In vitro digital subtraction angiographic evaluation of flow diverters in a patient-specific aneurysm.

Background The importance of both porosity and pore density of a flow diverter is well recognized in treatment of intracranial aneurysms; however, understanding of the effect of individual wire (wire number and size) is critical in improving device design and use. Methods A total of 10 multi-layered flow diverters with different wire numbers (32, 48, 56, and 72) and sizes (30, 35, and 40 µm) were implanted into identical patient-specific middle cerebral artery aneurysm models. Digital subtraction angiography was acquired at 30 f/s and X-ray signals at three selected regions of interest were compared to determine the amount of intra-aneurysmal flow.

In vitro investigation of contrast flow jet timing in patient-specific intracranial aneurysms.

Background: The direction and magnitude of intra-aneurysmal flow jet are significant risk factors of subarachnoid hemorrhage, and the change of flow jet during an endovascular procedure has been used for prediction of aneurysm occlusion or whether an additional flow diverter (FD) is warranted. However, evaluation of flow jets is often unreliable due to a large variation of flow jet on the digital subtraction angiograms, and this flow pattern variation may result in incorrect clinical diagnosis Therefore, factors contributing to the variation in flow jet are examined at an in vitro setting, and the findings can help us to understand the nature of flow jet and devise a better plan to quantify the aneurysmal hemodynamics accurately.

Methods: Intra-aneurysmal flows in three patient-specific aneurysms between 11 and 25 mm were investigated in vitro, and a FD was deployed in each aneurysm model.

Metal coverage ratio of pipeline embolization device for treatment of unruptured aneurysms: Reality check.

Background And Purpose: The metal coverage ratio (MCR) of a flow diverter influences the intra-aneurysmal hemodynamics; a high MCR will occlude an aneurysm early, while a low MCR may delay aneurysm occlusion. The true MCR of a pipeline embolization device (PED) could be lower due to oversize, device deformation, or aneurysm location. In this study deviation of the true MCR from the nominal MCR is assessed and whether their difference affects aneurysm occlusion rate is determined.

Extensive bilateral vertebral artery remodeling following treatment of dissection using pipeline embolic device.

Background: Cerebral artery dissection remains a significant cause of stroke, and the mainstay of treatment has been medical management with anticoagulation, although flow-diverting stents have been used in some cases of arterial dissection resistant to medical management.

Methods: We present a case report of bilateral vertebral artery stenting using pipeline embolic device flow-diverting stents, after failed medical management of the dissection.

Results: This case demonstrated substantial subsequent vertebral arterial remodeling and good clinical outcome with maintenance of posterior circulation.

Retrieval of distorted pipeline embolic device using snare-loop.

Background: Flow-diverter stents are increasingly being used in the endovascular treatment of intracranial aneurysms. Because of this increased usage, the occurrence of stent malpositioning, intra-arterial distortion, or migration will likely increase as well.

Methods: We describe the conformational twisting and deformity of a pipeline embolic device (PED) stent (Covidien, EV3) within the carotid artery during stent placement, with the subsequent immediate removal of the stent by using an endovascular snare-loop to successfully remove the device.

Hemodynamics of small aneurysm pairs at the internal carotid artery.

Cerebral aneurysms carry significant risks because rupture-related subarachnoid hemorrhage leads to serious and often fatal consequences. The rupture risk increases considerably for multiple aneurysms. Multiple aneurysms can grow from the same location of an artery, and the interaction between these aneurysms raises the rupture risk even higher.

Hemodynamic effect of Neuroform stent on intimal hyperplasia and thrombus formation in a carotid aneurysm.

Stents play an important role in management of cerebral aneurysms. A stent reconstructs the parent artery, assists coil embolization, and decreases flow activity within an aneurysm. However, an in-stent stenosis often occurs within the stented artery and compromises the circulation at the parent artery.

Timing and size of flow impingement in a giant intracranial aneurysm at the internal carotid artery.

Flow impingement is regarded as a key factor for aneurysm formation and rupture. Wall shear stress (WSS) is often used to evaluate flow impingement even though WSS and impinging force are in two different directions; therefore, this raises an important question of whether using WSS for evaluation of flow impingement size is appropriate. Flow impinging behavior in a patient-specific model of a giant aneurysm (GA) at the internal carotid artery (ICA) was analyzed by computational fluid dynamics simulations.

Cross-flow at the anterior communicating artery and its implication in cerebral aneurysm formation.

The anterior communicating artery (ACoA) is an important element of the circle of Willis. While the artery itself is short and small, a large number of intracranial aneurysms can be found at the ACoA. Four subject-specific ACoA models are constructed from 3D rotational angiographic images.

Hemodynamic relationship between intracranial aneurysm and carotid stenosis: review of clinical cases and numerical analyses.

Objective: Coexistence of both an intracranial aneurysm and a stenosis at the same internal carotid artery is infrequent, but it may complicate therapeutic management of either disease. It is unclear if a stenosis plays any role in development of intracranial aneurysms. We study patients with intracranial aneurysms at our hospital and investigate if there is a relationship between a carotid stenosis and an intracranial aneurysm.

Indirect measurement of aneurysm wall thickness using digital stethoscope.

Objective: No existing in vivo technique can measure aneurysm wall thickness for evaluation of rupture risk. Intracranial aneurysms produce bruits at a special range of frequency that are highly influenced by the wall thickness. Understanding of the mechanism that generates bruits may allow us to learn aneurysm behavior non-invasively.

Growth rate and rupture rate of unruptured intracranial aneurysms: a population approach.

Background: Understanding aneurysm growth rate allows us to predict not only the current rupture risk, but also accumulated rupture risk in the future. However, determining growth rate of unruptured intracranial aneurysms often requires follow-up of patients for a long period of time so that significant growth can be observed and measured. We investigate a relationship between growth rate and rupture rate and develop a theoretical model that can predict average behavior of unruptured intracranial aneurysms based on existing clinical data.

Estimating the hemodynamic impact of interventional treatments of aneurysms: numerical simulation with experimental validation: technical case report.

Objective: The goal of this study was to use phase-contrast magnetic resonance imaging and computational fluid dynamics to estimate the hemodynamic outcome that might result from different interventional options for treating a patient with a giant fusiform aneurysm.

Methods: We followed a group of patients with giant intracranial aneurysms who have no clear surgical options. One patient demonstrated dramatic aneurysm growth and was selected for further analysis.

Correlation between lumenal geometry changes and hemodynamics in fusiform intracranial aneurysms.

Background And Purpose: Hemodynamics may predispose aneurysms to rupture; however, hemodynamic descriptors that can describe aneurysm growth are not well understood. We examined the relationship between hemodynamics and growth of 2 fusiform basilar artery aneurysms in an effort to define hemodynamic variables that may be helpful in predicting aneurysmal growth.

Methods: Two patients with basilar fusiform aneurysms of a similar size were followed for a 2-year period.

Numerical simulation of magnetic resonance angiographies of an anatomically realistic stenotic carotid bifurcation.

Magnetic Resonance Angiography (MRA) has become a routine imaging modality for the clinical evaluation of obstructive vascular disease. However, complex circulatory flow patterns, which redistribute the Magnetic Resonance (MR) signal in a complicated way, may generate flow artifacts and impair image quality. Numerical simulation of MRAs is a useful tool to study the mechanisms of artifactual signal production.

Transport of contrast agents in contrast-enhanced magnetic resonance angiography.

Contrast-enhanced magnetic resonance angiography (CEMRA) often appears to display vessels with good resolution, but it does not adequately visualize the throat of a tight stenosis. Image quality in CEMRA is also governed by the timing of contrast injection and data acquisition. We developed a numerical technique to predict the image appearance of a target vessel by taking into account the passage of contrast agent.

Computational approach to quantifying hemodynamic forces in giant cerebral aneurysms.

Background And Purpose: The options for treating giant fusiform basilar aneurysms are limited, and the potential impact of planned interventions is difficult to assess. We developed a computational framework to evaluate the impact that interventions might have on hemodynamic conditions.

Methods: A computational fluid dynamics approach was used to determine the velocity field, wall shear stress, and pressure distribution within a model of a basilar artery before and after a simulated occlusion of one vertebral artery.