Sunil Appanaboyina

Efficient pipeline for image-based patient-specific analysis of cerebral aneurysm hemodynamics: technique and sensitivity

Hemodynamic factors are thought to be implicated in the progression and rupture of intracranial aneurysms. Current efforts aim to study the possible associations of hemodynamic characteristics such as complexity and stability of intra-aneurysmal flow patterns, size and location of the region of flow impingement with the clinical history of aneurysmal rupture. However, there are no reliable methods for measuring blood flow patterns in vivo. In this paper, an efficient methodology for patient-specific modeling and characterization of the hemodynamics in cerebral aneurysms from medical images is described. A sensitivity analysis of the hemodynamic characteristics with respect to variations of several variables over the expected physiologic range of conditions is also presented. This sensitivity analysis shows that although changes in the velocity fields can be observed, the characterization of the intra-aneurysmal flow patterns is not altered when the mean input flow, the flow division, the viscosity model, or mesh resolution are changed. It was also found that the variable that has the greater impact on the computed flow fields is the geometry of the vascular structures. We conclude that with the proposed modeling pipeline clinical studies involving large numbers cerebral aneurysms are feasible.

Computational modelling of blood flow in side arterial branches after stenting of cerebral aneurysms

The major concern with the use of stents as flow diverters for the treatment of intracranial aneurysms is the potential occlusion of a perforating artery or other side branches which can cause ischemic strokes. This article presents image-based patient-specific models of stented cerebral aneurysms in which a small side artery has been jailed by the stent mesh. The results indicate that, because of the large resistances of the distal vascular beds which dominate the flow divisions among the different arterial branches, the flow reduction in jailed side branches is quite small even when a large percentage of the inlet area of these branches has been blocked. This suggests that unless the side branch is completely occluded, it will likely maintain its normal blood flow. Although this conclusion eases the concern of stenting cerebral aneurysms, a complete occlusion can still be caused depending on the conformability characteristics of the stents.

Simulation of Stent Deployment in Patient-Specific Cerebral Aneurysm Models for Their Hemodynamics Analysis

Cerebral aneurysms are a mayor cause of hemorrhagic stroke which is a highly significant and devastating disease. Currently there is an increased interest in using endovascular devices for flow diversion such as stents, for treating intracranial aneurysms [1]. Several studies have proven that the geometry and position of the stent in its deployed state play a mayor role in the way the blood flow is diverted. The design of flow diverters and the selection of the most appropriate device for a given aneurysm require a computational model to study the changes in the blood flow patterns after stenting. In this paper an innovative methodology for virtual deployment of stents within patient-specific anatomical models is presented. One remarkable property of this technique is the ability to easily interchange different stent designs within the same model in order to perform fast comparative characterizations.Copyright

Image-Based Analysis of Blood Flow Modification in Stented Aneurysms

Currently there is increased interest in the use of stents as flow diverters for the treatment of intracranial aneurysms, especially wide necked aneurysms that are difficult to treat by coil embolization or surgical clipping. This paper presents image-based patient-specific computational models of the hemodynamics in cerebral aneurysms before and after treatment with a stent alone, with the goal of better understanding the hemodynamic effects of these devices and their relation to the outcome of the procedures. Stenting of cerebral aneurysms is a feasible endovascular treatment option for aneurysms with wide necks that are difficult to treat with coils or by surgical clipping. However, this requires stents that are capable of substantially modifying the intra-aneurysmal flow pattern in order to cause thrombosis of the aneurysm. The results presented in this paper show that the studied stent was able to change significantly the hemodynamic characteristics of the aneurysm. In addition, it was shown that patient-specific computational models constructed from medical images are capable of realistically representing the in vivo hemodynamic characteristics observed during conventional angiography examinations before and after stenting. This indicates that these models can be used to better understand the effects of different stent designs and to predict the alteration in the hemodynamic pattern of a given aneurysm produced by a given flow diverter. This is important for improving current design of flow diverting devices and patient treatment plans.

Patient-specific modeling of intracranial aneurysmal stenting

Simulating blood flow around stents in intracranial aneurysms is important for designing better stents and to personalize and optimize endovascular stenting procedures in the treatment of these aneurysms. However, the main difficulty lies in the generation of acceptable computational grids inside the blood vessels and around the stents. In this paper, a hybrid method that combines body-fitted grid for the vessel walls and adaptive embedded grids for the stent is presented. Also an algorithm to map a particular stent to the parent vessel is described. These approaches tremendously simplify the simulation of blood flow past these devices. The methodology is evaluated with an idealized stented aneurysm under steady flow conditions and demonstrated in various patient-specific cases under physiologic pulsatile flow conditions. These examples show that the methodology can be used with ease in modeling any patient-specific anatomy and using different stent designs. This paves the way for using these techniques during the planning phase of endovascular stenting interventions, particularly for aneurysms that are difficult to treat with coils or by surgical clipping.

Flow Reduction in Jailed Arteries After Stenting of Cerebral Aneurysms

Recently, there has been increased interest in the use of flow divertion endovascular devices such as stents [1–3] to treat unruptured cerebral aneurysms. The goal of these devices is to deviate the blood flow away from the aneurysm and promote its thrombosis and exclusion from the circulation. However, one of the major concerns with these devices is the possibility of occluding a small arterial branch or perforating artery that may be jailed by the stent mesh. This could result in an ischemic stroke. The goal of this study was to assess the reduction in the flow rate in jailed side branches after stenting of cerebral aneurysms.Copyright

Techniques for Virtual Stenting of Intracranial Aneurysms

Intracranial aneurysms are pathological dilations of the arteries in the brain, whose rupture is often fatal. Surgery and endovascular embolization are the two most common methods of treatment. Surgery involves opening a portion of the skull and placing metallic clips at the aneurysm neck thereby preventing blood flow into the aneurysm. In the case of embolization, a catheter is used to pack platinum coils in the aneurysm reducing the inflow and promoting thrombus formation. Due to its less invasive approach endovascular embolization is preferred over surgery. Nevertheless this approach also has some serious aftereffects. Coil compaction followed by the re-growth or the formation of the secondary aneurysm is the most common problem. The endovascular embolization approach also has a serious shortcoming that the coils alone cannot be used to block every type of aneurysm. Wide neck or fusiform aneurysms are coiled with the help of stents. Recent studies show that stent, which is a hollow cylindrical mesh, can be successfully used to limit the flow of blood into the aneurysm. However these studies have been conducted using idealized in-vitro and numerical models. Studies conducted using patient-specific models generated from medical images will provide a more realistic approach to computationally investigate the effects of stents on intra-aneurysmal flow patterns. However generation of computational grids inside the parent vessel and around these stents is a challenging task. In this paper an algorithm to map the stent to a patient-specific vascular model and an adaptive unstructured embedded gridding technique to model flow around stents are presented. Finally these techniques are demonstrated on patient-specific cases to prove their feasibility.Copyright

Simulation of endovascular interventions of cerebral aneurysms: techniques and evaluation

Computer simulations of blood flow past endovascular devices such as coils and stents is important to design better devices as well as for personalizing and optimizing endovascular procedures used to treat cerebral aneurysms. However, the main difficulty lies in the generation of suitable computational grids inside the blood vessels and around the surface of these devices. In this paper, a hybrid method that combines body fitted grids for the vessel walls and adaptive embedded grids for the devices is presented. This approach tremendously simplifies the simulation of blood flows past endovascular devices. The methodology is evaluated with a simple flow past a circular cylinder and illustrated with several idealized aneurysm stenting models and a subject-specific model of aneurysm coiling. These examples demonstrate that the methodology can be used in a wide variety of interesting applications with different levels of geometrical complexity with only a modest increase in effort. This paves the way for using these techniques to evaluate different terapeutic options during the planning phase of endovascular interventions.