Explore the vast range of titles available.

Cerebral aneurysms are a serious clinical challenge, with ∼half resulting in death or disability. Treatment via endovascular coiling significantly reduces the chances of rupture, but the techniquehas failure rates of ∼20 %. This presents a pressing need to develop a method fordetermining optimal coildeploymentstrategies. Quantification of the hemodynamics of coiled aneurysms using computational fluid dynamics (CFD) has the potential to predict post-treatment outcomes, but representing the coil mass in CFD simulations remains a challenge. We use the Finite Element Method (FEM) for simulating patient-specific coil deployment for n = 4 ICA aneurysms for which 3D printed in vitro models were also generated, coiled, and scanned using ultra-high resolution synchrotron micro-CT. The physical and virtual coil geometries were voxelized onto a binary structured grid and porosity maps were generated for geometric comparison. The average binary accuracy score is 0.8623 and the average error in porosity map is 4.94 %. We then conduct patient-specific CFD simulations of the aneurysm hemodynamics using virtual coils geometries, micro-CT generated oil geometries, and using the porous medium method to represent the coil mass. Hemodynamic parameters including Neck Inflow Rate (Qneck) and Wall Shear Stress (WSS) were calculated for each of the CFD simulations. The average relative error in Qneck and WSS from CFD using FEM geometry were 6.6 % and 21.8 % respectively, while the error from CFD using a porous media approximation resulted in errors of 55.1 % and 36.3 % respectively; demonstrating a marked improvement in the accuracy of CFD simulations using FEM generated coil geometries.

Flow-diverting stents (FDS) are used to treat cerebral aneurysms. They promote the formation of a stable thrombus within the aneurysmal sac and, if successful, isolate the aneurysmal dome from mechanical stresses to prevent rupture. Platelet activation, a mechanism necessary for thrombus formation, is known to respond to biomechanical stimuli, particularly to the platelets’ residence time and shear stress exposure. Currently, there is no reliable method for predicting FDS treatment outcomes, either a priori or after the procedure. Eulerian computational fluid dynamic (CFD) studies of aneurysmal flow have searched for predictors of endovascular treatment outcome; however, the hemodynamics of thrombus formation cannot be fully understood without considering the platelets’ trajectories and their mechanics-triggered activation. Lagrangian analysis of the fluid mechanics in the aneurysmal vasculature provides novel metrics by tracking the platelets’ residence time (RT) and shear history (SH). Eulerian and Lagrangian parameters are compared for 19 patient-specific cases, both pre- and post-treatment, to assess the degree of change caused by the FDS and subsequent treatment efficacy.

Minimally-invasive therapies are well-established treatment methods for saccular intracranial aneurysms (SIAs). Knowledge concerning fusiform IAs (FIAs) is low, due to their wide and alternating lumen and their infrequent occurrence. However, FIAs carry risks like ischemia and thus require further in-depth investigation. Six patient-specific IAs, comprising three position-identical FIAs and SIAs, with the FIAs showing a non-typical FIA shape, were compared, respectively. For each model, a healthy counterpart and a treated version with a flow diverting stent were created. Eighteen time-dependent simulations were performed to analyze morphological and hemodynamic parameters focusing on the treatment effect (TE). The stent expansion is higher for FIAs than SIAs. For FIAs, the reduction in vorticity is higher (Δ35–75% case 2/3) and the reduction in the oscillatory velocity index is lower (Δ15–68% case 2/3). Velocity is reduced equally for FIAs and SIAs with a TE of 37–60% in FIAs and of 41–72% in SIAs. Time-averaged wall shear stress (TAWSS) is less reduced within FIAs than SIAs (Δ30–105%). Within this study, the positive TE of FDS deployed in FIAs is shown and a similarity in parameters found due to the non-typical FIA shape. Despite the higher stent expansion, velocity and vorticity are equally reduced compared to identically located SIAs.

Due to their effect on aneurysm hemodynamics, flow diverters (FD) have become a routine endovascular therapy for intracranial aneurysms. Since over- and undersizing affect the device’s hemodynamic abilities, selecting the correct device diameter and accurately simulating FD placement can improve patient-specific outcomes. The purpose of this study was to validate the accuracy of virtual flow diverter deployments in the novel Derivo® 2 device. We retrospectively analyzed blood flows in ten FD placements for which 3D DSA datasets were available pre- and post-intervention. All patients were treated with a second-generation FD Derivo® 2 (Acandis GmbH, Pforzheim, Germany) and post-interventional datasets were compared to virtual FD deployment at the implanted position for implanted stent length, stent diameters, and curvature analysis using ANKYRAS (Galgo Medical, Barcelona, Spain). Image-based blood flow simulations of pre- and post-interventional configurations were conducted. The mean length of implanted FD was 32.61 (±11.18 mm). Overall, ANKYRAS prediction was good with an average deviation of 8.4% (±5.8%) with a mean absolute difference in stent length of 3.13 mm. There was a difference of 0.24 mm in stent diameter amplitude toward ANKYRAS simulation. In vessels exhibiting a high degree of curvature, however, relevant differences between simulated and real-patient data were observed. The intrasaccular blood flow activity represented by the wall shear stress was qualitatively reduced in all cases. Inflow velocity decreased and the pulsatility over the cardiac cycle was weakened. Virtual stenting is an accurate tool for FD positioning, which may help facilitate flow FDs’ individualization and assess their hemodynamic impact. Challenges posed by complex vessel anatomy and high curvatures must be addressed.

Modeling blood flow in aneurysms treated with coils could be used to understand the complete embolization of the aneurysm, through thrombus formation that fills the entire sac. Modeling of the endovascular coil mass as a porous medium is a technique that allows for study of aneurysm hemodynamics, efficiently for patient-specific treatment outcome predictions. Models in the literature use mean porosity of coils in the aneurysmal volume, proving inadequate for outcome prediction. However, models that consider heterogeneous porosity distribution have shown more accurate hemodynamics. We recently published the porous crown model, considering the heterogeneous coil mass distribution, validated on two patients. This study aims (i) to validate the porous crown model for a larger cohort (eight patients), and (ii) to propose a porous medium model translatable to clinical practice in treatment planning. We analyzed the porosity distribution of the endovascular coils deployed inside the cerebral aneurysm phantoms of eight patients using 3D x-ray synchrotron images. The permeability and inertial factor of the porous crown model are calculated using previously published methodology. We propose a new “bilinear” porous model, that uses the same hypothesis, but the permeability and inertial factor can be defined from just basic information available in the neuro-suite, i.e., the aneurysmal sac volume and the coil volume fraction targeted by the neurosurgeon. These two models are compared to the coil-resolved simulations, considered as the gold standard. The results show that both the porous crown model and the bilinear model produce similarly accurate hemodynamics in the aneurysm. The error in the standard (mean porosity) porous model is 66%, whereas the error of the bilinear model is 26%, compared to the coil-resolved. The bilinear model is promising as a means of treatment outcome prediction at time of intervention.

Intracranial aneurysms are dilated portions of an artery that supplies blood to the brain. These abnormal dilatations of the arterial wall carry the risk of rupture, which represents a leading cause of subarachnoid hemorrhage and have very high mortality and morbidity. Endovascular therapies are deployed by neurointerventionalists to treat intracranial aneurysms, reducing further growth and the risk of rupture. The success of these therapies involves the cessation of blood flow into the aneurysmal cavity, because of a clot fully occluding the aneurysm, allowing reendothelialization of the parent vessel. If there is any remnant flow, the treatment is considered unsuccessful and may warrant retreatment.While both coil embolization devices and flow-diverting stents (FDS) are proven endovascular therapies, there is no way to predict the treatment outcome in either of two treatment modalities, whether using pre- or post-operative information. The patient is therefore required to return for medical imaging to determine the outcome, which increases the burden on the healthcare system, as well as the procedural and rupture risk of the patient. The inability to predict treatment outcome can be addressed with the use of computational fluid dynamics (CFD). While many studies have been conducted with small patient populations, the use of CFD to understand the evolution of intracranial aneurysm has yet to identify thresholds for hemodynamics metrics to predict treatment outcomes, or even which metrics are physiologically relevant. Standard image-based patient-specific CFD simulations rely on a variety of models to account for the effect of treatment on hemodynamics. Unfortunately, a lack of standardization and automation, coupled with the uncertainty associated with many of the models used historically for their simplicity without a rigorous validation of their accuracy, has led to a lack of consensus on which hemodynamics metrics should be studied for their predictive potential.This dissertation investigates two main forms of endovascular therapy of cerebral aneurysms: coils and FDS, via a computational simulation framework that introduces novel models and validates them against gold-standard, experimentally-derived coil- and stent-resolved simulations. The overall goal is to contribute to the state-of-the-art simulation framework to move CFD towards becoming a clinical standard of care tool. The first question addressed is whether the two devices can be considered analogous when seeking metrics that are predictive of outcomes. The follow-up question is whether a new framework for studying the hemodynamics of intraaneurysmal flow and potential thrombosis, Lagrangian particle tracking, can shed light on the physiological processes that determine aneurysm embolization, and success post-treatment. As a side project, during my Fullbright stay at the Otto Von Guericke University in Magdeburg, Germany, I considered the differences between saccular and fusiform aneurysms and how the hemodynamics and FDS deployment differ for these two phenotypes. Finally, my last contribution is the evaluation of a new porous media model, used to model the coil mass comparing it to coil-resolved simulations to determine its efficacy in predicting Eulerian and Lagrangian metrics.

This volume provides an in-depth account of Old English, organized by linguistic level. Individual chapters, written by recognized experts in the field, review the state of the art in phonological, morphological, syntactic, and semantic studies of Old English. Key areas of debate, including dialectology, language contact, standardization, and literary language, are also explored. The volume sets the scene with a chapter on pre-Old English and ends with a chapter discussing textual resources available for the study of earlier English.

Our purpose was to conduct a customer satisfaction survey of verbal responses provided by a pharmaceutical company's third-party medical information (MI) call center. One survey for health care providers (HCPs) and one for consumers were designed to assess customer satisfaction following a verbal response to an MI question. Surveys were offered to all HCPs and consumers contacting the MI call center January-March 2007. Respectively, 27% and 18% of all HCPs and consumers (N = 318) receiving a verbal response agreed to participate. The completeness and understanding of medical responses were rated similarly, independent of caller type, 92% rating the answer received as complete and 98%> rating the quality as above average to excellent. Additionally, 53% of HCPs rated the response quality as better than that provided by other industry call centers. Lastly, 100% of both caller types stated they were treated in a courteous or professional manner. Based on the three-month customer satisfaction survey, the medical information and level of professionalism provided by the call center were average to above average, indicating a high level of customer satisfaction with verbal responses.

To enhance medical information (MI) support of the sales force, two online surveys were designed: an external survey to identify general avenues for improvement and an internal survey to identify specific opportunities for improvement. The external survey was disseminated to 86 MI departments to determine standard MI practices in support of sales representatives. The internal survey assessing sales representative satisfaction with existing MI services was disseminated to 778 Solvay Pharmaceuticals Inc sales representatives. Both surveys were sent in December 2007 and remained open through January 2008. Eighteen MI departments (21%) responded to the external survey and 420 sales representatives (54%) responded to the internal survey. Results from these surveys suggested several considerations for the enhancement of MI support of the sales force.