Cerebral Aneurysm Wall Diameter Measurements Using High Field MR-Imaging

Background: Thin cerebral aneurysm wall diameter (AWD) is connected to high aneurysm rupture risk. MR imaging of AWD leads to MR overestimations. The present study aimed to quantify this inaccuracy of MR imaging by comparison with "real" AWD light microscopic measurements. Materials and Methods: In 13 experimental microsurgical bifurcation aneurysms in rabbits, 3Tesla (3T)-MR imaging using contrast enhanced T1 Flash sequences (resolution: 0.4x0.4x1.5mm(3)) was performed. Directly after MR acquisition the aneurysms were retrieved, longitudinally cutted and calibrated photographs were obtained. AWD (dome, neck) and parent vessel diameter (PVD) were measured on the MR-images and microscopic photographs by independent investigators. All parameters were statistically compared (Wilcoxon test, Spearman correlation). Results: AWD and PVD could be imaged and measured in all aneurysms with good quality. Comparison with the "real" light microscopic measurements showed a progressive tendency of MR AWD overestimation with smaller AWD: AWD at the dome (0.24 +/- 0.06mm vs. MR 0.30 +/- 0.08mm; p=0.0078; R=0.6125), AWD at the neck (0.25 +/- 0.07mm vs. MR 0.29 +/- 0.07mm; p=0.0469; R=0.7451), and PVD (0.46 +/- 0.06mm vs. MR 0.48 +/- 0.06mm; p=0.5; R=0.8568). Conclusion: In an experimental setting 3T-MR imaging of cerebral AWD showed considerable inaccuracies below the image resolution threshold. For theoretical clinical application, AWD should be therefore classified in ranges, defined by the maximum image resolution. Further experimental and human studies, especially combining AWD with aneurismal flow and shear stress simulations are needed, to better define the clinical role of AWD as risk factor for aneurysm rupture.