of Intracranial Aneurysms

“…21,22 However, the frequent need for a user supplied threshold to construct these surfaces led us to use line-type methods for visualizing and analyzing the spatial structure of hemodynamic flows. 23–26 Irregular aneurysm geometries make the task of identifying a “characteristic length” difficult and subjective. As a result, we used the unnormalized length.…”

Wall shear stress exposure time: a Lagrangian measure of near-wall stagnation and concentration in cardiovascular flows

“…The fixed points that are of saddle-type (i.e their two eigenvalues are real and have different signs, and the eigenvectors are real) are identified. These fixed points are perturbed along the positive eigenvector (i.e., corresponding to the positive eigenvalue) in two opposite directions to obtain two initial conditions [22]. The WSS trajectories constructed from these initial conditions in forward time will trace out the unstable manifold.…”

“…The time step was chosen to divide the cardiac cycle (T = 0.88 s) into 5000 time steps. A cerebral aneurysm model used in a previous study [22] was remeshed with a higher mesh resolution (next to wall edge size of 100 µm). The same boundary conditions and parameters used in [22] were specified.…”

“…A cerebral aneurysm model used in a previous study [22] was remeshed with a higher mesh resolution (next to wall edge size of 100 µm). The same boundary conditions and parameters used in [22] were specified. A typical volumetric waveform was used at the inlet with the flow rate scaled according to the inlet cross section area.…”

Identification of vortex structures in a cohort of 204 intracranial aneurysms

“…Additional studies based on large patient cohorts have found that vortex core lines in ruptured aneurysms exhibit more temporal and spatial fluctuations [18,19]. Because vortex core lines only show the skeleton of the entire vortex structure, and identification of twodimensional planes can be subjective, the true association of vortical flow and IA rupture status remains unclear.…”