Transitional hemodynamics in intracranial aneurysms - Comparative velocity investigations with high resolution lattice Boltzmann simulations, normal resolution ANSYS simulations, and MR imaging.
OBJECTIVE
Blood flow in intracranial aneurysms has, until recently, been considered to be disturbed but still laminar. Recent high resolution computational studies have demonstrated, in some situations, however, that the flow may exhibit high frequency fluctuations that resemble weakly turbulent or transitional flow. Due to numerous assumptions required for simplification in computational fluid dynamics (CFD) studies, the occurrence of these events, in vivo, remains unsettled. The detection of these fluctuations in aneurysmal blood flow, i.e., hemodynamics by CFD, poses additional challenges as such phenomena cannot be captured in clinical data acquisition with magnetic resonance (MR) due to inadequate temporal and spatial resolutions. The authors' purpose was to address this issue by comparing results from highly resolved simulations, conventional resolution laminar simulations, and MR measurements, identify the differences, and identify their causes.


METHODS
Two aneurysms in the basilar artery, one with disturbed yet laminar flow and the other with transitional flow, were chosen. One set of highly resolved direct numerical simulations using the lattice Boltzmann method (LBM) and another with adequate resolutions under laminar flow assumption were conducted using a commercially available ANSYS Fluent solver. The velocity fields obtained from simulation results were qualitatively and statistically compared against each other and with MR acquisition.


RESULTS
Results from LBM, ANSYS Fluent, and MR agree well qualitatively and quantitatively for one of the aneurysms with laminar flow in which fluctuations were <80 Hz. The comparisons for the second aneurysm with high fluctuations of > ∼ 600 Hz showed vivid differences between LBM, ANSYS Fluent, and magnetic resonance imaging. After ensemble averaging and down-sampling to coarser space and time scales, these differences became minimal.


CONCLUSIONS
A combination of MR derived data and CFD can be helpful in estimating the hemodynamic environment of intracranial aneurysms. Adequately resolved CFD would suffice gross assessment of hemodynamics, potentially in a clinical setting, and highly resolved CFD could be helpful in a detailed and retrospective understanding of the physiological mechanisms.
Simulation Techniques and Scientific Computing, University of Siegen, Hölderlinstr. 3, 57076 Siegen, Germany and Center for Biomedical Computing, Simula Research Laboratory, N-1325 Lysaker, Norway.
Kartik
K
Jain
Department of Biomedical Engineering, Michigan Technological University, Houghton, Michigan 49931.
Jingfeng
J
Jiang
University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin 53705.
Charles
C
Strother
Department of Mathematics, University of Oslo, 0316 Oslo, Norway and Center for Biomedical Computing, Simula Research Laboratory, N-1325 Lysaker, Norway.
Kent-André
KA
Mardal
D006439:Hemodynamics; D006801:Humans; D002532:Intracranial Aneurysm / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D008279:Magnetic Resonance Imaging; D008954:Models, Biological; D012189:Retrospective Studies