Flow Redirection Research Articles

Case Report: Removal of septal occluder device and closure of atrial septal defect with pulmonary vein flow redirection

BACKGROUND: Atrial septal defect represents 10 to 15% of congenital heart disease and is more frequent in women with a 2:1 ratio. Sinus venosus atrial septal defect is usually associated with partial anomalous pulmonary venous drainage from the right superior pulmonary vein to the right atrium directly or indirectly through the superior vena cava. Rarer still, is the inferior sinus venosus, which may be associated with partial anomalous venous drainage from the right inferior pulmonary vein. CASE REPORT: 13-year-old patient with a history of intervention for interatrial defect closure with Amplatzer occluder at the age of six. He was brought to receive medical attention for fatigue and dyspnea that had been progressing for 2 years. Cardiac CT reported partial anomalous connection of pulmonary veins and echocardiogram reported a residual atrial septal defect of 10 mm and mild to moderate pulmonary hypertension. Based on the findings, surgical treatment was decided. EVOLUTION: In correction surgery, we observed Amplatzer occluder incorrectly positioned, the device was removed and flow was redirected from right pulmonary veins to left atrium with bovine pericardium patch. After the surgical intervention, the patient had a favorable evolution without no post-surgical complications. At follow-up, 15 days after medical discharge, the patient was asymptomatic, and a cardiac CT scan showed the corrected interatrial defect. CONCLUSION: The treatment of atrial septal defect should be individualized, since it will depend on the size of the defect, the age at the time of diagnosis, the magnitude of the shunt, the severity of the symptoms and the presence of other conditions. If the defect requires repair, it is important to weigh the benefits of choosing percutaneous closure vs. surgical intervention to avoid the need for reintervention, as in the present case. Closure and redirection of pulmonary vein flow with bovine patch is a safe and effective option.

Vortex evolution and merging mechanism across 180° sharp bend for laminar inflow

The present study deals with the fundamentals of vortex evolution and merging across a 180° sharp bend for laminar inflow (Re = 800). A three-dimensional flow and pressure distribution across the bend are analyzed by using particle image velocimetry measurements. The results show that the sudden flow redirection and adverse pressure gradient create a recirculation region in the vicinity of the divider wall. The vorticity and turbulent kinetic energy distribution highlight the presence of a shear layer between the recirculation and mainstream turning flow. A Rayleigh instability analysis shows the existence of centrifugal instabilities outside the shear layer in the mainstream turning flow. The imbalance of centrifugal and pressure forces act in unison to produce a net force that creates Dean instability across the mainstream turning flow. Consequently, two pairs of counter-rotating Dean vortices develop after the first turn, possibly merging into a single pair after the subsequent 90° turn. Finally, the evolution and merging of Dean vortices are explained with the help of a conceptual diagram illustrating the force interaction and the formation of counter-rotating currents.

Influences of deposition upslope the barrier on the dynamic impact of dry granular flow

The destructive granular flow hazards can be mitigated by intercepting the solid particles using protective barrier in the flow paths. Changes in the performance of barrier are usually observed in this process due to deposition occurring behind the barrier. However, there is a limited understanding about the effect of deposition on the dynamic impact of subsequent flows due to a complex process that involves the flow redirection and deposition entrainment by subsequent incoming flow. We investigate the dynamics of flow-barrier interaction by conducting flume tests with different deposition heights h0 normalized by barrier height H and flume inclination angles α. The impact of pileup flows and jet-like runup flows on barrier with deposition shows different flow features and barrier responses and is governed by the deposition height. An increasing normalized deposition height h0/H can mitigate barrier load and flow basal stress due to buffering effect of deposition by enhancing energy dissipation during impact. A depth-averaged analytical model is developed to estimate the changes in flow velocity and flow depth for different flow regimes (pileup/jet-like runup) impacting the barrier with deposition, considering the entrainment of deposition by incoming flow. Experimental results indicate that the proposed models are more reliable in estimating granular flow impact force compared to traditional analytical impact models that neglect the changes of flow velocity and flow depth by deposition.

Flow Diverter Treatment Using a Flow Re-Direction Endoluminal Device for Unruptured Intracranial Vertebral Artery Dissecting Aneurysm: Single-Center Case Series and Technical Considerations.

This study aimed to evaluate the effectiveness, safety, and technical considerations of flow diverter (FD) treatment using a Flow Re-direction Endoluminal Device (FRED) for unruptured intracranial vertebral artery dissecting aneurysms (VADAs). We conducted a retrospective study of 23 patients with unruptured intracranial VADAs who underwent FD treatment using a FRED between June 2017 and August 2021. Symptoms, imaging findings, treatment strategies, and angiographic and clinical outcomes were evaluated. Dissections were categorized according to the dominance of the VA in which they occurred: dominant VA, co-dominant VA, and non-dominant VA. All patients successfully underwent FD treatment with either a FRED (n=11) or FRED Jr. (n=12). Complete occlusion rates were 78.3% at 6-month follow-up magnetic resonance angiography and 91.3% at 12-month. There were no instances of complications, recurrence, or retreatment during a median follow-up of 20 months. Dissections occurred in the dominant VA in 3 cases (13.0%), the co-dominant VA in 13 cases (56.5%), and the non-dominant VA in 7 cases (30.4%). Intimal flap and true lumen stenosis were observed in 39.1% and 30.4% of cases, respectively. Four cases required a bilateral VA approach due to technical difficulties, all in the non-dominant VA. Flow diversion treatment using a FRED for unruptured intracranial VADAs proved feasible and safe, yielding satisfactory occlusion rates. Technical challenges were more likely in lesions involving non-dominant VAs in the acute or subacute stage, mainly due to associated intraluminal lesions compromising the arterial lumen.

Difference in the cumulative incidence of aneurysmal occlusion by Flow Re-direction Endoluminal Device and Pipeline Embolization Device in the treatment of unruptured internal carotid artery aneurysms: a propensity score-matched cohort study.

The introduction of flow diverters (FDs) has represented a paradigm shift in the management of unruptured cerebral aneurysms (UCA). Flow Re-direction Endoluminal Devices (FREDs) and Pipeline Embolization Devices (PEDs) have gained widespread popularity. We aimed to investigate the cumulative incidence of aneurysm occlusion. A total of 195 patients with 199 UCAs were analyzed retrospectively. The outcomes were aneurysmal occlusion during the follow-up, a modified Rankin Scale score of 0-2 at 90days, additional treatment, major stroke, and steno-occlusive events of FD. Propensity score-matched analysis was performed, controlling for age, sex, aneurysmal size, and location of the internal carotid artery (ICA) aneurysm. Non-ICA aneurysms were excluded from matching. During the follow-up period (median, 366days), complete and satisfactory aneurysmal occlusions were observed in 128 (68%) and 148 (78%) of 189 UCAs in the unmatched cohort. The 142 (71 each) propensity score-matched cohort was complied. The FRED group had a higher cumulative incidence of ICA aneurysm occlusion (complete: HR 2.7, 95% CI 1.4-5.1, p = 0.0025; satisfactory: HR 2.4, 95% CI 1.1-5.2, p = 0.025). The proportion of additional treatment was significantly smaller in the FRED group (OR 0.077, 95% CI 0.010-0.57, p = 0.0007). Other outcomes showed no significant differences. Propensity score-matched analysis indicated that FRED might have a higher cumulative incidence of aneurysmal occlusion in the treatment of unruptured ICA aneurysms. Whether a cumulative incidence of aneurysmal occlusion may differ by the type of FDs warrants further investigation.

Usefulness of silent magnetic resonance angiography for intracranial aneurysms treated with a flow re-direction endoluminal device.

Flow re-direction endoluminal device (FRED) is a novel dual-layer flow-diverting stent to treat cerebral aneurysms with high obliteration rates, however, it induces inevitable metal-related artifacts. We compared silent magnetic resonance angiography (MRA), a new MRA method using ultra-short time of echo and arterial spin-labeling, with conventional time-of-flight (TOF)-MRA for imaging aneurysms treated using FRED. Between May 2020 and September 2022, 16 patients with unruptured internal carotid aneurysms treated using FRED simultaneously underwent silent MRA and TOF-MRA after treatment, with 36 follow-up sessions in total. Two observers independently graded the quality of intra-aneurysmal flow and stented parent arteries under both types of MRA from 1 (not visible) to 4 (nearly equal to digital subtraction angiography [DSA]), with reference to DSA images as a standard criterion. The mean scores for intra-aneurysmal flow and stented parent arteries were significantly better for silent MRA (3.93 ± 0.21 and 3.82 ± 0.32, respectively) than for TOF-MRA (2.08 ± 0.99 and 1.92 ± 0.79, respectively) (P < 0.01). Intermodality agreements for intra-aneurysmal flow and stented parent arteries were 0.87 and 0.90, respectively. Silent MRA is superior to TOF-MRA for assessing patients treated with FRED, with potential as an alternative imaging modality to DSA.

FRED Jr stent for acute flow diversion in ruptured cerebral aneurysms arising from small-caliber vessels: a clinical case series.

Treatment of ruptured aneurysms arising from small-caliber (< 2.5 mm) or distal vessels beyond the circle of Willis is considered challenging with all treatment modalities. Recently, the Flow Re-Direction Endoluminal Device Junior (FRED Jr) stent, designed for flow diversion in small arteries, was approved in the United States for the treatment of nonruptured aneurysms. Here, the authors report their experience using this device in the setting of subarachnoid hemorrhage (SAH). Clinical and radiological records of patients sustaining SAH treated with a FRED Jr stent between June 2020 and October 2022 were reviewed. Treatment course, including antiplatelet therapy, external ventricular drain (EVD) management, and vasospasm, and clinical outcomes were analyzed. Angiographic results were assessed according to the O'Kelly-Marotta (OKM) grading scale. Nine patients at a median age of 62 (range 27-75) years were included. The median Hunt and Hess grade was II (IQR I) and the median modified Fisher grade was 4 (IQR 1). Aneurysm morphology types included saccular (6 patients), blister (1 patient), and dissecting (2 patients), and the aneurysms were located at the anterior communicating artery complex (n = 3) at the A2/A3 (n = 3), M2/M3 (n = 1), V4 (n = 1), and P2 (n = 1) arterial segments. All stents were deployed successfully with no intraprocedural complications. Postoperatively, no rebleeding events were encountered. Vasospasm therapy was initiated in 6 patients, and no symptomatic EVD-related hematomas were observed. Postoperative ischemic events were encountered in 2 patients. The median 3-month modified Rankin Scale score was 2 (IQR 1) for the 7 surviving patients, and 3-month radiographic follow-up revealed OKM grade D in 4 of 7 patients. Flow diversion using the FRED Jr stent is feasible as a potential treatment strategy for acutely ruptured aneurysms arising from small-caliber vessels. The complication profile reported in this series is comparable to those of historical microsurgical cohorts, and effective protection was conferred by this treatment modality. Therefore, our small cohort provides a glimpse into a new tool for successfully achieving acute flow diversion for this subset of difficult-to-treat aneurysms.

Data–Driven Wake Steering Control for a Simulated Wind Farm Model

Abstract: Upstream wind turbines yaw to divert their wakes away from downstream turbines, increasing the power produced. Nevertheless, the majority of wake steering techniques rely on offline lookup tables that translate a set of parameters, including wind speed and direction, to yaw angles for each turbine in a farm. These charts assume that every turbine is working well, however they may not be very accurate if one or more turbines are not producing their rated power due to low wind speed, malfunctions, scheduled maintenance, or emergency maintenance. This study provides an intelligent wake steering technique that, when calculating yaw angles, responds to the actual operating conditions of the turbine. A neural network is trained live to determine yaw angles from operating conditions, including turbine status, using a hybrid model and a learning-based method, i.e. an active control. The proposed control solution does not need to solve optimization problems for each combination of the turbines’ non-optimal working conditions in a farm; instead, the integration of learning strategy in the control design enables the creation of an active control scheme, in contrast to purely model-based approaches that use lookup tables provided by the wind turbine manufacturer or generated offline. The suggested methodology does not necessitate a substantial amount of training samples, unlike purely learning-based approaches like model-free reinforcement learning. In actuality, by taking use of the model during back propagation, the suggested approach learns more from each sample. Based on the flow redirection and induction in the steady state code, results are reported for both normal (nominal) wake steering with all turbines operating as well as defective conditions. It is a free tool for optimizing wind farms that The National Renewable Energy Laboratory (USA) offers. These yaw angles are contrasted and checked with those discovered through the resolution of an optimization issue. Active wake steering is made possible by the suggested solution, which employs a hybrid model and learning-based methodology, through sample efficient training and quick online evaluation. Finally, a hardware-in-the-loop test-bed is taken into consideration for assessing and confirming the performance of the suggested solutions in a more practical setting.

396 North American Multicenter Experience of the Flow-Redirection Endoluminal Device (FRED) in the Treatment of Intracranial Aneurysms

INTRODUCTION: Flow-diverters have revolutionized the endovascular treatment of intracranial aneurysms. The evidence on the Flow Re-direction Endoluminal Device (FRED) is limited compared to some counterparts that have been available for clinical use longer. METHODS: Between June 2020 and November 2021, consecutive cerebral aneurysms treated using FRED were included across 7 North American centers. Data collected included patient demographics, aneurysm characteristics, peri-procedural and long-term complications, modified Rankin Scale (mRS) scores, and radiologic follow-up. RESULTS: 133 aneurysms in 116 patients treated in 123 FRED deployment procedures were included. One hundred twenty-six aneurysms (94.7%) were unruptured, 117 (88.0%) were saccular, and 123 (92.5%) aneurysms were located in the anterior circulation. Mean aneurysm maximal width and neck sizes were 7.2 mm and 4.1 mm, respectively. Successful FRED deployment was achieved in 122 (99.2%) procedures. Radiologic follow-up was available for 101 aneurysms at a median duration of 7.0 months. At the last follow-up, complete occlusion was observed in 55.4%, residual neck in 8.9%, and filling aneurysm in 35.6%. On multivariate regression analysis, age (OR = 0.93; p = 0.001) and aneurysm neck size (OR = 0.83; p = 0.048) negatively correlated with odds of complete occlusion. The retreatment rate was 6/124 (4.8%). The overall complication rate was 31/116 (26.7%). Parent vessel occlusion, covered branch occlusion, and in-stent stenosis were detected in 9/99 (9.1%), 6/63 (9.5%), and 15/99 (15.2%) of the cases, respectively. FRED-related, symptomatic, thromboembolic, and hemorrhagic complication rates were 22.4%, 12.9%, 6.9%, and 0.9% respectively. The morbidity rate was 10/116 (8.6%). CONCLUSIONS: As the first large-scale North American multi-center FRED experience, this study confirms FRED’s ease of successful deployment but suggests a lower efficacy and higher rate of complications compared to previous European and South American FRED studies and other flow diverting devices.

Evolution of eddy viscosity in the wake of a wind turbine

Abstract. The eddy viscosity hypothesis is a popular method in wind turbine wake modeling for estimating turbulent Reynolds stresses. We document the downstream evolution of eddy viscosity in the wake of a wind turbine from experimental and large-eddy-simulation data. Wake eddy viscosity is isolated from its surroundings by subtracting the inflow profile, and the driving forces are identified in each wake region. Eddy viscosity varies in response to changes in turbine geometry and nacelle misalignment with larger turbines generating stronger velocity gradients and shear stresses. We propose a model for eddy viscosity based on a Rayleigh distribution. Model parameters are obtained from scaling the eddy viscosity hypothesis and demonstrate satisfactory agreement with the reference data. The model is implemented in the curled wake formulation in the FLOw Redirection and Induction in Steady State (FLORIS) framework and assessed through comparisons with the previous formulation. Our approach produced more accurate flow field estimates with lower total error for the majority of cases.

Safety and efficacy of flow diverter stents in the treatment of middle cerebral artery aneurysms: a single-center experience and follow-up data

This study aims to evaluate the safety and efficacy of flow diverters (FDs) in the treatment of middle cerebral artery (MCA) aneurysms and share the follow-up (F/U) results. The treatment and F/U results of 76 MCA aneurysms treated with the flow re-direction endoluminal device (FRED), FRED Jr., and pipeline embolization device (PED) FD stents were evaluated retrospectively. The aneurysm occlusion rates were compared between FDs, and the integrated and jailed branches were evaluated through follow-ups. The oversizing of the stent was compared between occluded/non-occluded aneurysms and integrated branches. The mean F/U duration was 32 ± 6.3 months, and the mean aneurysm diameter was 4.45 mm. A total of 61 (80.3%) aneurysms were wide-necked; 73 (96.1%) were saccular; 52 (68.4%) were located at the M1 segment; and 36 (45.6%) FREDs, 23 (29.1%) FRED Jr.s, and 19 (24.1%) PEDs were used for treatment. The overall occlusion rates for the 6-, 12-, 24-, 36-, and 60-month digital subtraction angiographies were 43.8%, 63.5%, 73.3%, 85.7%, and 87.5% respectively. The last F/U occlusion rates were 67.6% for FRED, 66.7% for PED, and 60.6% for FRED Jr. (P = 0.863). An integrated branch was covered with an FD during the treatment of 63 (82.8%) aneurysms. A total of six (10%) of the integrated branches were occluded without any symptoms at the last F/U appointment. The median oversizing was 0.45 (0-1.30) for occluded aneurysms, and 0.50 (0-1.40) for non-occluded aneurysms (P = 0.323). The median oversizing was 0.70 (0.45-1.10) in occluded integrated branches and 0.50 (0-1.40) in non-occluded branches (P = 0.131). In-stent stenosis was seen in 22 (30.1%) of the stents at the 6-month F/U and in only 2 (4.7%) at the 24-month F/U. Thus, none of the patients had any neurological deficits because of the in-stent stenosis. Severe in-stent stenosis was seen in two stents. MCA aneurysms tend to be complex, with integrated branches and potentially wide necks. FD stents are safe and effective in the treatment of MCA aneurysms, and the patency of the side and jailed branches is preserved in most cases. Higher occlusion and lower in-stent stenosis rates are seen with longer F/U durations.

Abstract Number ‐ 85: Distal Anterior Choroidal Artery Fusiform Aneurysm Successfully Treated with Flow Diversion

Introduction Anterior choroidal artery (AChA) aneurysms account for 3–5% of intracranial aneurysms, and are often saccular, arising at or near the origin of the AChA, with distal lesions being exceedingly rare. Contrary to saccular aneurysms, fusiform aneurysms are associated with a higher risk of rebleeding and mortality due to their formidable anatomy requiring advanced techniques including bypass, stent‐assisted coiling, and, more recently, flow diversion. While flow diverters are becoming more popular, they are currently only approved forinternal carotid artery segment aneurysms. However, many institutions areexpanding their use to more distal and smaller caliber vessels. Herein we present a novel pathology of a dissecting distal AChA fusiform pseudoaneurysm with a small vessel caliber treated successfully with flow diversion. Methods Case presentation and surgical technique. Results We describe a 40‐year‐old woman with monoclonal gammopathy of unknown significance (MGUS), lichen sclerosis, and an unspecified connective tissue disease presenting with diffuse subarachnoid hemorrhage (SAH) (World Federation of Neurosurgical Societies 1; Hunt &amp; Hess scale 2; Modified Fisher Scale 3). A digital subtraction cerebral angiogram revealed a dissecting (5×3 mm) left AChA pseudoaneurysm, 4mm distal to the origin (Figure 1). Flow Redirection Endoluminal Device (FRED Jr, Microvention, CA) (2.5mm 8/13 working/total length) was deployed within the vessel proximal to the aneurysm, preceded by an infusion of 5mg of verapamil to facilitate stent placement (Figure 2). Post procedure, she remained neurologically intact and was discharged on dual antiplatelet therapy (aspirin/ticagrelor). Repeat cerebral angiogram at six months showed patent flow diversion device and no pseudoaneurysm remnant (Figure 3) with a nonfocal physical examination. Conclusions Flow diversion may be a successful, and safe, therapeutic intervention for challenging distal intracranial aneurysms with smaller caliber vessels.

Assessment of the flow-diverter efficacy for intracranial aneurysm treatment considering pre- and post-interventional hemodynamics

Endovascular treatment of intracranial aneurysms with flow diverters (FD) has become one of the most promising interventions. Due to its woven high-density structure they are particularly applicable for challenging lesions. Although several studies have already conducted realistic hemodynamic quantification of the FD efficacy, a comparison with morphologic post-interventional data is still missing. This study analyses the hemodynamics of ten intracranial aneurysm patients treated with a novel FD device. Based on pre- and post-interventional 3D digital subtraction angiography image data, patient-specific 3D models of both treatment states are generated applying open source threshold-based segmentation methods. Using a fast virtual stenting approach, the real stent positions available in the post-interventional data are virtually replicated and both treatment scenarios were characterized using image-based blood flow simulations. The results show FD-induced flow reductions at the ostium by a decrease in mean neck flow rate (51%), inflow concentration index (56%) and mean inflow velocity (53%). Intraluminal reductions in flow activity for time-averaged wall shear stress (47%) and kinetic energy (71%) are present as well. However, an intra-aneurysmal increase in flow pulsatility (16%) for the post-interventional cases can be observed. Patient-specific FD simulations demonstrate the desired flow redirection and activity reduction inside the aneurysm beneficial for thrombosis formation. Differences in the magnitude of hemodynamic reduction exist over the cardiac cycle which may be addressed in a clinical setting by anti-hypertensive treatment in selected cases.

Letter: Commentary: The Pennsylvania Postmarket Multicenter Experience With Flow Redirection Endoluminal Device.

To the Editor: We read with great interest the commentary by Restrepo et al1 discussing our Pennsylvania multicenter postmarket experience with the Flow Redirection Endoluminal Device (FRED) (MicroVention Inc).2 We thank the authors for their interest and the editor for the opportunity to respond. We agree with the authors regarding the multiple important points raised in their commentary. As stated, endoluminal flow diversion (FD) has revolutionized the treatment paradigm of intracranial aneurysms, eventually becoming the standard-of-care treatment for a wide range of lesions, starting from internal carotid artery aneurysms with continuous expansion of its “on-label” utility to multiple “off-label” indications including more distally located and nonsaccular morphologically complex aneurysms.3,4 Despite the initial paradigm-shifting results, improvement of the devices' safety, mostly in decreasing thromboembolic complications, which are the most feared complications of these devices continued to be underway.5,6 These refinements encompassed incessant technical modifications such as introducing new endoluminal devices, establishing intrasaccular flow divertors with the Woven EndoBridge (MicroVention Inc) being the prodigy of these devices,7,8 and surface modifications feature of the existing devices such as Pipeline Embolization Device (PED) (Medtronic) Shield and the FRED-X devices. While large multicenter experiences are currently lacking from the United States, it is worth noting that thromboembolic rates reported from 3 international multicenter studies using the PED Shield (6.4%,9 3.3%,10 2.5%11) were not different from earlier studies using prior PED versions (eg, Prospective Study on Embolization of Intracranial Aneurysms with the Pipeline Device 2.1%12 and IntrePED 3.3%13). Concurrently to the PED Shield, the FRED-X device features a similar nanopolymer surface modification aiming to reduce device thrombogenicity. However, clinical data remain pending to be seen whether there are significant differences in occlusion rates or device's safety profile compared with its predecessor. Multiple questions currently remain in the FD literature; these include the long-term efficacy of the different devices and whether there are any safety/efficacy differences between these devices. A recent systematic review reported a pooled 5-year complete occlusion rate of 96% with most of the literature studies using PED14; however, the analysis did not account for the different FD devices nor particular aneurysmal location, and further studies on this remain warranted. Moreover, limited data are currently known regarding which aneurysm type might be suited for each of those devices and head-to-head comparative performance data of the different devices in certain aneurysms location, for which prospective trials would be needed. Until then, it is likely that operators' technical preferences and personal experiences will continue to be the main impetus for device selection in aneurysms treatment. A recently published survey directed to the US neurointerventional community aimed to elicit common themes in their adoption of the newly introduced devices (ie, Surpass Evolve [Stryker Neurovascular] and FRED devices) to the US market. In this survey, PED was reported as the most common choice for giant aneurysms and ruptured cases (PED Shield in particular), whereas FRED Jr was commonly chosen for distal aneurysms with small parent vessel diameters and Surpass, the device of choice for aneurysms with large parent vessels.15 It has been argued before that the decrease in complications likely stemmed from the device's adequately implied learning curve over time as well as attention to dual antiplatelet therapy and platelet function testing,16 particularly in light of recent level I randomized evidence supporting regular platelet function testing and subsequent medications adjusting in clopidogrel nonresponders or hyporesponders.6 Nonetheless and concurrently to the continuous expansion of the neurointerventional armamentarium with new devices and technologies, a more nuanced approach will likely be needed to identify the most appropriate device with a patient-centered case-specific–based approach.

Treatment strategy for giant thrombosed aneurysm of the basilar artery with associated obstructive hydrocephalus.

There is no established adequate treatment for thrombosed aneurysm of the basilar artery with obstructive hydrocephalus. We conducted coil embolization and peritoneal shunting followed by placement of a stent expected to exert flow diversion (FD) effects to treat 2 patients with giant thrombosed aneurysms of the basilar artery with associated obstructive hydrocephalus, with good results. From April 2019 to March 2021, consecutive two cases of symptomatic hydrocephalus due to giant thrombosed aneurysms in the posterior cranial fossa at our hospital were treated. At first, coil embolization was performed to prevent aneurysm rupture. After coil embolization, ventriculoperitoneal shunting was performed. Finally, stent-assisted coil embolization was performed with flow re-direction endoluminal device (FRED) or low-profile visualized intraluminal support device (LVIS) stent. Both patients were discharged after recovering well, with no postoperative hemorrhagic or ischemic complications. Staged surgery using a FRED for flow diverter or an LVIS stent expected to have FD effects may offer an effective treatment option.

Can wind turbine farms increase settlement of particulate matters during dust events?

Dust event is one of the main environmental problems affecting several countries of the world, and the dust burden is a severe threat to human health, environment, and socio-economic activities. Nevertheless, controlling windblown dust is a major challenge that hitherto has not been effectively overcome. Wind turbines can extract a considerable amount of kinetic energy from wind, reduce wind speed, and increase turbulence in the following wake, but can wind turbine farms increase the settlement of particulate matter during dust events? To examine this question, this study develops a framework based on FLOw Redirection and Induction in Steady State that calculates essential parts of the flow and dust concentration fields in wind farms. Eight different layouts and three wind turbines have been simulated to find the best wind farm arrangement that yields maximum dust deposition. It is found that wind farms, depending on the layout, decrease the wind speed by 8%–14.5%. In the best scenario, wind farms increase PM2.5 deposition by 23.3% and PM10 deposition by 34.2% compared to no wind farm case. Therefore, this study suggests that using wind turbine farms as wind barriers, provided the surface itself is not erodible, can be an effective way to control windblown dust.

Flow Diverter Performance for the Treatment of Intracranial Aneurysms: An International Multicenter Comparative Study

Background Current evidence comparing flow diverters (FDs) for the treatment of intracranial aneurysms is limited to single‐arm head‐to‐head retrospective and prospective studies. Herein, we aimed to compare the efficacy and safety of four FDs for the treatment of intracranial aneurysms. Methods We performed a retrospective, multicenter international cohort study of adult patients treated with FDs (Pipeline embolization device, Surpass Streamline, Flow Redirection Endoluminal Device, and Silk) for intracranial aneurysms between 2015 and 2021. Efficacy was determined by aneurysm occlusion at final follow‐up. Safety was determined by ischemic/hemorrhagic events and mortality. Secondary safety was assessed by technical complications. A mixed‐effect multivariable ordinal and logistic regression were performed to evaluate variables that predicted the outcomes of interest. Results We included 235 patients with 274 aneurysms. Treatment was performed with either the Pipeline embolization device (92), Surpass Streamline (56), Flow Redirection Endoluminal Device (47), and Silk (40). Median age was 57 (47–65) years. Most patients were asymptomatic (76%), and 8% had previous rupture. Most aneurysms were saccular (85%) and anterior (94%). The Pipeline embolization device subgroup had the largest aneurysms (6 mm, P =0.005). Median follow‐up time was 9 (6–14) months. Final overall complete occlusion was 72% without significant differences between FDs ( P =0.5). Total ischemic (5%) and hemorrhagic (3%) events were also similar ( P =0.1 and P =0.06). One patient expired (0.4%, P =0.6). In multivariable analysis, device diameter predicted aneurysm persistence and ≥50% in‐stent stenosis predicted ischemic/hemorrhagic complications. Conclusions Our findings comparing 4commonly used FDs in a heterogeneous population with mainly small‐sized aneurysms confirmed a similar safety and efficacy profile between devices.

Monte-Carlo simulations based hub height optimization using FLORIS for two interacting onshore wind farms

This study focuses on finding the optimum hub height (i.e., tower height) distributions for two interacting on-shore wind farms that are located on relatively complex terrain. Different optimization scenarios are studied, which take into account both the wind farm power output and the relevant cost variations due to changing hub heights. Simulations are performed using the Flow Redirection and Induction in Steady State (FLORIS) framework, which is modified to represent significant variations in hub height levels due to elevation differences, hence partial wake interactions that are occurring as a consequence, are more realistically represented. Optimization is based on a systematic procedure that includes introducing definitions of overall evaluation criterion parameters for objective setting and generation of design of experiments tables and related data via FLORIS simulations to properly cover the design space. A Pareto analysis of generated data to find the most influential parameters is then performed, and response surfaces are generated to represent these variations, which are, in turn, used for Monte Carlo based simulations to determine the optimized hub height distributions. Overall, the optimized results show a reasonable increase can be achieved in wind farm power output levels, while total tower height levels (hence related cost levels) are either not changing or in some cases even getting reduced for the wind farms in consideration.

Abnormal foreshortening of a Flow Re-Direction Endoluminal Device caused by in-stent thrombosis immediately after deployment.

Thromboembolic complications are a concern in the treatment of cerebral aneurysms using a flow diverter. In this study, we report a case of abnormal foreshortening of a Flow Re-Direction Endoluminal Device (FRED) caused by in-stent thrombosis immediately after its deployment. A 72-year-old woman had a large cavernous carotid aneurysm, which caused ptosis and diplopia. FRED deployment was planned, and dual antiplatelet therapy was initiated 2 weeks before the procedure. Under systemic heparinization, FRED was deployed with local compaction over the aneurysm orifice. Cone-beam computed tomography subsequently revealed slightly poor wall apposition at the proximal side. While the balloon catheter was prepared for angioplasty, the stent became abnormally foreshortened, the proximal side slipped into the aneurysm, and the internal carotid artery became occluded. FRED was removed using a snare wire, and recanalization was obtained. The lumen of the removed FRED was filled with thrombus. The antiplatelet therapy was changed to triple regimen, and a Pipeline Flex embolization device was placed 1 month later. At that time, no thromboembolic complications were noted. It was considered that thrombotic occlusion was followed by foreshortening of FRED on the distal side because of antegrade blood flow. Multiple factors, such as increased mesh density by locally compacted stent deployment, slightly poor wall apposition, clopidogrel resistance, and the dual-layer structure of FRED, may have been involved in thrombus formation.

The revised FLORIDyn model: implementation of heterogeneous flow and the Gaussian wake

Abstract. In this paper, a new version of the FLOw Redirection and Induction Dynamics (FLORIDyn) model is presented. The new model uses the three-dimensional parametric Gaussian FLORIS model and can provide dynamic wind farm simulations at a low computational cost under heterogeneous and changing wind conditions. Both FLORIS and FLORIDyn are parametric models which can be used to simulate wind farms, evaluate controller performance and can serve as a control-oriented model. One central element in which they differ is in their representation of flow dynamics: FLORIS neglects these and provides a computationally very cheap approximation of the mean wind farm flow. FLORIDyn defines a framework which utilizes this low computational cost of FLORIS to simulate basic wake dynamics. This is achieved by creating so-called observation points (OPs) at each time step at the rotor plane which inherit the turbine state. In this work, we develop the initial FLORIDyn framework further considering multiple aspects. The underlying FLORIS wake model is replaced by a Gaussian wake model. The distribution and characteristics of the OPs are adapted to account for the new parametric model but also to take complex flow conditions into account. To achieve this, a mathematical approach is developed to combine the parametric model and the changing, heterogeneous world conditions and link them with each OP. We also present a computationally lightweight wind field model to allow for a simulation environment in which heterogeneous flow conditions are possible. FLORIDyn is compared to Simulator for Offshore Wind Farm Applications (SOWFA) simulations in three- and nine-turbine cases under static and changing environmental conditions. The results show a good agreement with the timing of the impact of upstream state changes on downstream turbines. They also show a good agreement in terms of how wakes are displaced by wind direction changes and when the resulting velocity deficit is experienced by downstream turbines. A good fit of the mean generated power is ensured by the underlying FLORIS model. In the three-turbine case, FLORIDyn simulates 4 s simulation time in 24.49 ms computational time. The resulting new FLORIDyn model proves to be a computationally attractive and capable tool for model-based dynamic wind farm control.