Correlation between angiographic and particle image velocimetry quantifications of flow diverters in an in vitro model of elastase-induced rabbit aneurysms

Abstract

The rupture of a cerebral aneurysm can result in a hemorrhagic stroke. A flow diverter, which is a porous tubular mesh, can be placed across the neck of a cerebral aneurysm to induce the cessation of flow and initiate the formation of an intra-aneurysmal thrombus. By finding a correlation between particle image velocimetry (PIV) and digital subtraction angiography, a better assessment of how well an aneurysm is excluded from the parent artery can be made in the clinical setting. A model of a rabbit elastase-induced aneurysm was connected to a mock circulation loop. The model was then placed under angiography. Recorded angiograms were analyzed so that a contrast concentration-time curve based on the average grayscale intensity inside the aneurysm could be determined. That curve was then fitted to a mathematical model that quantifies the influence of convection and diffusion on contrast transport. Optimized parameters were correlated with the intraneurysmal mean kinetic energy measured by PIV in the same aneurysm model. A strong correlation was observed between the convection and diffusion time constants and the mean kinetic energy inside the aneurysm. Analyzing the flow of angiographic contrast into and out of the aneurysm after implantation of a flow diverter allows for prediction of the efficacy of the device in excluding the aneurysm. Correlating hydrodynamic measures obtained by angiography to those obtained by detailed techniques such as PIV increases confidence in such predictions.

Figure 1

Model-fit to the aneurysmal contrast concentration-time curve (gray line) after implantation of diverter 4 (70% porosity, 21.2 pores/mm² pore density); the dashed line represents the convective process, the dotted line represents the diffusive process and the solid line is the combined process; optimized model parameters are listed; AGI: Average Grayscale Intensity.

Figure 2

Plot of the convective time constant (τ_conv) versus the mean kinetic energy (+). The solid line represents the linear trend and the dashed lines represent the 95% confidence limit

Figure 3

Plot of the diffusive time constant (τ_diff) versus the mean kinetic energy (+). The solid line represents the linear trend and the dashed lines represent the 95% confidence limit