Relationships of Morphologic Parameters and Hemodynamic Parameters Determined by Computational Fluid Dynamics Analysis with the Severity of Subarachnoid Hemorrhage

Abstract

Objective: The relationships of the results of hemodynamic evaluation of cerebral aneurysms using computational fluid dynamics (CFD) analysis with the occurrence, enlargement, rupture status, and intraoperative findings are studied, but there have been no reports on their relationship with the severity of subarachnoid hemorrhage (SAH). We, therefore, examined morphologic characteristics of cerebral aneurysms and hemodynamic characteristics based on CFD analysis and evaluated their relationships with the severity of SAH. Methods:Of the 200 consecutive cases of SAH encountered between 2007 and 2014, 119 cases of ruptured saccular aneurysms diagnosed by 3D-CTA using a 64-row multislice CT scanner within 72 hours after the onset were analyzed.They were classified according to the severity of the condition on admission using the World Federation of Neurosurgical Societies (WFNS) SAH grading scale (WFNSG) into mild (WFNSG1-3) and severe (WFNSG4-5) groups. Patient-specific statistical shape models were developed from 3D-CTA Digital Imaging and COmmunication in Medicine (DICOM) data, and steady-state analysis was performed by setting the end-diastolic physiologic blood flow volume according to the vascular luminal diameter as the entrance state. Morphologic evaluation was performed by calculating seven primary dimensions and four shape indexes from the morphologic data used for CFD analysis. As hemodynamic parameters, the wall shear stress (WSS), normalized WSS (NWSS), low shear area ratio (LSAR), flow velocity (FV), and invariant Q (IQ) were calculated. Statistical analysis was performed using the Mann-Whitney U-test at the P <0.05 level of significance.Results: After excluding 6 cases in which segmentation for CFD analysis was impossible, the remaining 113 cases were classified into 74 mild and 39 severe cases. No significant difference was observed in the morphologic parameters including the primary dimensions such as the maximum size or shape indexes such as the aspect ratio and size ratio between the mild and severe groups. Concerning the hemodynamic parameters, the WSS and NWSS were lower, and LSAR was larger, in the severe group than in the mild group, but the differences were not significant. On separate analysis of internal carotid (n = 44), middle cerebral (n = 31), and anterior communicating (n = 24) artery aneurysms, the parent artery diameter (PD) was smaller in the severe group than in the mild group in middle cerebral artery aneurysms (2.56 mm vs. 2.03 mm, P = 0.039). In the internal carotid artery aneurysms, the size ratio was significantly larger (2.04 vs. 2.38, P = 0.040), NWSS was lower (0.289 vs. 0.168, P = 0.033), and LSAR was larger (0.284 vs. 0.542, P = 0.035), in the severe group than in the mild group.Conclusion: CFD analysis using 3D-CTA in patients with severe ruptured cerebral aneurysms suggested characteristics including a small diameter of parent artery, a large shape index, and a low WSS.

Modern neuroradiological diagnostic methods for intracranial arterial aneurysms: a review

“…Моделирование на основе вычислительной гидродинамики должно основываться на целом ряде параметров, в частности на точной геометрии аневризмы, граничных условиях потока крови для конкретного пациента, реальной реологии крови и свойств стенок сосудов. Однако на практике из-за отсутствия указанных данных для конкретного пациента и во избежание высоких вычислительных затрат обычно принимается несколько допущений[18]. Эта практика вызывает опасения по поводу надежности результатов моделирования, влияя на ее внедрение в клинику.Опуская технические аспекты процесса моделирования потока крови, кратко остановимся на описании некоторых допущений и их влиянии на различные гемодинамические показатели.Одним из допущений вычислительной гидродинамики, в основе которого лежат данные диагностических изображений, является применение стандартных граничных значений потока крови на входе и выходе из зоны интереса, поскольку в текущей клинической практике измерения указанных показателей для каждого пациента обычно не проводятся.…”