Intracranial Aneurysm Wall Displacement Predicts Instability

Ruptured intracranial aneurysms (IAs) are catastrophic events associated with a high mortality rate. An estimation of 6 million people in the United States have reported IAs, raising a pressing need for diagnostic tools to assess IAs rupture risks. Current population-based guidelines are imperfect, hence the need for new quantifiable variables and imaging markers. Aneurysm wall motion has been identified as a potential marker of high risk aneurysms, but conventional imaging techniques are challenged by small IAs sizes and limited spatial resolution. Recently, amplified Flow (aFlow) has been introduced as an algorithm which allows visualization and quantification of aneurysm wall motion based on amplification of 4D flow MRI data. In this work, we used aFlow to assess IAs wall motion in patients with growing aneurysms. The results were compared with a patient cohort with stable aneurysms. Among 118 patients with unruptured IAs who underwent sequential surveillance imaging, 10 patients with growing IAs who had baseline 3D TOF-MRA and 4D flow MR imaging were identified and matched with another cohort of patients with stable IAs based on IAs size and location. aFlow was then applied to the 4D flow MR data to amplify the aneurysm wall displacement. Voxel-based values of displacement were extracted for each aneurysm and normalized with respect to the reference parent artery. Following histogram analysis, the highest and lowest IAs displacements were calculated, together with their standard deviation and interquartile ranges. A paired-wise analysis was adopted to assess the differences among clinical variables, demographic data, morphological features, and aFlow parameters between patients with stable versus growing aneurysm. Results demonstrated higher wall motion and higher variability of deformation for the growing aneurysms, possibly due to inhomogeneities of the mechanical characteristics of the vessels walls or to underlying hemodynamics. Computational Fluid Dynamic simulation was also conducted for a subset of 6 stable and 6 growing aneurysms to examine the correlation between hemodynamic parameters, wall motion, and aneurysm stability. The magnitude and variance of directional wall shear stress gradient, in addition to area of colocation of elevated oscillatory shear stress and high variance in pressure, were highly correlated with both wall motion and aneurysm stability. We demonstrated here that the measurement and amplification of the aneurysm wall motion achieved with our method has the potential to differentiate stable from growing aneurysms, and potentially act as a substitute for in depth computational fluid dynamic analysis.