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Session: Image Analysis - Cancer
Session starts: Friday 25 January, 13:00
Presentation starts: 14:00
Room: Lecture room 559

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Merih Cibis ()
Jolanda Wentzel ()
Frank Gijsen ()

Abstract:
Background: Aneurysms are local dilatations of the arterial walls and it is hypothesized that the development of an aneurysm is affected by hemodynamic parameters. CFD is generally used to determine intra-aneurysmal hemodynamics. Cebral [1] studied a patient based aneurysm with a proximal stenosis and applied CFD to predict the effect of stenosis removal. CFD is potentially useful to determine the flow data noninvasively, but is it really reliable? To answer this question, a challenge was organized to compare velocity and pressure in a patient based aneurysm model. Methods: We participated in the challenge in a clinical setting with limited resources and simulation time. We used 4 million tetrahedral elements which was the maximum allowable number of elements in our setting. Two unsteady simulations were performed (low flow and high flow) using realistic inflow waveforms. The steady simulations were at mean and peak flow rates for both unsteady inflows to check the influence of unsteadiness. Linear velocity and pressure basis functions were used which were enabled by using pressure stabilizing Petrov-Galerkin scheme. Segregated pressure based algorithm was chosen with backward Euler time integration. The convergence criterion was set to 1d-3. Results: Low flow rate steady simulations were fully converged. A narrow jet coming from the parent artery impinged to the aneurysm wall. The rest of the aneurysm was filled with low circulating flow. Main pressure drop was at the stenosis proximal to the aneurysm and at the neck of the aneurysm. The pressure drop at flow rate of 6.41 mL/sec was 7.8 mmHg. Steady and unsteady simulations at the same flow rates were in good agreement, so the influence of unsteadiness was found to be small. At high steady flow rates, fully resolved solution could not be achieved. Although the solution was smooth at the parent artery, numerical oscillations were observed at the jet region in the aneurysm sac. The pressure drop at peak flow rate of 11.42 mL/sec was 22.8 mmHg which is in good agreement with Cebral’s paper (25 mmHg). Our results were also consistent with the majority of the CFD groups participated in the challenge. Discussion: Performing simulations of intra-aneurysmal flow was difficult with limited resources due to high velocity gradients in the sac. Fully resolved solutions could not be reached at high flow rates. However, the results in the parent vessel were in good agreement with Cebral and other groups. Although not all details in flow structures in the sac were captured, the results showed that pressure drop computations are feasible with the settings of this study. Therefore, general conclusions were achieved with sufficiently accurate results in our clinical setting. Overall, CFD seems to be able to determine the pressure drop. REFERENCE [1] Cebral et al. Am J Neuroradiol 2011 Jan; 32:27-33