A (Near) Real-Time Simulation Method of Aneurysm Coil Embolization

International audienceA (Near) Real-Time Simulation Method of Aneurysm Coil Embolizatio

Numerical study of a thrombus migration risk in aneurysm after coil embolization in patient cases: FSI modelling

Purpose There are still many challenges for modelling a thrombus migration process in aneurysms. The main novelty of the present research lies in the modelling of aneurysm clot migration process in a realistic cerebral aneurysm, and the analysis of forces sufered by clots inside an aneurysm, through transient FSI simulations. Methods The blood fow has been modelled using a Womersley velocity profle, and following the Carreau viscosity model. Hyperelastic Ogden model has been used for clot and isotropic linear elastic model for the artery walls. The FSI coupled model was implemented in ANSYS® software. The hemodynamic forces sufered by the clot have been quantifed using eight diferent clot sizes and positions inside a real aneurysm. Results The obtained results have shown that it is almost impossible for clots adjacent to aneurysm walls, to leave the aneurysm. Nevertheless, in clots positioned in the centre of the aneurysm, there is a real risk of clot migration. The risk of migration of a typical post-coiling intervention clot in an aneurysm, in contact with the wall and occupying a signifcant percentage of its volume is very low in the case studied, even in the presence of abnormally intense events, associated with sneezes or impacts. Conclusions The proposed methodology allows evaluating the clot migration risk, vital for evaluating the progress after endovascular interventions, it is a step forward in the personalized medicine, patient follow-up, and helping the medical team deciding the optimal treatment.Universidade de Vigo/CISU

A Comprehensive Numerical Approach to Coil Placement in Cerebral Aneurysms: Mathematical Modeling and In Silico Occlusion Classification

Endovascular coil embolization is one of the primary treatment techniques for cerebral aneurysms. Although it is a well established and minimally invasive method, it bears the risk of sub-optimal coil placement which can lead to incomplete occlusion of the aneurysm possibly causing recurrence. One of the key features of coils is that they have an imprinted natural shape supporting the fixation within the aneurysm. For the spatial discretization our mathematical coil model is based on the Discrete Elastic Rod model which results in a dimension-reduced 1D system of differential equations. We include bending and twisting responses to account for the coils natural curvature. Collisions between coil segments and the aneurysm-wall are handled by an efficient contact algorithm that relies on an octree based collision detection. The numerical solution of the model is obtained by a symplectic semi-implicit Euler time stepping method. Our model can be easily incorporated into blood flow simulations of embolized aneurysms. In order to differentiate optimal from sub-optimal placements, we employ a suitable in silico Raymond-Roy type occlusion classification and measure the local packing density in the aneurysm at its neck, wall-region and core. We investigate the impact of uncertainties in the coil parameters and embolization procedure. To this end, we vary the position and the angle of insertion of the microcatheter, and approximate the local packing density distributions by evaluating sample statistics

Vascular Malformations of the Central Nervous System

Vascular malformations of the central nervous system are important pathologies that could present with abrupt onset hemorrhage resulting in devastating neurological deficits. Current knowledge of their biology and natural history is increasing. Diagnostic modalities help clinicians to better evaluate the individual cases, and to decide the best treatment options. Treatment alternatives are various and all treatment options should be evaluated before choosing the final therapeutic modality. The purpose of this book is to review the current knowledge about vascular malformations of the central nervous system and to evaluate the treatment alternatives

Investigation of Polyurethane Shape Memory Polymer for Potential Applications in Brain Aneurysm Treatment

Intracranial aneurysms (ICAs) are abnormal deformations in the walls of cranial arteries that can rupture, resulting in hemorrhage and stroke. Modern ICA treatments minimize the risk of rupture by limiting blood flow into the aneurysm body, but current treatments are limited in their ability to provide long-term solutions for large and/or complex aneurysm geometries. Self-deploying devices made from porous shape memory polymer (SMP) materials could improve ICA treatment by allowing for a more stable and uniform occlusion of the aneurysm sac. This thesis discusses investigations into the chemical composition, physical structure, and manufacture of a polyurethane shape memory polymer (SMP) with potential applications in the design of an alternative ICA treatment device. The investigation demonstrates 1) composition dependent activation temperature and mechanical properties that can be tuned for medical applications, 2) a particle leaching synthesis procedure for the production of uniform open-cell SMP foam structures with high compressibility, and 3) a novel direct ink writing 3D printer prototype compatible with the thermoset polyurethane SMP material

Design, Fabrication, and Characterization of a Shape Memory Polymer Embolic Device

Shape memory polymers (SMPs) are a unique class of smart materials that can remember two shapes, and can be remotely actuated to achieve a predefined shape by application of thermal energy. Porous scaffold of SMP foams enable high volume change up to 70 times. Use of these SMP foams in a minimally invasive treatment of cerebral aneurysms is of significant interest in the biomedical community. In the application of treating aneurysms, a spheroid SMP foam is envisioned to be compressed to a rod-like cylindrical secondary shape. The device in this secondary shape can then be delivered through a catheter to the aneurysm site and, once in the aneurysm, can be actuated to recover the primary shape to fill the aneurysmal protuberance. Blood is expected to infiltrate and clot within the porous internal structure of the expanded SMP foam, ultimately leading to complete isolation of the aneurysm from the parent artery through tissue healing. This study reports the functional characterization of SMP foam with respect to the design and the fabrication of the prototype embolic device for treatment of cerebral aneurysms. The pressure exerted by the expanding SMP foam on the aneurysms wall during the occlusion is estimated. Frictional loads between SMP foam and a catheter pathway are investigated. This is a critical factor in the feasibility of transcatheter delivery of a SMP foam device. Porcine in vitro and in vivo aneurysm models are used to test and validate the deployment process of the proposed device. Important aspects are studied and discussed, such as deliverability through a catheter, recovery of the primary shape by thermal actuation, and fluoroscopic visualization of the device during the delivery. Finally, the performance of SMP embolic device, which is the endovascular delivery and the occlusion of porcine aneurysms, are compared to performance of Guglielmi Detachable Coil that is considered as the standard treatment. 90 and 180 days follow-up studies present promising healing responses of the SMP treated aneurysm. This study forms an important step towards the realization of these devices in clinical practice

Development of a static bioactive stent prototype and dynamic aneurysm-on-a-chip(TM) model for the treatment of aneurysms

Aneurysms are pockets of blood that collect outside blood vessel walls forming dilatations and leaving arterial walls very prone to rupture. Current treatments include: (1) clipping, and (2) coil embolization, including stent-assisted coiling. While these procedures can be effective, it would be advantageous to design a biologically active stent, modified with magnetic stent coatings, allowing cells to be manipulated to heal the arterial lining. Further, velocity, pressure, and wall shear stresses aid in the disease development of aneurysmal growth, but the shear force mechanisms effecting wound closure is elusive. Due to these factors, there is a definite need to cultivate a new stent device that will aid in healing an aneurysm insitu. To this end, a static bioactive stent device was synthesized. Additionally, to study aneurysm pathogenesis, a lab-on-a-chip device (a dynamic stent device) is the key to discovering the underlying mechanisms of these lesions. A first step to the reality of a true bioactive stent involves the study of cells that can be tested against the biomaterials that constitute the stent itself. The second step is to test particles/cells in a microfluidic environment. Therefore, biocompatability data was collected against PDMS, bacterial nanocellulose (BNC), and magnetic bacterial nanocellulose (MBNC). Preliminary static bioactive stents were synthesized whereby BNC was grown to cover standard nitinol stents. In an offshoot of the original research, a two-dimensional microfluidic model, the Aneurysm-on-a-ChipTM (AOC), was the logical answer to study particle flow within an aneurysm sac - this was the dynamic bioactive stent device. The AOC apparatus can track particles/cells when it is coupled to a particle image velocimetry software (PIV) package. The AOC fluid flow was visualized using standard microscopy techniques with commercial microparticles/cells. Movies were taken during fluid flow experiments and PIV was utilized to monito

Computational and Experimental Evaluation of Actuating Shape Memory Polymer Foams in the Context of Aneurysm Treatment

Shape memory polymer foams may be used to treat vascular aneurysms through thermal actuation of the foam from a compacted to an expanded configuration within the aneurysm structure, thereby alleviating blood pressure on the weakened aneurysm walls and reducing potential for rupture. After delivery to the aneurysm site, fiber-delivered laser light absorbed by the foam structure is converted into thermal energy, and actuation of the foam results. Introduction of nonphysiological energy into the body during foam actuation necessitates an evaluation of potential thermal damage to nearby tissue. In the present investigation, the foam is idealized as a heat-dissipating, volumetrically static object centered in a straight tube of flowing water. Velocity profiles around the heat-dissipating device are acquired experimentally with particle image velocimetry. A computational fluid dynamics package is then used to predict the experimental velocity profiles and temperature distributions by numerical solution of the Navier-Stokes and energy equations, and agreement between the computational solution and experimental results is assessed. Discussion of this assessment, as well as several preliminary procedures leading up to the creation of the heat-dissipating device and critical analysis of the methods employed, is also given. PIV and CFD are found to be in reasonable agreement with one another. Using laser-induced fluorescence as a temperature measurement modality, which is discussed in the text insofar as the technique was attempted several times and failed, together with PIV and CFD provides a formidable array of techniques exists to characterize flow around a heated device