Assessing flow diverter porosity: a comparative analysis of quantification techniques based on imaging and simulation

Introduction Sizing flow diverters (FDs) can be challenging during cerebral aneurysm pre-treatment planning. FDs can differ from their labelled lengths by 30% after deployment because of changes in vessel curvature and diameter. 1 Current FD sizing tools do not account for vessel shape or predict device apposition. We present a pilot study to evaluate the use of computational modelling for FD sizing. The modelling software is based on the finite element approach and has been shown to simulate FD deployments that closely match clinical deployments. 2 Methods Twenty-four patient cases in three hospitals were selected for treatment with the pipeline embolization device. Twelve of the cases were pre-planned using the SurgicalPreView computational modeling software, while the remaining cases were conventionally planned. In the computationally modeled cases, each patient’s CT image data were uploaded to SurgicalPreView and re-constructed before treatment. The principal physician simulated deployment of 1–3 different FDs on the software and evaluated simulation results before treatment. After treatment, the physician filled out a questionnaire on the usefulness of the simulation results. Further, post-treatment image data for the 12 cases were used to compare simulated and clinical deployments. Results According to physician responses, computational modeling was useful for all cases and it improved confidence in device selection. In 58% of cases, simulation results changed the physician’s original device selection. In most cases, the physician selected a longer length device or a larger device diameter after evaluating simulation results. Limited effect was observed on operative time and the number of endovascular devices used. An example comparison between simulated and clinical deployments is shown in figure 1. Conclusion Overall, the pilot study showed improvements in FD pre-treatment planning using computational modeling. Simulation results helped physicians predict the behavior of FDs in tortuous vessels and with maximizing apposition. Pretreatment planning may reduce costs by shortening operative time and reducing the number of devices used. Improvements to FD selection can potentially lead to better patient outcomes. References Fernandez H, Macho J, Andaluz J, Serra L, Larrabide I. Braided device foreshortening. presented at the Computer Assisted Radiology and Surgery, 2014. Babiker H, et al. Clinical validations of simulated neurovascular braided stent deployments . presented at the Frontiers in Medical Devices Conference – Innovations in Modeling and Simulation: Patient-Centered Healthcare, Washington, DC, 2016. Disclosures B. Chong: 4; C; Endovantage LLC. B. Bendok: None. C. Krishna: None. M. Sattur: None. B. Brown: None. R. Tawk: None. D. Miller: None. L. Rangel-Castilla: None. G. Lanzino: None.

Robust optimization of geometrical properties of flow diverter stents for treating cerebral aneurysm: A proof-of-concept study

Flow diverters are widely extended in clinical practice for intracraneal aneurysms treatment. They are formed by a dense mesh of braided wires that partially occludes the aneurysm neck and restores the blood flow into the parent vessel. The occlusion degree is highly dependant on the distribution of the wires under the aneurysm, which is affected by the vessel geometry. Nowadays, there are no clinical indicators of the covering ratio once the flow diverter is deployed. We propose a novel method for the simulation of the flow diverter local porosity before its deployment into the parent vessel. We validate the method on curved silicon models, obtaining a correlation of 0.9 between the simulated values and the measured porosity on the deployed flow diverter.

BackgroundCerebral aneurysms, especially large and giant ones, pose challenges in neurointerventional surgery. Treatment choices involve clinical presentation, aneurysm details, and global resource variations. Neurointerventional methods, while innovative, may be cost-restrictive...

Objective To evaluate risk factors for acute ischemic stroke following treatment of paraclinoid aneurysms using flow diverters. Methods Between September 2015 and July 2018, 205 consecutive patients with 229 paraclinoid aneurysms were treated with Pipeline embolization device (PED) at Department of Interventional Neuroradiology, Beijing Tiantan Hospital, Capital Medical University. The aneurysm size and parent artery size were measured. According to the length, proximal and distal diameter of the parent artery, appropriate size of PED was deployed with or without coiling. Various potential risk factors associated with acute ischemic stroke following PED treatment were documented. Univariate and multivariate logistic regression analyses were applied to identify risk factors. Results Among the 205 patients with 229 paraclinoid aneurysms, 110 aneurysms were treated by PED and 119 aneurysms received PED with coiling, all PED were delivered and implanted successfully. Eighteen (8.8%) patients with 20 aneurysms had acute ischemic stroke after PED deployment. Univariate analysis suggested that ADP inhibition, high MA-ADP value, clopidogrel non-response, application of complex intraoperative techniques, and long operation time were associated with the acute ischemic stroke following PED treatment (all P<0.05). Further multivariate logistic regression analysis showed the clopidogrel non-response (OR=6.161, 95% CI: 1.480-25.649, P=0.012), application of complex intraoperative techniques (OR=8.405, 95% CI: 1.437-49.146, P=0.018) and operation time (OR=1.011, 95% CI: 1.002-1.020, P=0.022) were independent factors for acute ischemic stroke following PED treatment. Conclusions Clopidogrel non-response, application of complex intraoperative techniques and long operation time may increase the risk of ischemic events. Key words: Intracranial aneurysm; Stroke; Factor analysis, statistical; Flow diverter; Paraclinoid

Purpose: The Surpass NeuroEndograft (Surpass FD, Tel Aviv, Israel), a low porosity, high pore density flow diverting (FD) device, was evaluated for the treatment of intracranial aneurysms in a single center. Materials and Methods: A total of 45 aneurysms in 35 patients were treated. To achieve the calculated flow disruption between the parent artery and aneurysm and required for an occlusion, single devices, tailored to local boundary conditions, were placed endovascularly in parent arteries and covering the aneurysm. Implanted devices measured 2.9-5.3mm in diameter with a length of 10-50mm. Thirty-five aneurysms had complete neck coverage after implantation and ten bifurcation aneurysms had a planned incomplete neck coverage. Results: Six-month follow-up angiography available for 28 aneurysms with complete neck coverage, showed a complete occlusion in 27 aneurysms and a less than 50% occlusion in one, resulting in a 96% occlusion rate. Five aneurysms with incomplete neck coverage had complete occlusion at six months follow-up, and four had less than 50% occlusion. There were two parent artery occlusions, leading to a permanent stroke in one patient. There were no other permanent neurological morbidities and there was no mortalitiy., thus permanent morbidity in these series was 2,9%. Infarctions caused by occlusion of perforating arteries covered by the implant during the follow-up period were not seen. Conclusion: Preliminary data demonstrate in treatment of complex aneurysms the efficacy of a new generation of FD device.

Less than a decade ago AJNR published some of the first case studies of cerebral aneurysm hemodynamics using the then-novel combination of computational fluid dynamics (CFD) and 3D medical imaging. AJNR has since become the pre-eminent venue for such "image-based" or "patient-specific" CFD

A mathematical derivation of the porosity (local void fraction) distribution near the walls of packed beds of uniform spheres is presented. This investigation supports the study of methods of reducing or eliminating the so-called wall effect, or bypass flow, which accompanies the increase in porosity when spheres come in contact with a solid boundary. Limiting the amount of bypass flow is important in certain applications such as in packed bed nuclear reactors where bypass flow allows some coolant to avoid the high power density core region. Four basic porosity distributions are determined. The first investigates the case where spheres against a flat wall are packed in the tightest possible packing density. This density is then reduced by changing the sphere spacing until the minimum porosity matches that obtained experimentally. In the other cases, the effect of various ways of embedding spheres in the wall on the wall region porosity is examined. By partially embedding spheres in the wall, the porosity at the wall is reduced and the most direct cause of the bypass flow is thereby eliminated. The porosity is found by evaluating the ratio of the solid area to total area in a plane which is parallel to the wall. The local porosity is derived as a function of distance from the wall in the region within one-half a sphere diameter from the wall. The average porosity of the wall region is also calculated. This research has application to flow situations such as packed bed chemical reactors, pebble bed nuclear reactors and flow in packed beds.

Quantitative analysis of 3D pore characteristics effect on the ductility of HPDC Al–10Si-0.3 Mg alloy through X-ray tomography

The frequency-dependent conductivity and dielectric constant of a salt-water-saturated porous glass specimen have been measured. The measurements cover the full frequency range of the Maxwell–Wagner dispersion. The experimental results have been compared with the recently introduced local porosity theory and with previous theories. For the purpose of comparing with the local porosity theory experimental measurements of local porosity distributions from digitized pore space images are presented. These experimental porosity distributions are then used for a first experimental test of local porosity theory. The comparison with previous theoretical expressions for the frequency-dependent effective dielectric function shows that local porosity theory constitutes a significant improvement in the quantitative agreement.

The main reservoirs in the Linguado Field are grainstone and packstone carbonates composed of oolites, oncolites, pelloids, and rare bioclasts, of the Quissama Formation (Albian-age) and coquinas of the Coqueiros Formation (Aptian-age). Within Quissama Formation, facies have high porosity variations and their 3D characterization is of utter importance to allow for a better location of the wells. The objective of this study was a volumetric characterization of Quissama Formation by means of an adapted classical workflow composed of well-seismic tie, seismic preconditioning, seismic interpretation, seismic inversion, petrophysical properties estimation, and porosity geostatistical modeling. Seismic inversion results allowed the interpretation of a horizon to separate the carbonate platform in an upper zone, with low acoustic impedance, from a lower zone, with high acoustic impedance. Finally, behavioral knowledge of acoustic impedance and the porosity distribution within the Albian carbonate platform helped to better characterize the distribution of carbonaceous facies allowing the confirmation that commercial wells were drilled in low acoustic impedance and high porosity regions. It was also possible to confirm that a well, declared as noncommercial, was drilled in a poor reservoir region with high acoustic impedance and low porosity and identified other locations that were not yet drilled but could represent potential targets.

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IntroductionContrast usage for Cone Beam Angiographic Computed Tomography (CBCTA) performance has limited efficacy for simultaneous visualization of vasculature, implanted devices, and surrounding tissue. Optimal windowing of CBCTA images in order...

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.

Simulations using the patient-specific geometry of the aneurysm may help in a better planning of the treatment and in a consequent reduction of the associated risks. We propose, evaluate, and implement a methodology for the simulation of flow diverter (FD) devices in intracranial aneurysms by using a porous medium method (PMM), which greatly reduces the computational cost of these simulations compared with immersed method (IMM) approaches used to model complex FDs. The method relies on parameters from an empirical correlation derived from experimental observations in wire screens, consistent with CFD simulations. The verification of our PMM strategy was carried out by comparing the results of simulations in different (patient-specific) geometries and FDs, to those obtained under identical conditions by the IMM. Overall, both quantitative and qualitative results are consistent between IMM and PMM in cases where the local porosity remains roughly uniform throughout the neck, with differences in the reduction of the observables lower than 10%. This PMM strategy is up to 10 times faster than the IMM, which allows for a runtime of hours instead of days, bringing it closer for its application in the clinic.