Better Than Nothing: A Rational Approach for Minimizing the Impact of Outflow Strategy on Cerebrovascular Simulations

Area of Science:

• Biomedical Engineering
• Computational Science
• Medical Imaging

Background:

• Computational fluid dynamics (CFD) simulations are crucial for understanding neurovascular diseases like intracranial aneurysms.
• Modeling uncertainties, particularly outlet boundary conditions, significantly impact simulation accuracy.
• Commonly used zero-pressure and diameter-cubed outflow strategies lack physiological basis and introduce subjectivity.

Purpose of the Study:

• To evaluate the limitations of conventional outflow strategies in CFD simulations of neurovascular diseases.
• To introduce and validate a novel "splitting" method for estimating outflow boundary conditions.
• To assess the impact of different outflow strategies on hemodynamic indices relevant to aneurysm rupture status.

Main Methods:

• A novel splitting method was developed, dividing segmented lumens at bifurcations and estimating local flow divisions using a power law.
• The impact of various outflow strategies on flow rates was tested using 0D simulations for 70 MCA aneurysm cases.
• Hemodynamic indices were analyzed using 3D simulations for 10 MCA aneurysm cases to assess rupture status implications.

Main Results:

• Outflow strategies led to flow rate differences of up to 70%.
• The splitting and Murray-law methods yielded flow rates closest to physiological values.
• The splitting method demonstrated robustness against arbitrary model extent truncation, unlike other methods.

Conclusions:

• Cerebrovascular simulation outcomes are highly sensitive to the chosen outflow strategy.
• The default zero-pressure method is physiologically inaccurate and should be replaced by more robust methods.
• The open-source splitting method is recommended for standardization to improve the reliability of neurovascular simulations.