Berkeley Fluids Seminar
University of California, Berkeley
Bring your lunch and enjoy learning about fluids!
November 6, 2013
Dr. Vitaliy L. Rayz (Radiology and Biomedical Imaging, UC San Francisco)
Numerical modeling of blood flow resulting from surgical procedures in brain aneurysms
Cerebral aneurysms are localized dilatations of arteries feeding the brain. Large cerebral aneurysms present a danger of rupture or brain compression. In some cases, in order to treat a complex aneurysm which cannot be completely removed, clinicians consider flow altering procedures in the hope that decreasing the flow through the aneurysm would inhibit its progression. This can be achieved either by clipping some of the upstream or downstream arteries or by redirecting the flow with a stent-like flow diverting device. Our research objective is to develop a patient-specific CFD methodology that could provide guidance to clinicians by modeling postoperative flow fields resulting from alternative surgical procedures.
In order to construct patient-specific models of the aneurysms we use magnetic resonance images (MRI) of the blood vessels obtained prior to a surgery. In addition, MRI velocity measurements are used to acquire patient-specific boundary conditions for the upstream and downstream arteries. The preoperative models are then modified to include changes that would result from the proposed procedures. Numerical solution of the Navier-Stokes equations is obtained with an iterative, finite-volume solver FLUENT. In addition, the advection-diffusion equation is solved in order to simulate contrast agent transport and results are used to estimate the flow residence time (RT). Intra-aneurysmal regions characterized by reduced velocities and shear stresses as well as increased RT are likely to clot following the procedure.
In some cases the flow fields resulting from alternative surgical options are dramatically different. For example, Figure 1 is showing the CFD-predicted transport of a virtual contrast agent in a large aneurysm for two treatment scenarios: clipping of one or the other supplying artery. The contrast flow animation shows that clipping the left feeding vessel (a) would result in a strong jet entering the aneurysm. If the right feeding vessel is clipped (b), the contrast quickly flows into the downstream artery, while the flow residence time in the aneurysm is increased. The later scenario is likely to promote aneurysm clotting.
Another patient's aneurysm was proposed for treatment by a flow diverter device. Numerical simulations of the preoperative and postoperative flow fields are shown in Figure 2 (a) and (b). The simulations predicted that deploying a flow diverter would eliminate a high velocity jet and lead to substantially reduced velocities in the aneurysm. These computational results were validated by experimental measurements conducted in a patient-specific flow phantom where an actual flow diverter device was deployed (Fig. 2c).
The results indicate that CFD models constructed from medical imaging data can be used to predict postoperative flow in cerebral aneurysms. This information, available prior to surgery, may help improve the outcome of surgical procedures.
Figure 1: CFD-predicted virtual contrast transport resulting from clipping of the left (a) or right (b) feeding artery.
Figure 2: (a) Preoperative streamlines computed with CFD: streamlines following flow diverter placement predicted with CFD (b) and obtained with experimental measurements.