Computational fluid dynamics (CFD) simulations can be leveraged to understand

clinically relevant problems in cardiovascular flows. This talk will describe an 

application of CFD modeling to physiological flows: intracranial flow in the Circle

of Willis (CoW) during vasospasm. The CoW is a redundant network of blood vessels

that perfuses the cerebral tissue. Flow in the collateral pathways that form this ring-

like vascular structure can change in the presence of vessel constriction or occlusion.

After a bleeding event in the subarachnoid space, vessels in the CoW sometimes invol-

untarily constrict, in a phenomenon known as vasospasm, which limits blood flow to

the tissue, potentially causing infarct. The role of collateral pathways in the response

to vasospasm is not well-understood. The relationship

between changes in flow rate and direction in the collateral pathways, the anatomical

variant of the CoW, and localization and severity of vasospasm across the network are all investigated mathematically.

Patient-specific CFD simulations in a cohort of 25 vasospasm patients are conducted,

leveraging computed tomographic angiography (CTA) scans to generate models of

the vasculature and transcranial Doppler ultrasound (TCD) measurements to apply

boundary conditions. Bayesian analysis accounted for parameter uncertainty intro-duced by the medical data and was used to optimize the model parameters applied in the final simulation. Diameters, velocities, and flow rates were benchmarked against

literature values, and virtual angiography performed by tracking a passive scalar, advected by the fluid velocity computed in the CFD simulations, was compared to clinical angiography, showing good agreement. Two metrics for vasospasm severity –

percent changes in resistance and viscous dissipation – correlated closely with angio-

graphic severity and helped identify regions of localization of vasospasm within the

CoW and quantify overall severity.