CFD SIMULATION OF BLOOD FLOW BEHIND ...

CFD SIMULATION OF BLOOD FLOW BEHIND ENDOVASCULAR DEVICES Georg Mach(a, b), Ursula Windberger(a, c), Roberto Plasenzotti(a, b, c), Camillo Sherif(a, b, d) (a) Cerebrovascular Research Group Vienna, Vienna, Austria (b) CVTec Cerebrovascular Technologies GmbH, Vienna, Austria (c) Department of Biomedical Research, Medical University of Vienna, Vienna, Austria (d) Faculty of Medicine, Sigmund Freud University, Vienna, Austria When calculating the blood flow in cerebral arteries and intracranial aneurysms with CFD simulations, blood is usually modeled as a Newtonian fluid, neglecting its shear-thinning behavior. This simplification is generally permissible due to high shear rates [1]. Treatment with endovascular devices leads to much slower and more constant flows inside the aneurysm sack, thus the accuracy of the Newtonian model has to be reviewed. We measured the viscosity of whole blood samples at a constant temperature and various shear rates using a double gap cylinder viscosimeter. The results were then used to determine the factors of a Carreau Yasuda model [2] utilizing weighted non linear least square regression (see Fig.1). Using Comsol Multiphysics to model a stented side wall aneurysm at a bend cerebral artery we then calculated the velocity of the blood stream comparing both viscosity models (see Fig. 2).

Figure 1: Viscosity models of blood

Figure 2: Error of the Newtonian velocity profile

Against the first intuition and in contrary to other literature [3], the Newtonian model overestimates the effect of the flow diverting stent. Using the Carreau Yasuda model the average velocity within the aneurysm sack is 13.7% higher. To further improve the model, different in vivo examples should be calculated and the calculations should be verified utilizing eg. particle image velocimetry. [1] Cebral JR et al., Efficient Pipeline for Image-Based Patient-Specific Analysis of Cerebral Aneurysm Hemodynamics: Technique and Sensitivity, IEEE Trans Med Imag 2005; 24(4):457-67. [2] Boyd J et al., Analysis of the Casson and Carreau-Yasuda Non-Newtonian Blood Models in Steady and Oscillatory Flows Using the Lattice Boltzmann Method, Physics of Fluids 2007; 19(9). [3] Morales HG et al., Newtonian and Non-Newtonian Blood Flow in Coiled Cerebral Aneurysms, J Biomech 2013; 46(13):2158–64.