Numerical modelling of a vascular palpation device for assessing intracranial aneurysm wall mechanics under heterogeneous conditions.

Background

The mechanical properties of the intracranial aneurysm wall are not taken into account in current rupture risk scores. A deformation device prototype was previously developed to characterize aneurysm wall mechanics in vivo through controlled deformation and inverse analysis. Its ability to detect localized mechanical heterogeneities within the aneurysm wall has not been assessed.

Methods

A finite element fluid-structure interaction model of a representative cerebral artery with a saccular aneurysm was developed. Seven mechanical models were considered: homogeneous walls, globally weakened aneurysm sacs, and models including localized weakened areas of 1 to 2.2 mm2 with rupture-associated parameters. Four device locations and two flow rates were studied under physiological blood flow conditions. Wall displacements, luminal volume variation, inner wall pressure and maximal principal strain were compared between configurations with and without the device.

Findings

Wall displacements induced by the device ranged from 372 to 733μm at systole peak, remaining within physiological bounds. Luminal volume variation did not allow the distinction between weakened areas and homogeneous walls. In contrast, the maximal principal strain variation showed an enlargement of ranges in weakened areas, and these ranges became distinguishable from homogeneous walls when the device was applied at systole against diastole without it.

Interpretation

Within the modelling framework considered, inner wall displacements and luminal volume variation alone were inadequate to identify localized weakened zones, whereas the maximal principal strain appeared to be a pertinent quantity to detect and characterize such mechanical heterogeneities.