Intra-aneurysmal high-resolution 4D MRI flow imaging for hemodynamic imaging markers in intracranial aneurysm instability

BACKGROUND AND PURPOSE: Prediction of aneurysm instability is crucial to guide treatment decisions and to select appropriate patients with unruptured intracranial aneurysms (IAs) for preventive treatment. High resolution four-dimensional magnetic resonance (4D MRI) flow imaging and 3D quantification of aneurysm morphology could offer insights and new imaging markers for aneurysm instability. In this cross-sectional study, we aim to identify 4D MRI flow imaging markers for aneurysm instability by relating hemodynamics in the aneurysm sac to 3D morphological proxy parameters for aneurysm instability.

MATERIALS AND METHODS: In 35 patients with 37 unruptured IAs, a 3T MRA and a 7T 4D flow MRI scan was performed. Five hemodynamic parameters -peak-systolic (WSS_MAX) and time-averaged wall shear stress (WSS_MEAN), oscillatory shear index (OSI), mean velocity, and velocity pulsatility index (vPI)-were correlated to six 3D morphology proxy parameters of aneurysm instability -major axis length, volume, surface area (all three size parameters), flatness, shape index, and curvedness -by Pearson’s correlation with 95% confidence intervals (CI). Scatterplots of hemodynamic parameters that correlated with IA size (major axis length) were created.

RESULTS: WSS_MAX and WSS_MEAN correlated negatively with all three size parameters (strongest for WSS_MEAN with volume (r = -0.70, 95% CI -0.83 to -0.49)) and OSI positively (strongest with major axis length (r = 0.87, 95% CI 0.76 to 0.93)). WSS_MAX and WSS_MEAN correlated positively with shape index (r = 0.61, 95% CI 0.36 to 0.78 and r = 0.49, 95% CI 0.20 to 0.70, respectively) and OSI negatively (r = 0.82, 95% CI -0.9 to -0.68). WSS_MEAN and mean velocity correlated negatively with flatness (r = -0.35, 95% CI -0.61 to -0.029 and r = 0.33, 95% CI -0.59 to 0.007, respectively) and OSI positively (r = 0.54, 95% CI 0.26 to 0.74). vPI did not show any statistically significant correlation.

CONCLUSIONS: Out of the five included hemodynamic parameters, WSS_MAX, WSS_MEAN, and OSI showed the strongest correlation with morphological 3D proxy parameters of aneurysm instability. Future studies should assess these promising new imaging marker parameters for predicting aneurysm instability in longitudinal cohorts of IA patients.

ABBREVIATIONS: IA = intracranial aneurysm; 3D = three dimensional; 4D MRI flow = four-dimensional Magnetic Resonance Imaging flow; TOF-MRA = Time-of-flight Magnetic Resonance Angiography; WSS = wall shear stress; WSS_MAX = WSS calculated at peak systole; WSS_MEAN = time averaged WSS; OSI = oscillatory shear index; vPI = velocity pulsatility index