Characterization of cerebral aneurysms for assessing risk of rupture by using patient-specific computational hemodynamics models

Abstract

Background and purpose: Hemodynamic factors are thought to play an important role in the initiation, growth, and rupture of cerebral aneurysms. This report describes a pilot clinical study of the association between intra-aneurysmal hemodynamic characteristics from computational fluid dynamic models and the rupture of cerebral aneurysms.

Methods: A total of 62 patient-specific models of cerebral aneurysms were constructed from 3D angiography images. Computational fluid dynamics simulations were performed under pulsatile flow conditions measured on a normal subject. The aneurysms were classified into different categories, depending on the complexity and stability of the flow pattern, the location and size of the flow impingement region, and the size of the inflow jet. The 62 models consisted of 25 ruptured and 34 unruptured aneurysms and 3 cases with unknown histories of hemorrhage. The hemodynamic features were analyzed for associations with history of rupture.

Results: A large variety of flow patterns was observed: 72% of ruptured aneurysms had complex or unstable flow patterns, 80% had small impingement regions, and 76% had small jet sizes. By contrast, unruptured aneurysms accounted for 73%, 82%, and 75% of aneurysms with simple stable flow patterns, large impingement regions, and large jet sizes, respectively. Aneurysms with small impingement sizes were 6.3 times more likely to have experienced rupture than those with large impingement sizes (P = .01).

Conclusions: Image-based patient-specific numeric models can be constructed in an efficient manner that allows clinical studies of intra-aneurysmal hemodynamics. A simple flow characterization system was proposed, and interesting trends in the association between hemodynamic features and aneurysmal rupture were found. Simple stable patterns, large impingement regions, and jet sizes were more commonly seen with unruptured aneurysms. By contrast, ruptured aneurysms were more likely to have disturbed flow patterns, small impingement regions, and narrow jets.

Fig 1.

Physiologic flow conditions derived from PC-MR measurements on a normal subject. A, MRA. B, Vessels of the circle of Willis and location of PC-MR section planes. C, Magnitude image of PC-MR measurement. D, Phase image of PC-MR measurement. E, Flow rate curve obtained from the PC-MR measurement on the right internal carotid artery.

Fig 2.

Construction of a patient-specific vascular CFD model. A, Original 3DRA image. B, Smoothed image. C, Segmented image. D, Initial vascular reconstruction. E, Vessel geometry after deformable model and interactive truncation of arterial branches. F, Finite element grid. G, Peak pressure distribution. H, Mean wall shear stress distribution. I, Definition of cut plane used to visualize velocity pattern. J–L, Intra-aneurysmal flow velocity on cut plane at different instants during the cardiac cycle.

Fig 3.

Examples of aneurysms where the inflow jet impacts the neck (A), the body (B), or the dome (C) or has a changing impingement region (D). Images, from left to right, present volume rendering of 3DRA image, reconstructed model, mean wall shear stress distribution, and intra-aneurysmal flow velocity on a planar cut through the sac at 4 instants during the cardiac cycle.

Fig 4.

Examples of aneurysms with inflow jet located in the distal (A) and proximal (B) region of the neck. Images, from left to right, present volume rendering of 3DRA image, reconstructed model, and intra-aneurysmal flow velocity on a planar cut through the sac at 3 instants during the cardiac cycle.

Fig 5.

Schematic drawings of the most prominent flow structures observed in small (left) and large (right) aneurysms with flow types I (top) through IV (bottom). Arrows indicate the direction of flow at 3 instants during the cardiac cycle and illustrate the complexity and stability of the intra-aneurysmal flow patterns for the 4 flow type categories.

Fig 6.

Examples of small and large impact zones. A and B, Ruptured aneurysms with small flow impingement regions. C and D, Unruptured aneurysms with large impact zones. Red arrows indicate the flow impingement region.