Accuracy of Computational Cerebral Aneurysm Hemodynamics Using Patient-Specific Endovascular Measurements

Abstract

Computational hemodynamic simulations of cerebral aneurysms have traditionally relied on stereotypical boundary conditions (such as blood flow velocity and blood pressure) derived from published values as patient-specific measurements are unavailable or difficult to collect. However, controversy persists over the necessity of incorporating such patient specific conditions into computational analyses. We perform simulations using both endovascular-derived patient-specific and typical literature-derived inflow and outflow boundary conditions. Detailed three-dimensional anatomical models of the cerebral vasculature are developed from rotational angiography data, and blood flow velocity and pressure are measured in situ by a dual-sensor pressure and velocity endovascular guidewire at multiple peri-aneurysmal locations in ten unruptured cerebral aneurysms. These measurements are used to define inflow and outflow boundary conditions for computational hemodynamic models of the aneurysms. The additional in situ measurements which are not prescribed in the simulation are then used to assess the accuracy of the simulated flow velocity and pressure drop. Simulated velocities using patient-specific boundary conditions show good agreement with the guidewire measurements at measurement locations inside the domain, with no bias in the agreement and a random scatter of ≈25%. Simulated velocities using the simplified, literature-derived values show a systematic bias and over-predicted velocity by ≈30% with a random scatter of ≈40%. Computational hemodynamics using endovascularly measured patient-specific boundary conditions have the potential to improve treatment predictions as they provide more accurate and precise results of the aneurysmal hemodynamics than those based on commonly accepted reference values for boundary conditions.

Hemodynamics in growing and stable cerebral aneurysms

“…Growing and stable unruptured aneurysms were selected from a database of untreated patients when longitudinal imaging studies were available. Finally, computational fluid dynamics models make several assumptions such as rigid walls, Newtonian flows, normal physiologic conditions, etc (for a new approach to boundary conditions see McGah et al 30). Despite these limitations, interesting observations could be made—namely, that growing and stable aneurysms share some associations with ruptured and unruptured aneurysms but also present interesting differences that should be taken into consideration when investigating the mechanisms responsible for aneurysm progression and rupture.…”

Unraveling the relationship between arterial flow and intra-aneurysmal hemodynamics

“…Currently, a single-flow condition is used to assess WSS. Nevertheless, arterial flow rate changes at short and long terms, thus affecting aneurysmal quantities, like WSS or velocity (Jiang and Strother, 2009;Marzo et al, 2011;McGah et al, 2014). Therefore, there is not a unique WSS (nor for any hemodynamic variable) for a given patient but a physiological range of WSS, which depends on the range of the arterial flow rates of the patient (Fig.…”

“…Inside aneurysms, flow patterns and quantitative variables, such as velocity and wall shear stress (WSS), vary if flow conditions change (Jiang and Strother, 2009;Marzo et al, 2011;McGah et al, 2014). Moreover, CFD-based studies have highlighted the importance of imposing patient-specific flow rates and have quantified the errors when derived boundary conditions are used (Marzo et al, 2011;McGah et al, 2014). Nevertheless, patientspecific measurements are limited to the temporal frame of the examination.…”

Predictive modeling and in vivo assessment of cerebral blood flow in the management of complex cerebral aneurysms

“…Optimizing the predictive power of these models requires further study with endovascular quantitative flow assessment techniques and postoperative time-resolved angiography to provide further refinements and validation. 27 As CFD workflow routines become more streamlined and efficient, it is likely that other aneurysms, in addition to those not requiring bypass techniques, may also benefit from preoperative evaluation. Examples of this include preoperative models to reconstruct parent vessels with aneurysm clips prior to microsurgical clip occlusion and to determine flow alterations in branch arteries that originate from the aneurysm necks prior to flow diversion.…”