Correlation Between The Rupture Risk And Virtual Wall Thickness Of Saccular Intracranial Aneurysms

ObjectiveTo explore the numerical simulation method of intracranial aneurysm "virtual wallthickness" based on individual aneurysm model, and to analyze the relationship between"virtual wall thickness" and rupture risk in order to provide theoretical basis for clinicalprevention and treatment of unruptured aneurysm.Methods1. Based on the head CTA DICOM images from patients with aneurysm,3D surfacemodel of aneurysm was established with VMTK (Vascular Modeling Toolkit) software andlevel set methods.2. The steps for the digital removal of a saccular cerebral aneurysm from its parentvasculature included: computing Voronoi Diagram from3D surface model, extractingcenter lines, interpolating centerline, clipping of Voronoi Diagram, interpolating VoronoiDiagram and reconstructing parent vessel model.3. After the parison and mould of aneurysm were processed in Geomagic Studiosoftware, they were imported into Gambit pre-processor to generate mesh, define theboundaries and domain. Computer numerical simulation of wall thickness distribution wascalculated using blow function in ANSYS POLYFLOW software.4. A series of3D surface model with changeable geometric parameters was set upusing Geomagic Studio reverse modeling software. The geometric parameters includedhighth, width, neck width and the volume of the aneurysm. The correlation between"virtual wall thickness" and geometric parameters was analyzed through changeable localgeometric models.5. The numerical simulation analysis of "virtual wall thickness" was performed in80ruptured and unruptured aneurysms, and the relationship between "virtual wall thickness"and rupture risk was assessed. Results1. The VMTK software can be used to establish3D surface model of aneurysmsuccessfully. By setting different parameters, some DICOM images with poor quality canalso be used to reconstruct and display micro geometry like small bleb on aneurysmsurface.2. The digital removal of a saccular cerebral aneurysm from its parent vasculature wascompleted through man-machine interactive way in the VMTK software and Pythonsoftware. The reconstructed model can be used in finite element model, mesh generationand numerical simulation.3. The parison and mould of aneurysm can be successfully imported into pre-processorto generate mesh, define boundaries and domain. Computer numerical simulation of wallthickness distribution was calculated in ANSYS POLYFLOW software successfully.4. Using the editing functions of reverse modeling software and semi-parametermethod, some series of3D surface model such as height variation model, width variationmodel, neck width variation model and volume variation model were establishedsuccessfully. The variation curve between "virtual wall thickness" and single geometricparameter displayed some rules and tendency.5. There were significant differences in "virtual wall thickness" between ruptured andunruptured aneurysms (P<0.05), and the area under ROC curve was0.807(95%confidence interval [CI],0.711-0.904).ConclusionsThe methods of "virtual wall thickness" numerical simulation were proved feasible."Virtual wall thickness" can be used to assess the risk of aneurysm rupture as an importantparameter.