CONICET | Buscador de Institutos y Recursos Humanos

Purpose: The hemodynamics in intracranial aneurysms treated with coils or flow diverters can be simulated using computational fluid dynamics (CFD) techniques. Commonly, pulsatile boundary conditions are imposed to simulate the transient behavior of blood flow in the circulation. However, less time-consuming steady-state simulations might already provide relevant information on the post-treatment hemodynamics. The purpose of this pilot study was to test the accuracy of steady-state simulations to estimate relevant hemodynamic variables using transient simulations as ground truth. Methods: Anatomical models of one lateral and one terminal aneurysm, both on the ICA, were extracted from 3DRA images. Coils were virtually inserted using a dynamic path planning algorithm. The flow diverter was virtually deployed using a deformable model constrained by stent and vessel geometries. Three configurations were created for the hemodynamic simulations: 1) untreated, 2) treated with coils, and 3) treated with flow diverter (SILK stent). Per configuration, a steady-state and a transient CFD simulation was performed in ANSYS-CFX with a physiologically realistic flow rate waveform (transient) or the corresponding average flow rate of 4.6 mL/s (steady-state) imposed at the inlet. Other parameters included zero-pressure at outlets, rigid wall, and Newtonian blood model. In the data analysis, time-averaged transient results were compared with steady-state results. Focus was put on the treatment-induced flow reduction, which was defined as the difference between the flow into the aneurysm before and after treatment divided by the flow into the aneurysm before treatment.Results: For the terminal aneurysm, the flow reduction was 57.8% (steady-state) and 60.0% (transient) after coiling, while after stenting it was 16.6% (steady-state) and 16.8% (transient). For the lateral aneurysm, the flow reduction was 50.2% (steady-state) and 52.2% (transient) after coiling, while after stenting it was 8.7% (steady-state) and 11.3% (transient). The difference between steady-state and transient simulations in wall shear stress (WSS) on the aneurysm was for all simulations below 5%. Visually, the WSS distributions were categorized as similar. Compared to transient simulations, the CPU time required for steady-state simulations was, on average, 23 times smaller. All, except the untreated lateral aneurysm, solutions converged to obtain a RMS residual of WSS of 10<sup>-5</sup>.Conclusion: For the two studied aneurysms, steady-state hemodynamic simulations were able to accurately estimate the treatment-induced reduction of blood flow into the aneurysm. Future work should study the value of steady-state simulations across more vascular geometries and different flow rate waveforms and should determine the success rate of finding fully converged solutions.

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