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Logo of interneuroInterventional Neuroradiology
 
Interv Neuroradiol. 2015 November; 21(1 Suppl): 341–363.
PMCID: PMC4757171

ICS Abstracts

Analysis of Relationship Between Stent Structure and Flow Stagnation Using Self-Organizing Maps for Realistic Aneurysm

HAnzai1, Y Yoshida2, K Shimoyama3, S Obayashi3 and M Ohta3

1FRIS, Tohoku University, Sendai, Miyagi, Japan

2Graduate School of Engineering, Tohoku University, Sendai, Miyagi, Japan

3IFS, Melbourne, Tohoku University, Sendai, Miyagi, Japan

Purpose: A lot of hemodynamic parameters have been introduced to evaluate flow reduction by stent, however, the relationship between stent geometry and each hemodynamic parameter is not clear enough. In this study, we applied Self-organizing Maps (SOM) to search the detailed relationship between stent strut and hemodynamic parameters (Kohonen, 1982).

Material and Methods: Two thousands of stent design candidates evaluated with three hemodynamic parameters and 49 stent geometry parameters were stored during the optimization process. By using SOM software, 2,000 design candidates were visualized into 52 2D-maps while preserving their own features in the original 52-dimensional design space. Each map was divided into 17 clusters to characterize stent design and flow reduction.

Results: By comparing each cluster, critical design for reduction effect of each hemodynamic parameter is suggested. Strut placement on the inflow area is important to reduce velocity, vorticity, and shear rate. In addition to the inflow area, strut on the outflow area is required to reduce shear rate near the aneurysm wall.

Conclusions: Self-organizing Maps can be an effective tool to find the detailed relationship between stent design and hemodynamic parameters.

Reference

1. Kohonen T. Self-Organized Formation of Topologically Correct Feature Maps. Biological Cybernetics 1982; 43: 59–69.

Cerebral Aneurysm as a Hemodynamic Stress-Regulated Inflammatory Disease

TAoki1

1Center for Innovation in Immunoregulation Technology and Therapeutics, Kyoto University Graduate School of Medicine, Kyoto, Japan

Cerebral aneurysm can cause a subarachnoid haemorrhage after rupture as a major cause of it. Given the poor outcome of subarachnoid haemorrhage (mortality of 50%) and absence of medical therapy for unruptured aneurysm to prevent progression/rupture, mechanisms underlying cerebral aneurysm formation/progression/rupture should be clarified. To address this issue, we have used animal model of cerebral aneurysm and revealed some important machinery regulating cerebral aneurysm formation and progression (Aoki et al., 2015, 2013, 2012, 2011, 2009, 2007). In brief, cerebral aneurysm is a long-lasting inflammatory disease in intracranial arteries. In this process, NF-κB activation to induce pro-inflammatory factors and macrophage infiltration is revealed as crucial steps. Importantly, hemodynamic force loaded on endothelial cells of intracranial arteries greatly affects macrophage infiltration and inflammation in lesions. In this talk, recent insight regarding molecular mechanisms regulating cerebral aneurysm will be discussed.

References

2. Aoki T. Inflammation mediates the pathogenesis of cerebral aneurysm and becomes therapeutic target. Neuroimmunology and Neuroinflammation 2015; 2(2): 86–92.
3. Aoki T, Fukuda M, Narumiya S. Chronic inflammation in intracranial aneurysm formation. Inflammation and Regeneration 2013; 33(5): 283–287.
4. Aoki T, Narumiya S. Prostaglandins and chronic inflammation. Trends in Pharmacological Sciences 2012; 33(6): 304–311. [PubMed]
5. Aoki T, Nishimura M, Matsuoka T, Yamamoto K, Furuyashiki T, Kataoka H, Kitaoka S, Ishibashi R, Ishibazawa A, Miyamoto S, Morishita R, Ando J, Hashimoto N, Nozaki K, Narumiya S. PGE2-EP2 signaling in endothelium is activated to hemodynamic stress and induces cerebral aneurysm through an amplifying loop via NF-κB. Br. J. Pharmacol. 2011; 163(6): 1237–1249. [PMC free article] [PubMed]
6. Aoki T, Kataoka H, Ishibashi R, Nozaki K, Hashimoto N. Impact of monocyte chemoattractant protein-1 deficiency on cerebral aneurysm formation. Stroke 2009; 40(3): 942–951. [PubMed]
7. Aoki T, Kataoka H, Shimamura M, Nakagami H, Wakayama K, Moriwaki T, Ishibashi R, Nozaki K, Morishita R, Hashimoto N. NF-κB is a key mediator of cerebral aneurysm formation. Circulation 2007; 116(24): 2830–2840. [PubMed]

Impact of the Flow-Diverter Deployment Strategy on Side Branch Endothelialization: Over- Versus Undersizing

PBerg1, C Iosif2,3, S Ponsonnard4, E Pedrolo-Silveira2, C Yardin3,5, G Janiga1 and C Mounayer2,3

1Department of Fluid Dynamics and Technical Flow, University of Magdeburg “Otto-von-Guericke”, Magdeburg, Germany

2Interventional Neuroradiology Department, Dupuytren University Hospital (CHU Limoges), Limoges, France

3Applied Medical Research Team (ERMA), University of Limoges, Limoges, France

4Anesthesiology Department, Dupuytren University Hospital (CHU Limoges), Limoges, France

5Department of Histology, Cytology, Cellular Biology and Cytogenetics, Mother and Child (HME) University Hospital, Limoges, France

Flow-diverting devices are promising treatment options for intracranial aneurysms, since they reduce the blood flow into the dilatation and induce a stabilizing thrombosis. A previous study in rabbits concluded the safe use of flow-diverters regarding side branch patency. However, this conclusion has recently been challenged by published clinical cases and jailed side branches might occlude leading to insufficient blood supply. Especially differences in the local stent strut compression may have a drastic influence on subsequent endothelialization.

To investigate the outcome of different treatment scenarios, over- and undersized stent deployments were realized experimentally as well as computationally. Two Pipeline Embolization Devices were placed in the common carotid artery of large white swine. DSA and PC-MRI measurements were acquired pre- and post-stenting and after three months. To evaluate the stent strut endothelialization and the corresponding ostium patency, the swine were sacrificed and scanning electron microscopy measurements were carried out. A more detailed analysis of the near-stent hemodynamics was enabled by a realistic virtual stenting in combination with highly resolved Computational Fluid Dynamics simulations using case-specific boundary conditions.

The oversizing resulted in an elongated stent deployment with more open stent pores, while for the undersized case a shorter deployment with more condensed pores was present. In consequence, the side branch of the first case remained patent after three months and the latter almost fully occluded. The virtual investigation confirmed the experimental findings by identifying differences between the individual velocities and stent shear stresses at the distal part of the ostia.

The choice of flow-diverting device and the subsequent deployment strategy strongly influences the patency of jailed side branches. Therefore, careful treatment planning is required to guarantee sufficient blood supply in the brain territories supplied by those branches.

The Aneurysm DataBase and AneuX Project

PBijlenga1,5, S Hirsch2,4,5, I Wanke3,4,5 and D Rüfenacht3,4,5

1Neurochirurgie, Département des Neurosciences Cliniques, Hôpitaux Universitaires de Genève, Geneva, Switzerland

2Dept. Life Sciences and Facility Management, Institute of Applied Simulation, ZHAW Wädenswil, Switzerland

3Neuroradiology, Klinik Hirslanden, Zurich, Switzerland

4Center of Applied Biotechnology and Molecular Medicine (www.cabmm.uzh.ch), University of Zurich, Switzerland

5AneurysmDataBase, SwissNeuroFoundation, Switzerland

The prevalence of intracranial aneurysms is estimated to be around 3% of the Western World population. The incidence of unruptured intracranial aneurysm diagnosis is increasing due to an easier access to head imaging in the context of trauma, headaches or ill defined spells. Most of patients diagnosed are younger than 65 years and the average age of the patient population is around 53 years.

Currently many factors need to be assessed as proposed by the PHASES score study and the UIATS consensus to optimally manage patients identified with an incidental aneurysm. Nevertheless the clinical usability and predictive value of both scores and other currently available tools have yet not been validated nor quantified.

The personalized estimation and balance of risks associated with the natural history or different treatment strategies is therefore difficult to judge and it lacks comparable quantitative measurements. Suboptimal management may severely impact on the patient future quality of life and healthcare costs.

The aim of the SwissNeuroFoundation is to develop and provide technologies and tools to create a global AneurysmDataBase to stratify intracranial aneurysms and quantify risk associated with different management strategies.

The database is currently populated with information provided by the former @neurIST Project.

The database supports collecting structured information about each patient’s clinical condition, it represents the anatomy of the cerebrovascular tree and aneurysm as well as contains a whole genome scan and aneurysm dome microscopic analysis.

With increasing number of cases registered and careful analysis of the data the team was able to publish quantitative observations regarding risk factors associated with rupture. The results of the latest analysis of the AneurysmDataBase will be reported.

The future perspective to reduce the number of factors to be analyzed and possibly increase the objectivity of the risk balancing, resides in the development of a strategy using aneurysm location and advanced aneurysm dome shape analysis as principal factors. The model of aneurysm wall stability estimation based on shape will be tested against the PHASES and UIATS scores using the AneurysmDataBase. The efforts are executed within the AneuX project, supported by SystemsX.ch.

Connecting Hemodynamics and Wall Inflammation in Cerebral Aneurysms

JRCebral1, AM Robertson2 and J Frösen3

1George Mason University, Fairfax, Virginia, USA

2University of Pittsburgh, Pittsburgh, Pennsylvania, USA

3Kuopio University Hospital, Kuopio, Finland

Purpose: The purpose of this study was to evaluate the possible association between intra-saccular hemodynamic characteristics and markers of wall inflammation in intracranial aneurysms.

Methods: A total of 20 cerebral aneurysms, which underwent surgical clipping, were studied. Patient-specific computational fluid dynamics (CFD) models were constructed from pre-surgical CTA images. Numerical simulations were carried out using pulsatile flows and a number of hemodynamic variables were computed to characterize the intra-saccular flow environment. After clipping the aneurysm, a tissue sample was resected from the dome and analyzed histologically with CD45 to search for evidence of wall inflammation. For analysis, the sample was divided in two different manners. First, aneurysms were classified into an “inflammation” group if the number of CD45+ cells was larger than the median of CD45+ cells in the entire sample of 20 aneurysms; otherwise they were classified as “no-inflammation”. Hemodynamic variables were then statistically compared between these two groups. Secondly, aneurysms were subdivided into three groups according to their mean wall shear stress (WSS): 1) “low WSS” if WSS < 0.5*median(WSS), 2) “high WSS” if WSS > 2*median(WSS), and 3) “mid WSS” otherwise. The numbers of CD45+ cells in each group were then statistically compared. All statistical comparisons were carried out using the Wilcoxon rank sum test and differences were considered statistically significant if p < 0.05 (95% confidence).

Results: It was found that aneurysms in the “inflammation” group had on average significantly larger mean wall shear stress (p = 0.018), shear rate (p = 0.015), vorticity (p = 0.018), and viscous dissipation (p = 0.015) than aneurysms in the “no-inflammation” group. Conversely, it was also found that aneurysms in the “high WSS” group had on average significantly larger numbers of CD45+ cells (p = 0.0046) than the “mid WSS” and “low WSS” groups. Interestingly, it was observed that aneurysms with stable flow patterns tended to have larger numbers of inflammatory cells (p = 0.040) than aneurysms with unstable flows.

Conclusion: Our preliminary results suggest that there is a connection between intra-aneurysmal flow characteristics and wall inflammation in cerebral aneurysms. In particular, inflamed walls seem to be associated with higher levels of wall shear stress.

How can Physicians Benefit From Hemodynamic Simulations? An Individualized Therapy Planning Approach for Intracranial Aneurysms

L Daróczy1, PBerg1, O Beuing2 and G Janiga1

1Department of Fluid Dynamics and Technical Flow, University of Magdeburg “Otto-von-Guericke”, Magdeburg, Germany

2Department of Neuroradiology, University Hospital Magdeburg, Magdeburg, Germany

Flow-diverting devices are promising options to treat intracranial aneurysms minimal-invasively. However, due to the high diversity of aneurysm shapes and locations as well as the risk of jailed side branches, therapy planning can become challenging for neuroradiologists and neurosurgeons. Therefore, physicians would benefit from a reliable assistance using hemodynamic simulations.

In this study, a new method is introduced that combines a realistic deployment of a virtual flow-diverting stent for a given aneurysm with three-dimensional Computational Fluid Dynamics simulations and in-house optimization algorithms. Arbitrary treatment scenarios with different local compressions can be considered in a fully automated simulation loop. To proof the concept and demonstrate the clinical usability of this approach, the workflow was applied to different patient-specific aneurysm cases (e.g., terminal or lateral aneurysm). The impact on the corresponding blood flow behaviour was evaluated qualitatively as well as quantitatively and the optimal configuration was identified for each case under given conditions.

The virtual evaluation of a giant aneurysm, which was actually treated using a commercial flow diverter, revealed the impact of the local stent compression. The blood flow reduction into the dilatation ranged from 24% to 33%. Additionally, wall shear stress distributions on the luminal surface show clear variations depending on the treatment scenario. For the terminal aneurysm located at a cerebral bifurcation the optimal stenting configuration was found that reduces the aneurysmal inflow. Simultaneously, sufficient blood supply of the jailed side branches is maintained decreasing the interventional risk.

The findings illustrate the variability of a flow diverter deployment. Depending on the target function of the fully-automatic optimization workflow, improved treatment options for intracranial aneurysms can be identified virtually. Hence, physicians can be supported during their individualized therapy planning at no risk for the patient.

Chopsticks Technique for the Recanalization of T Junction Occlusions—Cases Report

YFang1, W Wen1, Q Huang1, Y Zhang1 and J Liu1

1Changhai Hospital, Shanghai, China

Purpose: To report an approach using 2 stent-retrievers in combination for the recanalizing of T junction occlusions.

Materials and Methods: Three consecutive T junction occluded cases treated with this initiative technique were collected. Each was treated with following procedures directly or after failure of single stent retriever based thrombectomy. A rebar 18 micro-catheter loaded with a 6/30 Solitaire AB device was navigated to the middle cerebral artery through an 8 F guiding catheter. Another rebar 18 micro-catheter loaded with revive 4.5/22 was placed in the anterior cerebral artery through the same guiding catheter. Unsheathe the two stent retrievers in sequence and gently pull them back together into the guiding catheter with constant aspiration through the guiding catheter. All of the 3 cases were recanalized with one single pass of the whole system. Embolus was found to be clamped by two retrievers.

Summary of Cases: Chopsticks technique might an alternative for T junction occlusions, especially those failed to recanalize by single stent-retrievers and those whose chance of embolus migration was high.

Estimation of Recanalization for Cerebral Aneurysms after Coil Embolization by Computational Fluid Dynamics Analysis

SFujimura1, H Takao1,2, M Watanabe2, T Suzuki1, K Shinohara1, S Takayama1, T Suzuki2, C Dahmani2,3, H Mamori4, T Ishibashi2, M Yamamoto4 and Y Murayama2

1Graduate School of Mechanical Engineering, Tokyo University of Science, Katsushika-ku, Tokyo, Japan

2Department of Neurosurgery, The Jikei University School of Medicine, Minato-ku, Tokyo, Japan

3Siemens Japan K.K., Shinagawa-ku, Tokyo, Japan

4Department of Mechanical Engineering, Tokyo University of Science, Katsushika-ku, Tokyo, Japan

Purpose: Recurrence of aneurysms after coil embolization remains a serious problem. The risk assessment protocol for preventing recanalization has not been established, and mechanisms of that phenomenon are not understood clearly, either. In this study, we investigated the flow characteristics on aneurysms after endovascular embolization to clarify the mechanisms of recanalization and estimate recurrence using computational fluid dynamics (CFD).

Materials and Methods: 12 recanalized cases and 14 stable cases were identified with 3-dimentional digital subtraction angiography. We investigated the flow characteristics of the aneurysms before and after initial coil embolization. An original parameter called Force per VER (FpV) was defined. The FpV considers simultaneously morphological factors (the area of the aneurismal neck and the volume embolization ratio (VER)), and a hemodynamic one (the maximum pressure at the coil surface). It implies force per unit VER. ROC analysis was conducted to specify the suitable VER value for each aneurysm case. The cut off value, which distinguishes whether one aneurysm will be a recanalized or not in the future was obtained from the ROC curve.

Results: The FpV showed statistically significant difference between recanalized and stable cases (P = 0.01); the value of FpV in recanalized cases tended to be higher than that in stable cases (recanalized: FpV = 0.016, stable: FpV = 0.008). ROC analysis shows that the cut off value of the FpV is 0.007 from the ROC curve.

Conclusion: Both hemodynamic and morphological factors may play an important role in the recanalization of aneurysms. By establishing the most suitable VER for each case from the cut off value of the FpV, the pressure on coil surface and the aneurismal neck area, the recurrence of aneurysms may be able to be prevented more effectively.

Flow Competition as a Factor of Patency or Occlusion of Side Branches After Flow Diverting Stent Placement in Intracranial Arteries: From Animal Translational Research to CFD Simulation and to Clinical Practice

CIosif1,2, P Berg3, S Ponsonnard4, P Carles5, G Trolliard5, E Pedrolo-Silveira1, G Mendes1, S Saleme1, C Yardin2,6 and C Mounayer1,2

1Interventional Neuroradiology Department, Dupuytren University Hospital (CHU Limoges), F-87000 Limoges, France

2Applied Medical Research Team (ERMA), University of Limoges, F-87000 Limoges, France

3Laboratory of Fluid Dynamics and Technical Flows, University of Magdeburg “Otto von Guerike”, Magdeburg, Germany

4Anesthesiology Department, Dupuytren University Hospital (CHU Limoges), F-87000 Limoges, France

5Science of Ceramic Processes and Surface Treatments, CNRS, UMR 7315, European Ceramic Center, University of Limoges, France

6Department of Histology, Cytology, Cellular Biology and Cytogenetics, Mother and Child (HME) University Hospital, F-87000 Limoges, France

Purpose: Jailing arterial branches emerging from the vicinity of intracranial aneurysms during flow diverting stent deployment has recently raised concerns. Even though initial animal studies showed patency of jailed branches (Kallmes, Ding et al., 2007, Darsaut, Bing et al., 2012), recent clinical data challenge their conclusions (Brinjikji, Murad et al., 2013). Clinical observations (Brinjikji, Lanzino et al., 2014, Saleme, Iosif et al., 2014, Iosif, Camilleri et al., 2015) suggest that the type of vascularization of the covered branch has an important role in its patency.

Materials and Method: We report the results of a translational animal research aiming to investigate the role of flow competition as a factor contributing in jailed branch patency. Fourteen large White swine were blindly allocated in two groups, modified by endovascular means to correspond to the anastomotic and terminal type of arterial circulation at the level of the ascending pharyngeal arteries (APhAs). Endovascular deployment of flow diverter in the right APhA bifurcations followed. Blood flow rates and velocities were quantified by 4D phase contrast MRA before and after stenting. Computational fluid dynamic simulations were generated. After three months the jailed ostia were evaluated by Scanning Electron Microscopy (SEM).

Results: Statistically significant correlation was found between flow rates post-stenting and group allocation. Circulating ostia surfaces, quantified by SEM, showed statistically significant difference between the two groups. Jailing an artery by a flow diverting stent, in the presence of flow competition, results in immediate flow rate reduction, with subsequent significant ostium endothelization. In the absence of flow competition, flow rates and maximal velocities are preserved post stenting and ostia remain patent.

Conclusion: These results find their application in therapeutic decision-making. We adjunctively discuss a single-center case series of patients harboring distal, bifurcation, intracranial aneurysms and how the flow competition concept influenced the decision-making process and the therapeutic outcome.

References

8. Brinjikji W, Lanzino G, Cloft HJ, Kallmes DF. Patency of the posterior communicating artery after flow diversion treatment of internal carotid artery aneurysms. Clin Neurol Neurosurg 2014; 120: 84–88. [PubMed]
9. Brinjikji W, Murad MH, Lanzino G, Cloft HJ, Kallmes DF. Endovascular treatment of intracranial aneurysms with flow diverters: a meta-analysis. Stroke 2013; 44(2): 442–447. [PubMed]
10. Darsaut TE, Bing F, Salazkin I, Gevry G, Raymond J. Flow diverters can occlude aneurysms and preserve arterial branches: a new experimental model. AJNR Am J Neuroradiol 2012; 33(10): 2004–2009. [PubMed]
11. Iosif C, Camilleri Y, Saleme, S, Caire, F, Yardin, C, Ponomarjova, S, Boncoeur-Martel, MP and Mounayer C. Diffusion-weighted imaging-detected ischemic lesions associated with flow-diverting stents in intracranial aneurysms: safety, potential mechanisms, clinical outcome, and concerns. J Neurosurg 2015; 1–10. [PubMed]
12. Kallmes DF, Ding YH, Dai D, Kadirvel R, Lewis DA, Cloft HJ. A new endoluminal, flow-disrupting device for treatment of saccular aneurysms. Stroke 2007; 38(8): 2346–2352. [PubMed]
13. Saleme S, Iosif C, Ponomarjova S, Mendes G, Camilleri Y, Caire F, Boncoeur MP, Mounayer C. Flow-diverting stents for intracranial bifurcation aneurysm treatment. Neurosurgery 2014; 75(6): 623–631. quiz 631. [PubMed]

Hemodynamic Differences of the Same Location Aneurysms According to the Rupture Status

FIshida1, M Tsuji2, S Masato1, T Sano2, T Hiroshi1, U Yasuyuki2, S Shinichi1 and S Hidenori2

1Department of Neurosurgery, Mie Chuo Medical Center, Tsu, Mie, Japan

2Department of Neurosurgery, Mie University Graduate School of Medicine, Tsu, Mie, Japan

Purpose: Hemodynamics characterizes the rupture status of cerebral aneurysms using computational fluid dynamics (CFD). However, aneurysm location and subarachnoid hemorrhage (SAH) would affect the quantitative hemodynamic metrics. Therefore, we investigated the hemodynamic parameters in two patients with SAH and multiple aneurysms at the same location.

Methods: 3D-CT angiography revealed ruptured and unruptured cerebral aneurysms in the same parent artery. Eleven morphological parameters and seven hemodynamic parameters were evaluated to diagnose the rupture status, and then the ruptured aneurysms were confirmed during the surgical clipping.

Results: Morphological examination revealed the higher maximum size and aspect ratio in both ruptured aneurysms compared with unruptured aneurysms. Lower wall shear stress (WSS), WSS gradient and aneurysm formation indicator were observed in both ruptured aneurysms. In contrast, the ruptured aneurysms had higher oscillatory shear index and oscillatory velocity index which was the novel hemodynamic parameter to quantify the fluctuation of flow velocity vector to detect complex flow pattern in 3D fluid domain.

Conclusion: Quantitative characterization of hemodynamic environment could identify the ruptured aneurysm without the bias of SAH and aneurysm location. Our results indicated that not only higher OSI but also 3D complex flow pattern in the fluid domain would be useful to discriminate the aneurysm rupture status.

References

14. David DN, et al. Pulsatile flow and atherosclerosis in the human carotid bifurcation. Positive correlation between plaque location and low oscillating shear stress. Arterioscler Thromb Vasc Biol 1985; 5: 293–302. [PubMed]
15. Jianping X, et al. Hemodynamic-morphological Discriminants for intracranial aneurysm rupture. Stroke 2011; 42: 144–155. [PMC free article] [PubMed]
16. Jou LD, et al. Wall shear stress on ruptured and unruptured intracranial aneurysms at the internal carotid artery. AJNR Am J Neuroradiol 2008; 29: 1761–1767. [PubMed]
17. Lu G, et al. Influence of hemodynamic factors on rupture of intracranial aneurysm: Mirror aneurysms model computational fluid dynamics simulation. AJNR Am J Neuroradiol 2011; 32: 1255–1261. [PubMed]
18. Mantha A, et al. Hemodynamics in a cerebral artery before and after formation of an aneurysm. AJNR Am J Neuroradiol 2006; 27: 1113–1118. [PubMed]
19. Murray CJ. The physical principle of minimum work applied to the angle of branching of arteries. J Gen Physiol 1926; 9: 835–841. [PMC free article] [PubMed]
20. Yoichi M, et al. Low wall shear stress is independently associated with the rupture status of middle cerebral artery aneurysm. Stroke 2013; 44: 519–521. [PubMed]
21. Yuji S, et al. Can temporal fluctuation in spatial wall shear stress gradient initiate a cerebral aneurysm? A proposed novel hemodynamic index, the gradient oscillatory number (GON). J Biomech 2009; 42: 550–554. [PubMed]

In Vitro Investigation of Contrast Flow Jet Timing after Flow Diversion in Patient-Specific Intracranial Aneurysms

LJou1 and G Chitalapani2

1Houston Methodist Hospital, Houston, Texas, U.S.A.

2Siemens Healthcare, Houston, Texas, U.S.A.

Purpose: After deployment of a flow diverter, visible changes of intra-aneurysmal flow can be observed on angiograms. This hemodynamic change is a critical mechanism for thrombosis and a fundamental basis of contrast stasis. However, these changes may not be consistent and vary by how the contrast is administrated. Our study investigates the factors that may control the appearance of intra-aneurysmal flow.

Materials and Methods: Three patient-specific aneurysm models between 11 and 25 mm were manufactured and each was implanted with a flow diverter. X-ray angiographic experiments of these models were performed at injection rates of Omniopaque between 0.2 and 2 ml/s. The timings of intra-aneurysmal flow jets were quantified.

Results: Significant changes of flow pattern are observed after placement of a flow diverter. At higher contrast injection rates, contrast influxes arrive at the aneurysm faster than those for slower injection rates. The flow patterns associated with slower injection rates exhibit strong inertia and correspond to the systole flow. Flow jets arrive at both the ICA and MCA aneurysms at the peak systole when the contrast is injected at 0.2 ml/s.

Conclusion: Visualization of intra-aneurysmal flow jet at the acceleration phase of the systole is possible by controlling the contrast injection rate. The systolic flows for both the ICA and MCA aneurysms can be visualized with low injection rates (<0.5 ml/s), while the diastolic flow jets can be appreciated better with an injection rate between 1 and 1.5 ml/s for the ICA aneurysms.

Hemodynamic Study of Stent Effects on Cerebral Aneurysm Models Using Scanning Stereoscopic Particle Image Velocimetry

KKamiya1, H Takao1,3, S Tateshima4, S Asakura1, C Ichikawa1, T Suzuki1, Y Kameya2, Y Murayama3, G Duckwiler4, F Vinuela4 and M Motosuke2

1Graduate school of Mechanical Engineering, Tokyo University of Science, Japan

2Department of Mechanical Engineering, Tokyo University of Science, Japan

3Departmenr of Neurosurgery, Jikei University School of Medicine, Japan

4Division of Interventional Neuroradiology, Department of Radiological Sciences, Ronald

Reagan UCLA Medical Center and David Geffen School of Medicine at UCLA

Purpose: Flow diverter (FD) stents are new devices for cerebral aneurysm treatment. According to past treatment results, over 70% of aneurysms were successfully occluded by FD treatment. However, some complications (e.g. headache and rupture) have been reported. Generally, hemodynamics change after treatment was considered to play an important role in these complications, but details are unclear. This study aims to reveal the effects of FD treatment on hemodynamics.

Methods: A flow measurement was conducted for four patient-specific aneurysm models. The silicone phantoms of these models were created based on digital subtraction angiography (DSA) images taken from three patients (i.e. one patient had two aneurysms). All the patients were treated with a FD. All aneurysms were side-wall type, one straight and the others - curved. For each aneurysm, pre- (without stent) and post- (with stent) operative models were prepared. Our original new FD stent (NS, porosity: 88%) was deployed into the parent artery part of the post-operative models. Scanning stereoscopic particle image velocimetry (SSPIV) was applied to obtain three-dimensional velocity fields in the models. Velocity root mean square (VRMS) and wall shear stress (WSS) were calculated from the measured velocity field. Inflow rate was calculated at the neck of the aneurysm. We compared these parameters between pre- (w/o stent) and post- (w/stent) operative models.

Results: For post-operative models, VRMS, inflow rate, and WSS decreased in all the cases.

Especially a large rate reduction was identified at the straight side-wall type model. The measurement results showed that treatment with NS promoted occlusion of aneurysm, i.e. preventing its rupture.

Conclusion: The current results showed that side-wall aneurysm treatment with NS, especially in the straight type, reduced VRMS, inflow rate and WSS.

Development of an Integrated 1D-0D Simulation System for Patient-Specific Cerebral Circulation

MKobayashi1, A Harada1, H Zhang2, S Yamada3 and M Oshima1,2

1Interfaculty Initiative in Information Studies, The University of Tokyo, Tokyo, Japan

2Department of Mechanical Engineering, The University of Tokyo, Tokyo, Japan

3Department of Neurosurgery, Stroke Center, Rakuwakai Otowa Hospital, Kyoto, Japan

In order to predict blood flow changes in the cerebral circulation resulted from carotid artery stenting, a patient-specific simulation can be a practical technique. Since the blood flow is altered by the surgical operation, it is necessary to include the effects of the entire circulatory system. A 1D-0D simulation can take account of them in a more practical manner comparing to a 3D-1D-0D simulation, and also can be performed with a patient-specific cerebral circulation which takes the entire cardiovascular system into account. The purpose of this study is to develop an integrated 1D-0D simulation system combined with multi-modal medical data such as MRI, CT and SPECT to obtain information of cerebral circulation for an individual patient.

The present integrated system consists of three processes: an image-based 3D geometric modeling,1 1D-0D simulation,2 and 3D visualization processes. The modeling system plays two roles: extraction of arterial geometries represented as the centerlines and quantification of patient's arterial geometries such as radii along the arterial centerlines for the 1D-0D simulation. In the simulation, the 1D simulation is performed in a part of the cerebral circulation uses the patient-specific geometry and flow information. The 3D visualization is developed so as to describe the results of the 1D-0D simulation such as flow rate, cross-sectional area in the region where the patient-specific data are used.

We have applied to medical images in pre- and post-operation of carotid artery stenting. The 1D-0D simulation process has been performed to use not only arterial geometric data but also flow data obtained from PC-MRI and SPECT. The 3D visualization showed that it became easy to understand flow distribution changes in Circle of Willis between pre- and post-operation.

References

22. Kobayashi M, Hoshina K, Yamamoto S, Nemoto Y, Akai T, Shigematsu K, Watanabe T and Ohshima M. Development of an Image-Based Modeling System to Investigate Evolutional Geometric Changes of a Stent Graft in an Abdominal Aortic Aneurysm. Circulation advpub, 2015. [PubMed]
23. Oshima M, Torii R, Tokuda S, Yamada S, Koizumi A. Patient-Specific Modeling and Multi-Scale Blood Simulation for Computational Hemodynamic Study on the Human Cerebrovascular System. Curr. Pharm. Biotechnol. 2012; 13: 2153–2165. [PubMed]

International Aneurysm CFD Challenge 2015 (Introduction Talk)

KKono1 and K Valen-Sendstad2

1Department of Neurosurgery, Showa University Fujigaoka Hospital, Kanagawa, Japan

2Biomedical Simulation Laboratory, Department of Mechanical & Industrial Engineering, University of Toronto, Toronto, ON, Canada

Purpose: Computational Fluid Dynamics (CFD) of intracranial flows has gained much interest over the past years and is arguably a useful tool for future clinical use. Drs. Steinman and Loth launched the “Aneurysm CFD Challenge 2012”, and concluded that pressure drop was reasonably well predicted among the vast majority of the participants (Steinman et al., 2012). Dr. Janiga followed up in 2013 and assessed whether CFD modellers could predict the ruptured aneurysm of two cases (Janiga et al., 2015). However, in both previous challenges, segmented surface geometries were provided along with other constraints, which may not reflect a normal collaboration between physicians and engineers

Materials and Methods: We have launched the Aneurysm CFD Challenge 2015 that is designed to mirror a “real-world” collaboration starting from Digital Imaging and Communication in Medicine (DICOM) data of five aneurysms. There are three questions we wish to answer in the current challenge: (i) what are the variabilities of image segmentation (ii) what are the differences in CFD results when surface and boundary conditions are not provided (iii) and is CFD really adding value with respect to rupture status prediction? The latter will be answered through providing clinicians the “normal” clinical data as clinicians’ challenge.

Results: Twenty-eight teams all over the world have participated in this challenge. We have obtained predictions from more than 200 clinicians. There are large variabilities of segmentations, CFD methods, and predictions. We have been analysing large data sets, and will open the results at the ICS.

Conclusion: This CFD challenge will uniquely reveal1 variabilities of segmentations and2 comparison of predictions of rupture status between CFD teams and clinicians. This challenge will be presented in two sessions: introduction talk by an organizer, and a workshop session with talks by an organizer and a few participants.

References

24. Steinman DA, et al. Variability of computational fluid dynamics solutions for pressure and flow in a giant aneurysm: the ASME 2012 Summer Bioengineering Conference CFD Challenge. J Biomech Eng. 2013; 135: 021016. [PubMed]
25. Janiga G, et al. The Computational Fluid Dynamics Rupture Challenge 2013—Phase I: prediction of rupture status in intracranial aneurysms. AJNR Am J Neuroradiol. 2015; 36: 530–536. [PubMed]

Uncertainty and Its Effects on Design of Coronary Stents

QLi1, S Tammareddi1, GY Sun1 and D Zheng1

1School of Aerospace, Mechanical and Mechatronic Engineering; The University of Sydney; New South Wales 2006, Australia

Purpose: Coronary stents are used widely as a minimally invasive device for unblocking occluded coronary arteries. Restenosis is the re-occlusion of the artery post stent implantation, largely caused by an injury to the artery during stent deployment (Lim et al., 2008), which necessitates careful design of stent to minimize such adverse effects. There are two critical issues involved in the design of stent structures. First, the risk of arterial injury should be minimized by imposing multiple design objectives, which can for example include reduction in dog-boning, foreshortening, elastic radial recoil, and stresses developed in the arterial wall during stent deployment (Li et al., 2009). Some of these objectives could compete with each other (Lim et al., 2008). Second, the stent insertion and deployment process is subject to uncertainties (noise) such as slight movement of the stent on balloon catheter, and changes in stent material properties during manufacturing and patient specific arterial size and properties. These critical issues place significant challenge in design optimization.

Materials and Methods: The nonlinear finite element analyses of a parameterized stent model are first conducted in a series of different models. The surrogate models are then constructed which formulate the mathematical relationship between stent geometrical parameters (control parameters) and the objective functions. The surrogate models include both mean and standard deviation responses. To address the issue of stent design involving uncertainties, a multiobjective robust optimization is adopted here (Sun et al., 2011, 2014 and Gu 2013) such that the effects of uncertainties on optimal objectives can be minimized. The Multiobjective Particle Swarm Optimization (MOPSO) algorithm is adopted for performing the robust optimization in this study.

Results: The different design objectives are found strongly competing with each other and thus the Pareto fronts are plotted to show the optimal set of trade-offs between the different objective functions. The uncertainties are of considerable effects on the optimisation results. The robust design minimised the effect of uncertainties by sacrificing some degree of multiobjective optimisation.

Conclusion: The design of coronary stents should take into account the multiple design objectives for addressing the clinical concerns. The design should also consider uncertainties whenever possible as they will largely affect the design and clinical outcomes.

References

26. Gu X, Sun G, Li G, Mao L, Li Q. A comparative study on multiobjective reliable and robust optimization for crashworthiness design of vehicle structure. Struct Multidisc Optim 2013; 48: 669–684.
27. Li N, Zhang H, Ouyang H. Shape optimization of coronary artery stent based on a parametric model. Finite Elements in Analysis and Design 2009; 45: 468–475.
28. Lim D, Cho S-K, Park W-P, Kristensson A, Ko J-Y, Al-Hassani S, Kim H-S. Suggestion of potential stent design parameters to reduce restenosis risk driven by foreshortening or dogboning due to non-uniform balloon-stent expansion. Annals of biomedical engineering 2008; 36: 1118–1129. [PubMed]
29. Sun G, Li G, Zhou S, Li H, Hou S, Li Q. Crashworthiness design of vehicle by using multiobjective robust optimization. Struct Multidisc Optim 2011; 44: 99–110.
30. Sun G, Song X, Baek S, Li Q. Robust optimization of foam-filled thin-walled structure based on sequential Kriging metamodel. Struct Multidisc Optim 2014; 49: 897–913.

Comparison Between CFD and MRI with 2D Velocity Vector Field and 3D Streamline in the Cerebral Aneurysm

YLi1, Y Yoneyama2, H Isoda2, T Kosugi3 and M Ohta1

1Tohoku University, Sendai, Miyagi, Japan

2Nagoya University, Nagoya, Aichi, Japan

3Renaissance of Technology Corporation, Japan

Purpose: Hemodynamic parameter could be obtained by many methods, like computational fluid dynamics (CFD) and magnetic resonance imaging (MRI) (Haruo, 2010). However, each method has its own merits and limitations. In order to achieve better understanding of the difference in each method, discussion of the results between different methods is necessary. This research shows the comparison between CFD and MRI with the same patient-specific geometry, with providing the 2D flow pattern, as well as 3D streamline.

Materials and Methods: A silicone phantom of the patient-specific aneurysm was manufactured. To decrease the geometrical difference between the silicone phantom and the 3D model in CFD, the silicone phantom was scanned by a Micro-CT scanner, and reconstructed to a 3D model. Working fluid used in MRI has similar property to human blood. Corresponding boundary conditions and fluid properties were set in CFD, to ensure that flow conditions are the same in each method.

Results: From the comparison between MRI and CFD, the shape of the edge of the geometry shows some discrepancies, as well as the flow pattern around the wall.

Conclusion: The low resolution in MRI may affect the measurement of geometry shape as well as the flow movement in the model, which need to be improved in future study.

Reference

31. Haruo Isoda, et al., Comparison of hemodynamics of intracranial aneurysm between MR fluid dynamics using 3D cine phase-contrast MRI and MR-based computational fluid dynamics. Neuroradiology 2010; 52. [PMC free article] [PubMed]

Association Between Flow-Rate Waveform-Based Flow Instabilities and Rupture Status Indicators in Cerebral Aneurysms: A CFD Study

HLiu1,2, L Xu1,2, A Saito3 and R Yamaguchi1

1Chiba University, 1–33, Yayoi-cho, Inage-ku, Chiba-shi, Chiba, Japan

2Shanghai Jiao Tong University and Chiba University International Cooperative Research Center, Chiba University, Chiba, Japan

3Aomori Prefectural Central Hospital, 2-1-1 Higashitsukurimichi, Aomori, Japan

CFD (computational fluid dynamics) has been proved to be of great potential but with challenge in cerebral aneurysm risk diagnosis. Recent studies report that flow instabilities appear to play an influential role in the evolution and rupture of aneurysms. However, how physiologically realistic inlet flow rate waveforms influence the flow instabilities and hence wall shear stress (WSS) fluctuations in aneurysms is still unclear. We used a CFD model of an anatomically realistic cerebral aneurysm to investigate the association between inlet waveform’s harmonic frequencies and flow fluctuations in the cerebral aneurysm. The three dimensional, unsteady Navier-Stokes equations were solved with the assumptions of rigid vessel walls and incompressible Newtonian fluid. The inlet waveform was given based on a one-dimensional (1D) model of the human cardiovascular system, and decomposed into Fourier series with a constant term and 8 harmonics. To identify the harmonic frequency dependence of the inlet waveform on flow instability mechanisms, we further performed power spectral density (PSD) analysis on the WSS fluctuations. Our simulated results demonstrated remarkable temporal and spatial WSS fluctuations in the aneurysm at late systolic when flow decelerates. There was an obvious relationship between the inlet waveform’s harmonic frequencies and the WSS fluctuations: the low-frequency harmonics in the inlet waveform caused pronounced WSS fluctuations corresponding with a maximal dominant frequency at 128 Hz but high-frequency harmonics seemed to influence less on flow instabilities in the cerebral aneurysm. There exists a harmonic frequency dependency in inlet flow rate waveforms associated with flow instabilities in cerebral aneurysms: low-frequency harmonics play a dominant role in causing significant WSS fluctuations. This is partly explained by that the low-frequency harmonics govern a primary adverse pressure gradient at late systole during flow deceleration, which induces transitional flow while giving it sufficient time to develop into flow instabilities whereas high-frequency harmonics do not but decay gradually.

References

32. Meng et al., High WSS or Low WSS? Complex interactions of hemodynamics with intracranial aneurysm initiation, growth, and rupture: Toward a unifying hypothesis. American Journal of Neuroradiology 2014; 1254–1262. [PubMed]
33. Poelma et al., Transitional flow in aneurysms and the computation of haemodynamic parameters. J R Soc Interface 2015; 12. [PMC free article] [PubMed]

High-Resolution Magnetic Resonance Vessel Wall Imaging (MR-VWI)

CMatouk1

1Neurosurgery & Diagnostic Radiology Section of Neurovascular Surgery, Yale University School of Medicine

High-resolution magnetic resonance vessel wall imaging (MR-VWI) is a newer imaging paradigm that is increasingly being used to characterize steno-occlusive diseases, for example, intracranial atherosclerosis and cerebral vasculitis. We reported for the first time thick vessel wall enhancement in 5 patients with ruptured intracranial aneurysms, and demonstrated its utility in determining the site-of-rupture in 3 patients harboring multiple aneurysms.1 More recently, Edjlali et al., reported that 16 of 17 ruptured aneurysms demonstrated circumferential wall enhancement.2 Nagahata et al., reported wall enhancement in 60 of 61 ruptured aneurysms.3 Taken together, these data establish a strong association between aneurysm wall enhancement and rupture status. Whether vessel wall enhancement is also a risk factor for future aneurysmal rupture is not known. However the recent demonstration by Edjlali et al., that circumferential wall enhancement was observed in unstable (and unruptured) aneurysms is certainly enticing.2

Herein, we describe our growing experience with MR-VWI in the evaluation of more than 100 intracranial aneurysms, 25 brain arteriovenous malformations (AVMs), and 3 cranial dural arteriovenous fistulas (DAVFs). We propose a new, unified hypothesis that spontaneously ruptured vascular structures demonstrate thick vessel wall enhancement and provide further evidence to support the contention that circumferential wall enhancement predicts future rupture.

References:

34. Matouk C, Mandell DM, Gunel M, Bulsara KR, Malhotra A, Hebert R, Johnson MH, Minja FJ. Vessel wall magnetic resonance imaging identifies the site of rupture in patients with multiple intracranial aneurysms: proof of principle. Neurosurgery 2013; 72(3): 492–6. [PubMed]
35. Edjlali M, Gentric JC, Regent-Rodriguez C, Trystram D, Hassen WB, Lion S, Nataf F, Raymond J, Wieben O, Turski P, Meder JF, Oppenheim C, Naggara O. Does aneurysmal wall enhancement on vessel wall MRI help to distinguish stable from unstable intracranial aneurysms? Stroke 2014; 45(12): 3704–6. [PubMed]
36. Nagahata S, Nagahata M, Obara M, Kondo R, Minagawa N, Sato S, Sato S, Mouri W, Saito S and Kayama T. Wall enhancement of the intracranial aneurysms revealed by magnetic resonance vessel wall imaging using 3D turbo spin-echo sequence with motion-sensitized driven-equilibrium: a sign of ruptured aneurysm? Clin Neuroradiol 2014; Oct 21 [Epub ahead of print]. [PubMed]

The Use of Computational Fluid Dynamics in the Diagnosis and Prognosis of the Cardiovascular Diseases (CVDs): An Update

YSMorsi1, SN Doost1, L Zhong2,3 and BY Su3

1Biomechanical and Tissue Engineering Lab, Faculty of Science, Engineering and Technology, Swinburne University of Technology, Victoria, Australia

2Duke-NUS Graduate Medical School, Singapore

3National Heart Research Institute of Singapore, National Heart Centre, Singapore

Purpose: The Cardiovascular Diseases (CVDs) are well known as the leading cause of the mortality and morbidity worldwide. Early diagnosis and prognosis of CVDs could effectively reduce these high mortality and morbidity rate. The recent developments of various innovative non-invasive diagnosis and prognosis tools to enhance our knowledge of cardiovascular physiological phenomena have been widely reported. In particular, the computational fluid dynamics (CFD) techniques have been effectively utilized in the analysis of cardiovascular hemodynamics, a key element in the initiation and propagation of the CVDs. However, despite the huge achievements of utilizing the CFD for analysing the cardiovascular fluid dynamic, the clinical implication of this technique has not yet well been accepted due to its limitations. This study set out to analysis the vortex formation and propagation in patient-specific left ventricle (LV) using the image-based CFD technique.

Methods: We implemented the cardiac images of patient-specific LV obtained using the Magnetic Resonance Imaging (MRI) in order to reconstruct the time-resolved 2D geometry of LV. All required image processing has been conducted using the freely available Segment software (http://segment.heiberg.se), and other steps include the geometry reconstruction, mesh generation, and CFD simulation has been conducted in the commercial solver ANSYS FLUENT.

Results: One of the more significant findings to emerge from this study was that an asymmetric and large vortex was generated beneath the aortic valve during the diastole that can enhance the ventricular pumping efficiency by redirecting the flow toward the aorta once systole phase starts. Moreover, the finding indicated that the blood flow pattern during the systole was considerably smooth and straightened toward the aortic valve.

Conclusion: The findings indicate that our proposed semi-automated IB-CFD to simulate the intraventricular blood flow dynamic over the whole cardiac cycle can provide insights to enhance our understanding of patient-specific intraventricular vortex formation and propagation.

The Parent Artery Configuration can Induce Flow Pattern and its Stent Pattern?

TNakayama1 and M Ohta2

1National Institute of Technology, Tsuruoka College, Tsuruoka, Yamagata, Japan

2Tohoku University, Sendai, Miyagi, Japan

Background and Purpose: In recently, the relationship between aneurysm and blood flow is discussed to be a classification for effective stent replacement. The role of stent is to reduce the blood flow speed in cerebral aneurysm. Previously, we found that there may be two types of flow pattern in the inflow of aneurysm and have developed the optimization of stent strut pattern using computational fluid dynamics (CFD) system. In this study, we investigated effect of stent strut pattern to the flow pattern in aneurysm neck.

Materials and Methods:

  • The blood vessel shape
    1. Patient-specific parent artery shape with a cerebral aneurysm was reconstructed using OsiriX from medical treatment images.
    2. The center line of patient-specific parent artery shape was extracted using a vascular modeling tool kit.
    3. The parent artery shape was reconstructed based on this center line using computer aided design (CAD).
  • The aneurysm shape

The shape was a combination of a straight pipe and a half sphere, and the aspect ratio (AR) value was fixed at 1.0.

  • Stent

The three stents based on z-type stent shape were implanted on the neck of the aneurysm.

  • CFD analysis

The constructed parent vessel, aneurysm, stent shape data were merged on computer, CFD analysis was performed by the comitial code (Ansys 15.0, Ansys Inc.).

Results and Conclusion: After stent implantation, the maximum WSS was increased in only one case and was decreased in the other cases. The maximum blood flow speed was increased in some case, and was decreased in the other cases. Although we found the classification of inflow and the stent with average WSS and speed, we still need to investigate the relationship the maximum WSS and the maximum blood flow speed.

Reference

37. Nakayama T, Sugiyama S and Ohta M. ‘Classification of Blood Flow in Cerebral Aneurysm Considering the Parent Artery’, ASME 2013 International Mechanical Engineering Congress and Exposition 2013; pp.V03AT03A033(7 pages).

In-Vitro Model with Flow for Surface Treatment for Endothelialization

MOhta1, S Matsumoto1, T Watanabe1, XB Han1 and H Kobayashi2

1Tohoku University, Sendai, Japan

2NIMS, Tsukuba, Japan

Purpose: Quick endothelialization on and around stent wire is important for suppression of restenosis after stent placement for stenosis. In previous research, it was described that endothelial cells suppress the intimal hyperplasia leading to restenosis and promote antithrombogenicity of stent. It is expected that immobilization of Type I collagen which has cell adhesiveness on stent wire will promote endothelialization on wire, so this study examined the influence of collagen immobilization by HMDI on endothelialization on and around wire with shear stress (WSS) environment.

In this study, at first, observation methods for endothelialization on were examined. Next, endothelialization on bare wire and collagen immobilized wire under no flow and with WSS environment examined.

Materials and Methods: A circuit was connected in a flow exposure system called flow chamber consisted of roller pump, pulse damper and reservoir. And, Medium 199 added 20% FBS and penicillin (Proliferative Medium, PM) was circulated with 170 ml/min flow rate which made 2 Pa Wall Shear Stress (WSS) on the bottom of flow circuit before implanting wire, for 24 hours. Before wire placement, the flow circuit's height is 0.6 mm and width is 1.8 mm as a rectangle and the flow is run along the width. Then a flat WSS of 2 Pa is distributed in the circuit.

Results: More endothelial cells (ECs) attached on collagen immobilized wire than on bare wire. This result is similar result to the chamber without flow. However, the cells in upstream on bare wire is higher density than that in downstream whereas the cells on collagen wire is the same. This result is a specific result in the flow condition. These results suggest that the flow condition is important factor when the pre-clinical (or pre-animal) test is established. And collagen immobilization will promote endothelialization on wire. In addition, around the wire, increase of EC density occurred in the area with WSS gradient(WSSG), and this result suggested that WSS occurred by placement of wire will affect endothelialization around wire.

Conclusion: The flow chamber we developed can be used for the first trial before a clinical or animal test to check the endothelialization of wire and around the wire. Collagen treatment may be a good method for endothelialization.

References

38. Kobayashi H, et al. Biomaterials. Covalent immobilization of proteins on to the surface of poly (vinyl alcohol) hydrogel 1991; 12(8): 747. [PubMed]
39. Matsumoto S. et al., Influence of Ni-Ti Wire under the Shear Stress Environment on Endothelialization, Proc. 10th ICFD. 2013; 602.

Patient-Specific Modelling of Leukocyte Transport in Cerebral Aneurysms

COu1, J Wang1, W Huang1, JCK Kwok2,3, GKC Wong4 and MMF Yuen1

1Department of Mechanical and Aerospace Engineering, Hong Kong University of Science and Technology, Kowloon, Hong Kong

2Division of Biomedical Engineering, Hong Kong University of Science and Technology, Kowloon, Hong Kong

3Department of Neurosurgery, Kwong Wah Hospital, Kowloon, Hong Kong

4Division of Neurosurgery, Prince of Wales Hospital, The Chinese University of Hong Kong, New Territories, Hong Kong

Purpose: Inflammation plays a key role in the initiation, progression and rupture of aneurysms (Chalouhi et al., 2012), but is difficult to be monitored in patients. Our objective was to demonstrate that computational fluid dynamics (CFD) combined with digital subtraction angiogram (DSA) could be used to study leukocyte transport phenomenon inside cerebral aneurysms in a patient-specific manner.

Methods: A 63-year-old woman presented with symptoms due to a giant unruptured ophthalmic internal carotid artery (ICA) aneurysm, while a 47-year-old woman due to a small unruptured left cavernous segment ICA aneurysm. The 3D models of both aneurysms were reconstructed from DSA images. CFD simulations were performed on these models where blood was modelled as multiphase flow with particles of erythrocytes and leukocytes (Jung, 2006).

Results: The difference of leukocyte distributions between these two aneurysms was significant. Though the average concentrations of leukocytes in both cases were about the same level, the elevated level of leukocyte concentration was observed in some small regions on the giant aneurysmal wall, where may have inflammation and bear a high risk of rupture (Frosen, 2004).

Conclusion: We demonstrated the feasibility to study leukocyte transport phenomenon inside cerebral aneurysms by an image-based patient-specific CFD analysis. More studies are needed before it applies for evaluating aneurysm rupture risk in clinical applications.

References

40. Chalouhi N, Ali MS, Jabbour PM, Tjoumakaris SI, Gonzalez LF, Rosenwasser RH, Koch WJ, Dumont AS. Biology of intracranial aneurysms: Role of inflammation. J Cereb Blood Flow Metab. 2012; 32: 1659–1676. [PMC free article] [PubMed]
41. Frösen J, Piippo A, Paetau A, Kangasniemi M, Niemelä M, Hernesniemi J, et al. Remodeling of saccular cerebral artery aneurysm wall is associated with rupture: histological analysis of 24 unruptured and 42 ruptured cases. Stroke. 2004; 35: 2287–2293. [PubMed]
42. Jung J, Hassanein A, Lyczkowski RW. Hemodynamic computation using multiphase flow dynamics in a right coronary artery. Annals of Biomedical Engineering 2006; 34: 393–407. [PubMed]

Y-Configured, Dual Stent-Assisted Coiling of 12 Basilar Apex Aneurysms

JPiao1, L Qi1, C Xuan1 and Y Zhongxi1

1Department of Neurosurgery, First Hospital of Jilin University, Changchun, Jilin, China PR

Purpose: Due to the special and complex anatomical features of the basilar apex aneurysm, the methods of the endovascular treatments are diverse. Y-configured, dual stent-assisted coiling is one of the favourite treatments nowadays. To research such kind of endovascular treatment is necessary.

Methods: We retrospectively reviewed 12 basilar apex aneurysms treated with Y-configured, dual stent-assisted coiling during 1st January, 2014 to 31st March, 2015 in our hospital. 10 of 12 aneurysms were in the acute phase of subarachnoid hemorrhage. Another 2 cases were unruptured aneurysms without any clinical symptoms. All of endovascular treatments were performed under general anesthesia. In hybrid stenting, a NEUROFORM stent and a SOLITAIRE stent were successfully placed and implanted in proper order before coiling. All of coil embolization were accomplished successfully. 9 of 12 cases were followed up by DSA from 3 months to 9 months.

Results: 11 of 12 cases had excellent clinical outcomes. Neurologic disorder appeared 2 days after treatment in remaining 1 case, whose clinical symptom performed blurry vision. After 10 days’ positive pharmacotherapy, the clinical symptom was recovered well. Follow-up DSA examinations showed stable and total occlusion of all coiled aneurysms.

Conclusion: The results of this retrospective analysis show that Y-configured, dual stent- assisted coiling of apex aneurysm can achieve good clinical outcome. But much longer term follow-up is advocated to assess the prognosis of such kind of coil embolization.

International Aneurysm CFD Challenge 2015: Solutions Using the Commercial Finite Volume Solver, Ansys CFX

AQiao1, W Fu2 and Y Hou1

1Beijing University of Technology, Beijing, 100124, China

2Beijing Union University, Beijing 100020, China

Purpose: To predict the likelihood of rupture in 5 cerebral aneurysms, computational fluid dynamics were carried out for these 5 models.

Methods:

  • Solver type: Finite volume.
  • Solver details: implicit.
  • Types of elements: tetrahedral and prisms (boundary layer).
  • Spatial grid resolution: Global element size is 0.08 mm; Minimum limit of element size is 0.01 mm. 5 layers of prism elements were assigned in boundary layer. The height of the first prism layer near the vessel wall is 0.04 mm and the height ratio of adjoining boundary layer is 1.1.
  • Maximum iteration number of time steps is 500 for steady flow and the convergence criterion is 10−5 for root mean square.
  • Boundary conditions: Velocity boundary conditions at the inlet are Poiseuille flow (steady flow).

The maximum speed (0.81 m/s) and mean speed (0.6 m/s) were assigned at the inlet respectively. Vascular wall was assumed to be rigid. No-slip boundary conditions were applied to the walls. Blood is assumed to be a Newtonian fluid. The flow is laminar. Blood pressure was set to 0 Pa at the exit section (two outlets for case1 case2 case3 and case5, three outlets for case4). The same boundary conditions and model parameters were used in the five cases.

Results: Pressure Loss Coefficient (PLC) was used to predict which aneurysm was the ruptured one according to the conclusion by Takao, who suggested that the values of PLC were lower in ruptured aneurysms (Takao et al., 2012). Based on our calculations, the values of PLC from case1 to case5 are 0.787, 0.7754, 0.874, 0.885 and 2.260 respectively. The difference of PLC in case1, case2, case3, case4 and case5 is significant.

Conclusion: So we predict that case5 is the unruptured one, and the others are the ruptured ones.

Reference

43. Takao H, Murayama Y, Otsuka S, et al. Hemodynamic Differences Between Unruptured and Ruptured Intracranial Aneurysms During Observation. Stroke 2012; 43: 1436–1439. [PubMed]

Flow Analysis in Recanalization of Cerebral Aneurysms After Coil Embolization using Magnetic Resonance Fluid Dynamics (MRFD)

TSano1, F Ishida2, U Yasuyuki3, N Toma3, S Hiroshi4 and S Hidenori3

1Department of Neurosurgery, Ise Red Cross Hospital, Ise, Mie, Japan

2Department of Neurosurgery, Mie University Graduate School of Medicine, Tsu, Mie, Japan

3Department of Neurosurgery, Mie Chuo Medical Center, NHO, Tsu, Mie, Japan

4InnovativeNeuro-InterventionRadiology, Mie University Graduate School of Medicine, Tsu, Mie, Japan

Purpose: The high recurrence rate after coil embolization of cerebral aneurysm is still disadvantage against clipping surgery. In morphological aspects large and wide neck aneurysms are previously reported to have tendency to be recurrent. During coiling low packing density and neck remnant and residual filling in immediate angiographic results also cause future recurrence. (Sluzewski, van Rooij et al., 2004) Moreover, several studies showed the hemodynamic feature is involved in recanalization using computational fluid dynamics (CFD)(Luo, Yang et al., 2011) and flow dynamics studies using phase contrast magnetic resonance imaging (PC-MRI). (Kono and Terada 2014) These studies are retrospective and analysed coiled aneurysms and few studies focused on preoperative aneurysmal flow dynamics assessment for risk of recanalization. This prospective study was performed to evaluate the relationship of preoperative flow dynamics of cerebral aneurysm and recanalization.

Materials and Methods: From August 2012 to September 2013, we coiled 11 unruptured cerebral aneurysms. For each aneurysm, a preoperative four-dimensional (4D)-PC-MRI was performed. We obtained intra-aneurysmal velocity and volume using magnetic resonance fluid dynamics (MRFD). 6–12 months after coil embolization aneurysms were classified into recanalization (n = 3) or unchanged (n = 8) groups based on the angiographic appearance. Flow parameters involved in neck plane of aneurysm were calculated. Flow parameters, morphological parameters and packing density were compared between recanalization and unchanged groups.

Results: Flow analyses were completely calculated in all aneurysms (mean size, 10.13 mm). The inflow volume (P = 0.049) and velocity (P = 0.049) of neck plane of aneurysm were significantly larger in the recanalization group. Among morphological parameters, maximum dome size (P = 0.030) was significantly larger and packing density (P = 0.024) was significantly lower in recanalization group.

Conclusion: We first demonstrated relationship of preoperative flow analysis of cerebral aneurysm based MRFD and recanalization after coil embolization. MRFD may provide predictable flow information to reduce high recurrence rate.

References

44. Kono K, Terada T. Flow visualization of recurrent aneurysms after coil embolization by 3D phase-contrast MRI. Acta Neurochir (Wien) 2014; 156(11): 2035–2040. [PubMed]
45. Luo B, et al. High shear stress and flow velocity in partially occluded aneurysms prone to recanalization. Stroke 2011; 42(3): 745–753. [PubMed]
46. Sluzewski M, et al. Relation between aneurysm volume, packing, and compaction in 145 cerebral aneurysms treated with coils. Radiology 2004; 231(3): 653–658. [PubMed]

Numerical Simulations of Post-Surgical Flow and Thrombosis in Basilar Artery Aneurysms

SSeshadhri1, M Lawton2, L Boussel3, D Saloner4 and V Rayz1

1Department of Neurosurgery, Medical College of Wisconsin, Milwaukee,WI, USA

2Department of Neurological Surgery, University of California, San Francisco, San Francisco, CA, USA

3Department of Radiology, Louis Pradel Hospital, Creatis, LRMN, Lyon, France

4Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, CA, USA

Purpose: The treatment of fusiform cerebral aneurysms is a major challenge for neurosurgeons since it is often impossible to exclude these lesion from the circulation. In some cases, fusiform basilar artery aneurysm not amenable to stenting or coiling, can be treated by clipping some of the vessels feeding the aneurysm as well as adding a bypass to supply downstream vasculature. The goal of such treatment is to reduce the flow into the aneurysm in order to prevent it further progression and rupture. The surgeons have a limited information on the potential impact of the intervention on the flow patterns and subsequent thrombus deposition. Patient-specific CFD models based on medical imaging data can provide guidance by simulating postoperative flow fields that would result from alternative treatment options.

Method: In this study alternative surgical options were evaluated for three patients with fusiform aneurysms of the basilar artery. Patient-specific models were generated from contrast-enhanced MR angiography data obtained prior to the treatment. The inflow conditions were prescribed using phase-contrast MR velocimetry measurements. Several treatment scenarios were simulated for each patient by changing the model’s geometry to calculate the flow fields and to predict the flow field that would occur after the interventions. Computational domain consists of around 1 million unstructured tetrahedral elements generated using mesh generation tool Hypermesh by ALTAIR, and imported to ANSYS Fluent for the simulation. Unsteady patient specific inlet flow conditions were used under Newtonian fluid with rigid wall and incompressible flow assumptions. Virtual contrast injection were also carried out to estimate the flow residence time - a hemodynamic parameter related to intra-aneurysmal thrombus deposition.

Results: The results indicated the intra-aneurysmal regions with increased likelihood of thrombus deposition that would result from each surgical treatment. Some of the considered procedures would result in compromised flow through the vital branches of the basilar artery not compatible with patient’s survival. Based on comparison of the postoperative flows modelled for alternative procedures, it was demonstrated that an option involving a clipping of the posterior cerebral arteries accompanied with bypasses from the anterior circulation is likely to provide the most favourable outcomes. The contrast transport results show a delay in flow to the basilar artery thus inducing self-thrombosis.

Conclusion: Our results can help explain in vivo thrombus formation within an aneurysm after surgical intervention that is compatible with local hemodynamics. A detailed result will be shown in the conference. This demonstrates that CFD modeling can help improve the outcome of surgeries altering the flow in basilar aneurysms.

Validation of New Outlet Boundary Condition for CFD Simulation in Carotid Artery Stenosis Cases

KShinohara1,5, H Takao1,3, T Suzuki1, S Masuda3, T Suzuki3, Y Kambayashi2, C Dahmani3,4, T Ishibashi3, Y Qian5, M Yamamoto6 and Y Murayama3

1Graduate School of Mechanical Engineering, Tokyo University of Science, Japan

2Omori Red Cross Hospital, Japan

3Department of Neurosurgery, Jikei University School of Medicine, Japan

4Siemens Japan K.K., Japan

5The Australian School of Advanced Medicine, Macquarie, Australia

6Department of Mechanical Engineering, Tokyo University of Science, Japan

Purpose: Currently, computational fluid dynamics (CFD) is a widely used analysis method in the medical field, and there are many studies investigating carotid lesions. However, outlet boundary conditions strongly affect CFD results. This is particularly remarkable in cases with high ICA stenosis rates. In these cases, there is still no appropriate outlet boundary condition. For this problem, new approaches of setting outlet boundary conditions are proposed for CFD simulations of the human common carotid arteries (CCAs) bifurcation based on the concept of energy loss minimization at flow bifurcation (Qian et al., 2013). The purpose of this study is to investigate whether this approach is appropriate for CFD simulations in CCAs with high ICA stenosis ratios.

Methods: This study included patient-specific models from 19 patients who had high ICA stenosis ratios (>65%). Three-dimensional surface data were obtained from the angiography images. ANSYS 15.0 package (ANSYS, Canonsburg, Pennsylvania, USA) was used for both mesh generation and blood flow simulation. The minimum energy loss (MEL) method was used for the outlet boundary condition. The QICA/QCCA outflow ratios of boundary condition of MEL method through the CCA (QCCA), ICA (QICA) were calculated. We compared the CFD results of this outlet boundary condition with experimental data (Groen et al., 2010).

Results: The CFD results indicated that the tendency of outflow ratios is similar to that of empirical relationship. The statistical analysis of covariance (ANCOVA) showed no significant difference between the QICA/QCCA of MEL methods and the empirical relationship. (P = 0.68)

Conclusion: We found the QICA/QCCA outflow ratios of MEL method had no significant difference with the empirical relationship. The MEL outflow boundary condition may be appropriate for CFD simulation in the case of high ICA stenosis ratio.

Embedding Quality into Interaction Between Animal Models and Mechanical Evaluation

YShiraishi1, K Sasaki1, Y Inoue2, H Miura1, Y Inoue1, T Kitano3, C Shonai4, S Katahira4, Y Saiki4, T Yambe1, R Kawashima5 and N Kasai6

1PreClinical Research Center, Institute of Development, Aging and Cancer, Tohoku University, Sendai, Japan

2Institute for Experimental Animals, Institute of Development, Aging and Cancer, Tohoku University, Sendai, Japan

3Graduate School of Biomedical Engineering, Tohoku University, Sendai, Japan

4Department of Cardiovascular Surgery, Tohoku University Hospital, Sendai, Japan

5Institute of Development, Aging and Cancer, Tohoku University, Sendai, Japan

6Center for Laboratory Animal Research, Tohoku University, Sendai, Japan

As our labs shift our focus to broaden translational research more, it will be important to characterize animal experiment models and mechanical evaluation systems that might fall on us for the artificial internal organ research as well as the development of medical devices or therapeutic methodologies. In order to share the preclinical evaluation systems using large animals and mechanical circulatory models, we placed a new institutional function of preclinical research to be in an academic specific repository based on the biomedical research network in Tohoku University for the first step. These clinically indirect preparation work that may not lead to a breakthrough in the treatment or therapy will be useful to bridge between the developmental research to the clinical trials as well as to carry out any qualified therapeutic attempt with the basis of the new animal and mechanical evaluation quality systems. In the study, some specific projects including the prevention and anticipation of thrombogenesis during the ex-vivo circulatory support using ventricular assist devices were introduced based on the chronic animal studies and the mechanical observation circulatory models.

Prognosis of Cerebral Aneurysm After Surgical Flow Diversion

MShojima1, T Kimura2, A Morita2, H Nakatomi1, K Kawai2 and N Saito1

1University of Tokyo, Bunkyo-ku, Tokyo, Japan

2NTT-east Medical Center, Shinagawa-ku, Tokyo, Japan

Purpose: Surgical flow diversion is one of the last resorts to manage refractory cerebral aneurysms.

However, some aneurysms might enlarge or rupture even after successful surgical flow diversion. In order to investigate how the aneurysms respond after flow diversion, three aneurysms were analysed retrospectively with CFD.

Material and Methods: Two aneurysms ruptured and the other aneurysm shrank after surgical flow diversion. Three-dimensional steady CFD simulations were performed retrospectively with 3D-CT angiography obtained before and after surgical flow diversion using a finite-volume solver SCRYU/Tetra (Software Cradle, Osaka, Japan). Blood was treated as an incompressible Newtonian fluid. Vessel wall was treated as rigid. The inlet flow volume was scaled to make the WSS at the inlet 2.0 Pa and it was re-distributed according to the Poiseuille law. The flow volume was allocated to each outlet of the vessel geometry according to the Murray’s law.

Results: Case 11: Antegrade flow of basilar artery was obliterated by clipping of basilar artery in a case of a giant basilar tip aneurysm with a sufficient posterior communicating artery. This flow diversion resulted in 60% reduction of the aneurysm flow, but the WSS increased by two times and resulted in rupture.

Case 2: Distal vertebral artery was obliterated to reduce the outlet of a giant vertebral artery aneurysm involving posterior inferior cerebellar artery. The aneurysm flow was reduced, however, the increased flow resistance resulted in the increased wall stress and the aneurysm ruptured eventually.

Case 3: Antegrade flow of internal carotid artery was obliterated with EC/IC bypass in a case of a recurrent large internal carotid artery aneurysm. After surgery, the flow dynamic stress reduced and the aneurysm shrank.

Conclusion: It is not easy to predict the aneurysm prognosis after flow diversion, however, the CFD analysis and the accumulation of the cases might improve our prediction.

Reference

47. Shojima M, Morita A, Kimura T, Oshima M, Kin T, Saito N. Computational fluid dynamic simulation of a giant basilar tip aneurysm with eventual rupture after hunterian ligation. World Neurosurg. 2014; 82(3–4): 535 e5–9. [PubMed]

Virtual Stent Deployment

KSpranger1 and Y Ventikos1

1University College London, London, UK

Purpose: The effectiveness of intracranial stenting depends on a number of factors such as the released configuration of the stent, alteration of the vessel haemodynamics, incidence of an arterial injury, etc. (Pierot, 2011). However, there is currently no means for a clinician to obtain this vital information in clinical setting. Additionally, knowing the accurate positioning of the device inside the vessel would enable the subsequent blood flow analysis and possible prevention of such complications as stent migration, endoleakage, etc. Motivated by this clinical need, this study aimed at modelling virtual deployment of stents with fast computational times to be used in clinical practice.

Method: We modelled stent expansion process based on springs analogy (Blom, 2000), where stent structure is represented as a mesh of springs. Further, we have compared 3 different methods with different springs’ properties: lineal, semi-torsional and torsional springs. The comparison was based on the expansion of two devices – a stent and a flow diverter – in the case of free expansion, in the idealised straight and bent vessels and in real patient cases.

Results: The 3 spring analogy methods converged; however, they did so at different rates. The convergence was assessed by measuring displacements and force evolution. One of the interesting findings was the fact that the lineal springs method displayed faster convergence. Additionally, it produced final results comparable with those obtained by its more sophisticated semi-torsional and torsional counterparts. This was surprising since the lineal method constitutes the base for the other two methods and is associated with the simplest implementation.

Conclusion: Our study demonstrated the overall ability of spring-based methods to model virtual stent expansion in a computationally expedient manner, which constitutes a valuable base for future extensions of the model, with the ultimate goal of enabling predictive simulations of the minimally invasive methods in clinical setting.

References

48. Blom F. Considerations on the spring analogy. International Journal for Numerical Methods in Fluids 2000; 32(6): 647–668.
49. Pierot L. Flow diverter stents in the treatment of intracranial aneurysms: Where are we? Journal of Neuroradiology 2011; 38: 40–46. [PubMed]

How do Porosity and Pore Density of a Flow Diverter Affect the Flow Reduction Effect?

TSuzuki1, H Takao1,2, K Shinohara1, S Fujimura1, S Takayama1, T Suzuki2, C Dahmani2,3, S Masuda2, H Mamori4, T Ishibashi2, M Yamamoto4 and Y Murayama2

1Graduate School of Mechanical Engineering, Tokyo University of Science, Katsushika-ku, Tokyo, Japan

2Department of Neurosurgery, Jikei University School of Medicine, Minato-ku, Tokyo, Japan

3Siemens Japan K.K., Shinagawa-ku, Tokyo, Japan

4Department of Mechanical Engineering, Tokyo University of Science, Katsushika-ku, Tokyo, Japan

Purpose: It has been reported that “porosity” and “pore density” are the major factors determining the flow reduction effect of a flow diverter stent (FD). Many variations of stents can be designed by changing those two specifications. Therefore, it is important to understand the relation between the reduction effect of a FD and its porosity or pore density, in order to design useful and effective stents. Investigating this relation was the aim of this study.

Materials and Methods: An idealized sidewall IA model, composed of a spherical aneurysm of diameter 10 mm and a parent artery of diameter 4 mm, was generated. Additionally, 5 variations of the stent model, having the same porosity but different pore densities and strut sizes were generated (strut size: d = 0.030, 0.035, 0.040, 0.045, 0.050 mm). Furthermore, 3 of the 5 first models were selected (strut size d = 0.030, 0.040 and 0.050 mm) and for each one of them, 2 variations with different porosities were created. Finally, computational fluid dynamics (CFD) simulations were performed in the models without and with stent configurations. The reduction ratios (pre/post deployment) of velocity, wall shear stress (WSS) and inflow rate were processed and compared among the stents.

Results: With the stent of porosity 79.8%, pore density 5.2 pores/mm2 and strut size 0.045 mm, the reduction rates of velocity, WSS and inflow rate were 75.5%, 38.6% and 90.0% respectively. With the stent of porosity 84.6%, pore density 7.1 pores/mm2 and strut size 0.030 mm, these values were 75.4%, 37.0% and 89.9%, respectively, leading to the same reduction effects in both cases.

Conclusion: By changing the combination of wire density and porosity, stents having different specifications but the same efficacy can be designed. Further investigations with respect to other characteristics such as mechanical properties may lead to optimized stent implementations.

Numerical Study on the Effect of STA-MCA Anastomosis Position on Its Mass Flow Rate

STakayama1, M Watanabe2, H Takao1,2, T Suzuki1, K Shinohara1, S Fujimura1, T Suzuki2, C Dahmani2,3, H Mamori4, T Ishibashi2, M Yamamoto4 and Y Murayama2

1Graduate School of Mechanical Engineering, Tokyo University of Science, Katsushika-ku,Tokyo, Japan

2Department of Neurosurgery, The Jikei University School of Medicine, Minato-ku, Tokyo, Japan

3Siemens Japan K.K., Shinagawa-ku, Tokyo, Japan

4Department of Mechanical Engineering, Tokyo University of Science, Katsushika-ku, Tokyo, Japan

Purpose: To prevent stroke, an STA-MCA anastomosis is often performed to increase cerebral artery perfusion. However, there are no general criteria on its efficiency, and the failure shown in COSS study exemplifies that. If its efficiency can be predicted for each patient, the success rate will increase. This study aims to reveal the perfusion effect of anastomosis by investigating the post-operative flow field under various anastomosis conditions.

Materials and Methods: A patient who underwent bypass surgery in which a single STA was anastomosed to a M4 branch (MCA distal position), was analyzed by using computational fluid dynamics. The arterial vascular tree from the M4 part to the ICA, and their branches were included in the analysis. Two additional models: one with STA anastomosed to the M2- Superior trunk and the other - to the M2-Inferior trunk) were made, based on the above model. To investigate the influence on perforators, seven cylinders simulating perforators were added in these three geometries. RDH (Relative Difference to Healthy) was defined to measure how MFR (Mass Flow Rate) at each branch were close to the normal condition. Where, positive RDH indicated that patient’s MFR was more than that of normal adult, and negative RDH indicated that the MFR was less than that of normal adult, respectively.

Results: When STA was anastomosed to the M4 branch (STA-M4.), RDH was positive near the anastomosis, and negative at the proximal MCA. When anastomosed to the M2-Superior and Inferior trunk (STA-M2_Super., STA-M2_Infer.), RDH became positive at all branches. For perforators, the RDH was not higher than −10.1% in the STA-M4, while, in the STAM2_Super. and STA-M2_Infer. models, it was at least +31.1% and +27.5%, respectively.

Conclusion: The STA-M2 surgical technique would provide better perfusion than the STAM4 one.

Stagnation and Complex Flow in Ruptured Cerebral Aneurysms: A Possible Association with Hemostatic Pattern

MTsuji1, F Ishida2, I Tatsuya3, M Youichi4, S Masato2, T Sano5, T Hiroshi2, U Yasuyuki1, S Shinichi2 and S Hidenori1

1Department of Neurosurgery, Mie University Graduate School of Medicine, Tsu, Mie, Japan

2Department of Neurosurgery, Mie Chuo Medical Center, Tsu, Mie, Japan

3Department of Neurological Surgery, Research Institute for Brain and Blood Vessels, Akita, Akita, Japan

4Department of Neurosurgery, Suzuka Kaisei Hospital, Suzuka, Mie, Japan

5Department of Neurosurgery, Ise Red Cross Hospital, Ise, Mie, Japan

Purpose: Histopathological examination revealed that ruptured cerebral aneurysms had different hemostatic patterns depending on the location of the clot formation. In this study, we determined whether the hemostatic patterns had specific hemodynamic features on the computational fluid dynamics (CFD) analysis.

Materials and Methods: Twenty-six ruptured middle cerebral artery aneurysms were evaluated by three-dimensional (3D) computed tomographic (CT) angiography, and then harvested at surgical clipping. Histopathological examination determined the hemostatic patterns at the rupture points, and the patient-specific geometries were generated as stereolithography (STL) using preoperative 3D CT angiography. Numeral modelling was performed using a CFD package (ANSYS CFX CFD15.0; ANSYS Inc., Canonsburg, PA, USA). Blood was assumed to be incompressible Newtonian fluid with a density of 1056 kg/m3 and a viscosity of 0.0035 Pa s. CFD simulation were performed under pulsatile flow conditions driven from typical flow waveform of phase-contrast magnetic resonance imaging was scaled to achieve a physiological wall shear stress (WSS), and the following parameters were calculated: WSS, WSS-related hemodynamic parameters at the dome and invariant Q for the vortex core detection. The morphological and hemodynamic parameters were compared among the hemostatic patterns.

Results: The hematoxylin-eosin stain of the aneurysm wall including rupture points showed 13 inside pattern, 9 outside pattern and 4 other pattern aneurysms. Among 26 aneurysms, 3 aneurysms were excluded because their geometry models could not be generated for low vascular CT values. A Mann-Whitney U test revealed that smaller aneurysm size, lower gradient oscillatory number, lower Invariant Q and higher aneurysm formation indicator was significantly related to the inside pattern aneurysms.

Conclusion: The inside pattern aneurysms may have simpler flow patterns and less flow stagnation compared with the outside pattern aneurysms. CFD may be useful for diagnosing the hemostatic pattern of ruptured cerebral aneurysms.

References

50. Ford MD, et al. An objective approach to digital removal of saccular aneurysms: technique and applications. Br J Radiol 2009; 82: 55–61. [PubMed]
51. Lei M, et al. A forcal stresss gradient-dependent mass transfers mechanism for atherogenesis in branching arteries. Med Eng Phys 1996; 18: 326–332. [PubMed]
52. Mantha A, et al. Hemodynamics in a cerebral artery before and after formation of an aneurysm. AJNR Am J Neuroradiol 2006; 27: 1113–1118. [PubMed]
53. Meng H, et al. High wss or low wss? Complex intractions of hemodynamics with intracranial aneurysm initiation, growth, and rupture: toward a unifying hypothesis. AJNR Am J Neuroradiol 2014; 35: 1254–1262. [PubMed]
54. Murray CJ. The physical principle of minimum work applied to the angle of branching of arteries. J Gen Physiol 1926; 9: 835–841. [PMC free article] [PubMed]
55. Ryuta Y, et al. Aneurysmvolume-to-ostium area ratio: a parameter useful for discriminating the rupture status of intracratinial aneurysms. Nerurosugery 2011; 68: 477–488. [PubMed]
56. Tatsuya I, et al. How does spontaneous haemostasis occur in ruptured cerebral aneurysms? Surg Neurol 2006; 66: 269–276. [PubMed]
57. Tatsuya I, et al. Pathologicalconsiderationforhemostatic clot on ruptured cerebral aneurysms. Surg Cereb Stroke 2012; 40: 223–228.
58. Yoichi M, et al. Low wall shear stresss is independently associated with the rupture status of middle cerebral artery aneurysm. Stroke 2013; 44: 519–521. [PubMed]
59. Yuji S, et al. Can temporal fluctuation in spatiall wall shear stresss gradient initiate a cerebral aneurysm? A proposed novel hemodynamic index, the gradient oscillatory number (GON). J Biomech 2009; 42: 550–554. [PubMed]

An ‘Onion-Skin’ Multilayer Type of Model for Thrombus Formation

FTurjman5, Y Zhang1, O Faruk Eker1,2, O Malaspinas1,2, K Zouaoui Boudjeltia4, B Chopard3 and G Courbebaisse1

1CREATIS, INSA Lyon, Lyon, France

2Department of interventional neuroradiology, CHRU Montpellier, Montpellier, France

3Computer Science Department, University of Geneva, Geneva, Switzerland

4Laboratory of Experimental Medicine, CHU Charleroi-Hop Vesale, Charleroi, Belgium

5Hospital Pierre Wertheimer – HCL, Lyon, France

Purpose: Specific biological mechanisms helps make thrombus in the cavity of a patient-specific intracranial aneurysm but the underlying processes are often not widely known. Specialized biological endpoints play an essential role in the healing of the treated patient. Therefore, the objective of the presented multidisciplinary research concerns the modelling of the formation of a thrombus mimicking onion-skin behaviour and investigates the effect of blood flow velocity on thrombus formation.

Materials and Methods: This scientific research is a patient-oriented research which focuses on the choice of biological phenomena and biophysical interactions involved in the thrombus growth process by using an efficient Computational Fluid Dynamics tool implemented via the lattice Boltzmann method. Low wall shear stresses, which can significantly influence the endothelial cells’ behaviour, are selected to be the trigger of the whole process of the thrombosis (Ouared et al., 2008). A giant patient-specific aneurysm case is taken in consideration which formed thrombus spontaneously; different velocity profiles are applied in order to estimate their influence on the initialization of the different phenomena leading to the thrombus formation, such as platelets’ aggregation.

Results: Thrombus formation with onion-skin structure is investigated and by changing the magnitude and the pulsatility index based on the upstream-downstream gradient, the thrombus formation can be triggered. Different locations and final shapes of the thrombus are also observed through the results generated by the numerical simulation. The preliminary results show that the magnitude and the pulsatility index of velocity profile can play an important role for initiating thrombus formation and the final shape of the thrombus.

Conclusion: This study will not only have important repercussions in understanding the thrombus formation process, but also in providing an in-depth knowledge to deliver optimized endovascular treatment for each patient.

Reference

60. Ouared R. Thrombosis modelling in intracranial aneurysms: a lattice Boltzmann numerical algorithm. Computer Physics Communications 2008; 179: 128–131.

Computational Fluid Dynamics (CFD) Analysis Using Porous Media Modeling Predicts Angiographic Occlusion Status after Coiling of Unruptured Cerebral Aneurysms

YUmeda1, F Ishida2, M Tsuji1, K Furukawa2, R Yasuda1, N Toma1, H Sakaida2 and H Suzuki2

1Department of Neurosurgery, Mie University Graduate School of Medicine, Tsu, Mie, Japan

2Department of Neurosurgery, Mie Chuo Medical Center, Tsu, Mie, Japan

Purpose: This study was designed to develop a new hemodynamic parameter on the computational fluid dynamics (CFD) analysis using porous media modeling to predict the angiographic occlusion status after coil embolization of unruptured cerebral aneurysms preoperatively.

Methods: From January 2008 to December 2013, we treated 36 unruptured cerebral aneurysms with coil embolization. Aneurysms were classified into complete occlusion (CO, n = 18) or residual neck (RN, n = 11), residual aneurysm (RA, n = 7) groups based on the angiographic results at 6–12 months post-coiling. For each aneurysm, the CFD simulation was achieved using a preoperative patient-specific geometry and porous media modeling. With the assumption that filtration of blood through a virtual coil-filled aneurysm was described by the Darcy’s law (porous media modeling). A new hemodynamic parameter, residual flow volume (RFV) in the aneurysm dome, was calculated using the CFD simulation. Morphological parameters, volume embolization ratio (VER) and hemodynamic parameters were compared among 3 groups. The area under the receiver operating characteristic (ROC) curve (AUC) was used to examine the diagnostic accuracy to predict the 6–12-month post-coiling angiographic occlusion status.

Results: There were significant differences in Neck area, Aneurysm volume and VER among the 3 groups, in the multiple comparison, a significantly difference between the CO and RA groups. Among hemodynamic parameters, RFV were significantly differences in the multiple test and two significantly differences between the CO and RA groups, between the CO and RN groups, in the multiple comparison. The ROC analyses showed that RFV with an average flow velocity of more than 1.0 cm/sec (RFV1.0) was useful to predict the post-coiling aneurysm occlusion status (AUC, 0.91 [95% confidence interval, 0.82–1.00]; cut-off value, 15.9 mm3; sensitivity, 83%; and specificity, 83%).

Conclusion: A new hemodynamic parameter, RFV1.0 on the CFD analysis using porous media simulation may be useful to predict the post-coiling aneurysm-occlusion status.

Another EBM (Engineering Based Medicine)

MUmezu1, K Iwasaki1, K Sakaguchi1, T Yagi1, H Isaki1, H Karube1, I Sen2 and H Kasanuki1

1Waseda University, Tokyo, Japan

2Department of Biomedical Sciences, Macquarie University, New South Wales, Australia

“EBM” is widely recognized as an “Evidence Based Medicine”, however, we have proposed a new concept as “Another EBM: Engineering Based Medicine”. Our trial on practically interdisciplinary alliance has been conducted at TWIns, which is an abbreviation for Tokyo Women’s Medical University and Waseda University for Joint Institution. It was opened in 2008 as the first collaborative institution between a school of medicine and a school of science and engineering in Japan. The number of the residents is 600, including 300 graduate students, and 20% of the residents have a mechanical engineering background. In the biomechanical engineering section, we have established dry-laboratories, aiming at1 providing practical tools to assess safety and effectiveness of medical treatments and2 establishing reliable and practical test platforms for assessing the performances of keep-coming new medical devices. Throughout our trials, we have developed several types of mock circulatory system, some of them have an Australian pulsatile pump, called spiral vortex pump. Its hemodynamic advantage was verified by a laser-inducing 3D quantitative flow visualization technique. Recently, we have proposed a new approach on the pathological engineering study to fill the existing gap between physiology and pathology in an attempt to bring the engineering simulation into clinical medicine, because blood flows in human cerebral aneurysms are widely believed to be associated with the risk of rupture, but unsolved problems still exist.

Following the opening of TWIns, in 2010 we opened a joint graduate school that offers the first government-approved PhD degree program in Medical Regulatory Science. Recently, we have also opened “Institute for Medical Regulatory Science” at TWIns, aiming at a fusion among Clinical Medicine, Science, Engineering, Law, Economics, Politics and Ethics. We hope this unique environment will contribute to the future success of those who experience our approach with “Engineering Based Medicine”.

The Role of Patient-Specific Vessel Wall Thickness for the Rupture Prediction of Intracranial Aneurysms

S Voß1, PBerg1, T Hoffmann2, S Glaßer3, O Beuing2 and G Janiga1

1Department of Fluid Dynamics and Technical Flow, University of Magdeburg “Otto-von-Guericke”, Magdeburg, Germany

2Department of Neuroradiology, University Hospital Magdeburg, Magdeburg, Germany

3Department of Simulation and Graphics, University of Magdeburg “Otto-von-Guericke”, Magdeburg, Germany

Computational Fluid Dynamics (CFD) is known to have a huge potential to assist physicians during therapy planning at no risk for a patient harbouring an intracranial aneurysm. However, numerous simplifications are required in order to handle the computational effort. One of the primary assumptions is the consideration of non-flexible vessel walls. Due to limited temporal and spatial resolution of existing imaging methods, reliable assessment of wall properties such as thickness or elasticity is challenging.

In contrast to recent numerical investigations, which consider a constant wall thickness, this study incorporates local vessel wall differences. The complete Circle of Willis of a patient, who died from an untreated, ruptured aneurysm, was extracted post-mortem and the rupture site was identified by a neuroradiologist. The thickness of the inner and outer wall of the aneurysm and the parent artery were measured with intravascular ultrasound. After reconstruction of the geometry, CFD simulations considering fluid-structure interactions with 1) variable and 2) constant wall thickness allow the evaluation of its role regarding rupture prediction.

Preliminary results of the investigation indicate the importance of non-constant, non-rigid vessel walls. Compared to a non-flexible vessel, the wall shear stress distribution varies significantly. Furthermore, changes in the stresses and particularly in the locations of highest values were observed. Therefore, the consideration of rigid walls may lead to the prediction of false endangered regions or even the classification as a safe situation although the case possesses a high rupture risk.

To further evaluate the role of the patient-specific wall thickness regarding rupture risk assessment of intracranial aneurysms, qualitative and quantitative comparisons of the different numerical approaches will be presented at the conference. Hence, the reliability of CFD methods can be increased in order to make them applicable for a clinical use.

Therapeutic Effect Observation of Endovascular Recanalization to Treat Symptomatic Subacute or Chronic Vertebrobasilar Artery Occlusion

JWan1, Y Pan1, Y Fan1, S Ding1 and W Sun1

1Department of Neurosurgery, Ren Ji Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China

Objective: To observe the effect and feasibility of endovascular stent-assisted endovascular recanalization to treat intracranial symptomatic subacute or chronic vertebrobasilar artery occlusion.

Methods: Twelve patients with subacute or chronic vertebrobasilar artery occlusion were chosen in our study, including eight males and four females, the mean age is 58.5 years old. Each patients were attacked in significant symptoms of posterior circulation, and endovascular stent-assisted endovascular recanalization were performed in at least 3 days from the appearance of clinic symptoms. Neurological status of the patients before operation and 24 hours after stenting were assessed using the modulate RANK score (mRs score). All patients undergoing angiography were successfully accomplished with six months follow—up

Results: Successful recanalization was achieved in 11 of 12 patients. One patients failed to achieve recanalization for long occlusion time (more than six months). There were not any complications such as bleeding and stroke in operations. Improvement in neurologic function (mRs score) at 6 months was observed in all patients, and there were no re occlusion.

Conclusion: Endovascular stent-assisted endovascular recanalization is a safe and effective treatment method for symptomatic subacute or chronic vertebrobasilar artery occlusion.

Influence on Branch Arteries after Flow Diverter Deployed to Occlude Cerebral Aneurysms

SZWang1, C Wang2 and XJ Yang2

1Department of Mechanics and Engineering, Fudan University, Shanghai, China

2Beijing Neurosurgery Institute, Beijing, China

Purpose: To study the influence on the branch arteries when the flow diverters deployed to occlude the cerebral aneurysms.

Materials and Methods: A giant cerebral aneurysm involved a branch artery was treated virtually by three kinds of flow diverters (LVIS, Pipeline and Tubridge) with fast virtual deployment method (Larrabide et al., 2012 & Ma et al., 2013). The blood flow in the giant aneurysm before and after treatment was simulated by computational fluid dynamics method. The variations of the hemodynamic characteristics on the giant aneurysm and flow rate at the branch artery were investigated.

Results: When LVIS deployed, the flow rate at the branch artery was raised about 14%. When Pipeline deployed, the flow rate at the branch artery was raised about 12%. When Tubridge deployed, the flow rate at the branch artery was raised about 8%.

Conclusion: In the three flow diverters, Tubridge is the most effective to occlude the aneurysm when considering the reduction of the velocity inside the aneurysm sac. The three kinds of flow diverters do not occlude the branch artery even if they covered the orifice of the branch and they can increase the flow rate at the branch artery on the contrary.

References

61. Larrabide I, Kim M, Augsburger L, Villa-Uriol MC, Rufenacht D, Frangi AF. Fast Virtual Deployment of Self-Expandable Stents: Method and in vitro Evaluation for Intracranial Aneurysmal Stenting. Medical Image Analysis 2012; 16: 721–30. [PubMed]
62. Ma D, Dumont TM, Kosukegawa H, Ohta M, Yang X, Siddiqui AH, Meng H. High Fidelity Virtual Stenting (HiFiVS) for Intracranial Aneurysm Flow Diversion: In Vitro and In Silicon. Annals of biomedical engineering 2013; 41: 2143–2156. [PMC free article] [PubMed]

Parametric Imaging for the Objective Grading of Collateral Flow in Acute MCA Occlusion

WWen1, Y Fang1, P Yang1, Y Zhang1, J Ge2, Y Xu1, B Hong1, Q Huang1 and J Liu1

1Changhai Hospital, Shanghai, China

2Angiography & Interventional X-ray Systems, Healthcare Sector, Siemens Ltd., Shanghai, China

Purpose: To report a quantitative and objective way of leptomeningeal collateral assessment using parametric color coding digital substraction angiography (DSA).

Materials and Methods: Fifteen consecutive acute middle cerebral artery occulation who received endovascular reperfusion therapy were recruited. Target downstream territory (TDT) of Middle Cerebral Artery in anterior-posterior view and reference point of each patient was drawn by 5 raters separately. Two parameters, relative maximum density of TDT (rDensitymax) and peak time interval between reference and TDT (ΔPT) were measured and tested for inter-rater reliability using intra-class correlation coefficients (ICC). Only parameters with substantial inter-rater reliability (ICC  0.75) were assessed for correlation with both the American Society of Interventional and Therapeutic Neuroradiology collateral grading (ACG) system and clinical outcome to evaluate its efficacy in characterization of collateral quality.

Results: ICC of rDensitymax and ΔPT were 0.982, P<0.001 and 0.796, P<0.001, respectively. The parameter rDensitymax shows strong correlation with ACG score (r of Spearman correlation test is 0.928, P<0.001), yet ΔPT_average doesn’t (r = 0.327, P = 0.159). Partial correlation coefficient between rDensitymax and modified rankin scale (mRS) at 3 month is 0.563, P = 0.036; that of ΔPT and mRS is 0.119, P = 0.685, controlled by the state of reperfusion. A cut-off point of 0.224 in rDensitymax provided high sensitivity (0.875) and specifity (100%) to predict patients with favourable clinical outcome (mRS  2).

Conclusion: A quantitative collateral assessment method based on parametric color coding 2D-DSA may present an alternative over subjective evaluation of collateral in acute M1 occlusion cases.

New Technology for Visualizing Hemodynamic Changes Introduced by Flow Diverters at the Ostium of Patient-specific Pcom Aneurysm Models – Preliminary Results

JXu1, C Karmonik2, J Ge3, Q Huang1 and J Liu1

1Department of Neurosurgery, Changhai Hospital, Shanghai, China

2Cerebrovascular Center, Department of Neurosurgery, Houston Methodist Hospital, Houston TX, USA

3Angiography & Interventional X-ray Systems, Healthcare Sector, Siemens Ltd., Shanghai, China

Purpose: Treatment of PCOM aneurysms where the PCOM originated from the aneurysm dome using flow diverters (FD) is challenging due to the necessity of maintaining flow through this artery while obliterating the aneurysm. Computational fluid dynamics (CFD) simulations may be helpful to develop a better understanding of how hemodynamics is modulated after FD placement.

Materials and Methods: A new technique is presented for visualizing focal high velocities and pressures at the FD post treatment. Sampling the velocity field calculated with CFD by a porous medium patch constructed using the geometry from a virtual FD (calculated with a research CFD prototype, Siemens Healthcare GmbH) allows quantifying inflow into and outflow from the aneurysm and to put this into relation to flow changes in the PCOM artery.

Results: Feasibility of this new technique is illustrated by quantifying flow in proximal and distal parent artery, the inflow and outflow area at the ostium and the flow into the PCOM artery before and after FD treatment. Our preliminary results indicate that under certain flow conditions flow in the PCOM artery pre and post virtual FD treatment remains almost unchanged while reducing inflow into the aneurysm by 17.75%.

Conclusion: A new technology is presented based on advanced reconstruction of the aneurysm ostium for better understanding flow changes in PCOM aneurysm pre and post virtual FD treatment.

In Vitro Characterisation of Aneurismal Haemodynamics With and Without a Flow Diverter Using Particle Image Velocimetry

WYang1, DI Verrelli2, K Karunanithi2, W Chong3 and Y Qian2

1Laser Flow Diagnostic Laboratory, Mineral Resources Flagship, CSIRO, Victoria, Australia

2Department of Biomedical Sciences, Macquarie University, New South Wales, Australia

3Monash Medical Centre, Melbourne, Victoria, Australia

Background and Purpose: In vitro experimental investigations of haemodynamic profiles inside two patient-specific silicone models of intracranial aneurysms were carried out with the aid of a non-intrusive particle image velocimetry (PIV) measurement technique. Multi-plane fluid flow structures, including two-dimensional time-mean velocities as well as their fluctuating components, across the aneurysm model were obtained before and after the deployment of a flow diverting stent. Moreover a high-speed camera was employed to visualise the effectiveness of the flow diverter on intra-aneurysmal flow patterns.

Both qualitative and quantitative experimental data will not only help the fundamental understanding of the haemodynamic phenomena occurring in the intracranial aneurysms, but be utilised to validate the numerical predictions using computational fluid dynamics (CFD).

Materials and Methods: Two patient-specific, full-scale silicone models of aneurysms were fabricated using rapid prototyping and 3D printing techniques. The working fluid used was a mixture of sodium iodide, glycerol and distilled water with its refractive index matching to the silicone resin. The 2D PIV system consisted of a CCD camera, a Nd:YAG pulsed laser and a synchroniser. Rhodamine B fluorescent particles were used as the seeding particles for the PIV measurements. At each measuring plane, 400 pairs of successive images were taken at the laser repetition rate of 4 Hz. Hence a mean velocity flow pattern at that plane was obtained by statistically averaging 400 successive instantaneous velocity vector maps over a time period of approximately two minutes.

Results: The multi-plane intra-aneurysmal flow patterns under various flow rates from 80 ml/min to 470 ml/min were obtained before and after the deployment of the flow diverter. It was clearly observed from the quantitative PIV measurements that the overall averaged velocity magnitude at one particular plane had a four-to-seven-fold decrease for the cases with a flow diverter compared to those without a flow diverter; similar ratios were also found for the fluctuating velocity components. In general, both PIV and high-speed filming techniques were able to capture the fluid flow structures inside a particular geometry of aneurysm. The flow patterns ranged from a single large recirculation zone to complex multi-recirculation regions depending on the location of the measuring plane.

Conclusion: The results demonstrated that the quantitative PIV measurement technique is suitable for quantifying the intra-aneurysmal flow velocities, as well as their fluctuating components, at high resolution. Significant mean and fluctuating intra-aneurysmal velocity reductions were observed for aneurysms in which a flow diverting stent deployed, compared to those without a flow diverter.

Modeling of Blood Flow with Pathology in Cerebral Aneurysms

TYagi1, Y Tobe1, Y Hayashi2, K Kawamura1 and M Umezu1

1Waseda University, Tokyo, Japan

2Kitahara International Hospital, Tokyo, Japan

Aneurysmal wall pathology varies in space and presents site-dependent lesion, such as blister-like and hypertrophic natures. The present studies aimed to find a correlation between local blood flow and pathologies. Specific focus is given to the direction of wall shear stress vectors, by which the local flow was classified quantitatively into 1) parallel flow, 2) merging flow, 3) rotating flow, and 4) impinging flow. The data showed the full impinging flow matched the site of blister at the prediction rate of 90%, and rotating matched the site of sclerotic lesions at 80%. The results revealed the potential ability of flow-based diagnostics of aneurysmal wall pathology.

Visualization of Flow Patterns through the Aneurysmal Orifice after Flow Diverter Optimizations with Different Objective Functions

MZhang1, H Anzai2 and M Ohta3

1Graduate School of Engineering, Tohoku University, Sendai, Japan

2FRIS, Tohoku University, Sendai, Japan

3Institute of Fluid Science, Tohoku University, Sendai, Japan

Background and Purpose: Flow diverting stent (FDS) becomes increasingly favourable in treating giant and wide-neck brain aneurysms. Flow diversion efficiency is thought to be of great importance in predicting the prognosis of FDS treatment. To visualize the flow pattern through the aneurysmal orifice under different FDS implantation potentially helps engineers with the upgraded design of FDS device.

Methods: In this study, a deployed FDS device was mimicked by eight helices including 4 clockwise and 4 counter-clockwise clinging to the wall of the parent artery of an idealized aneurysm model. Different objective functions-aneurysmal average velocity (AAV) and aneurysmal maximum velocity (AMV)-were applied in obtaining better designs of FDS device. A pre-constructed combination(Anzai u. a., 2014) of lattice Boltzmann method (LBM) and simulated annealing (SA) procedure was used to automatically identify an optimal device shape. Visualization of flow patterns through the aneurysmal orifice was performed by using an open source post-processing software Paraview.

Results: We obtained the optimized FDS shapes after hundreds of SA iterations. Streamlines and velocity vectors through the aneurysmal orifice were obtained. The same tendency of FDS wires concentrating inside the bundle of inflow (BOI) area was identified by visualizing the optimization results. Flow reduction rate of the initial FDS structure has a reduction of 83.63% and 90.48% for AMV and AAV, respectively. Optimizations using AMV as objective function improved the AMV/AAV to 92.77% and 92.15%, respectively. Optimizations using AAV as objective function improved the AMV/AAV to 90.28% and 95.65%, respectively.

Conclusion: Visualization suggested that wires concentrating inside BOI area might be an important factor to divert blood from flowing into the aneurysmal luminal.

Reference

63. Anzai, Hitomi; Falcone, Jean-Luc; Chopard, Bastien; u. a. “Optimization of Strut Placement in Flow Diverter Stents for Four Different Aneurysm Configurations“. In: Journal of biomechanical engineering. 2014; 136 (6), S. 061006. [PubMed]

Photoluminescent Nanomaterials for Visualisation of Intracellular Molecular Trafficking, Diagnostics and Therapy

AVZvyagin1,3 and EM Goldys2

1MQ Biofocus Research Centre, Macquarie University, Sydney

2ARC Centre of Excellence “Centre for Nanoscale Biophotonics” Macquarie University, Sydney

3Laboratory of Optical Theranostics, N.I. Lobachevsky Nizhny Novgorod State University, Russia

Development of new approaches for the diagnosis and therapy of tumours (taken together, termed Theranostics) - one of the most dynamic areas of Biomedicine, where new nanomaterials afford new opportunities. The nanomaterial merits include: programmability of their physical and chemical properties; abundance of reactive functional groups on the surface; large effective surface area; optimum size, which determines preferential accumulation of nanoparticles in tumour tissue due to the so-called enhanced permeability and retention effect, EPR (Maeda, 2010). This paper reports on multifunctional theranostic agents based on a new-generation biologically compliant photoluminescent nanoparticles with unique optical properties – fluorescent nanodiamonds (Bradac, Gaebel et al., 2010), nanorubies (Edmonds, Sobhan et al., 2013) and upconversion nanoparticles (Guller, Generalova et al., 2015).

Reported here fluorescent nanodiamonds (FND), nanorubies and upconversion nanoparticles (UCNP) were applied to visualise and probe biomolecular processes in their comprehensive cellular context. The exceptional photophysical properties of these nanoparticle pushed the sensitivity limit to the single biomolecule detection, whereas the nanoparticles surface can host various surface moieties, enabling anchoring of targeting and/or therapeutic cargo molecules. These nanoparticle biocomplexes, e.g. FND-EGFP, nanoruby-DAMGO, (quantum dot)-somatostatin or UCNP-(mini-antibody) are pieced together to form hybrid nanocomplexes capable to enter cells or pathology lesions to enable diagnosis and therapy.

Optical imaging of our photoluminescent nanoparticles in cells using a home-built epiluminescent microscope allowed visualisation of single nanorubies on the hefty background of cell autofluorescence and fluorescence dye staining. Target-delivered UCNPs rendered breast adenocarcinoma cells conspicuous among normal cells. The in vivo accumulation of UCNPs in a tumour grafted on the chicken embryo chorioallantoic membrane via EPR is shown, demonstrating target-delivery of drugs to cancer sites. The therapeutic potential of such drugs as photodynamic therapy active miniSOG-mini-antibody loaded onto UCNP was also successfully demonstrated in cells.

References

64. Bradac C, Gaebel T, Naidoo N, Sellars MJ, Twamley J, Brown LJ, Barnard AS, Plakhotnik T, Zvyagin AV, Rabeau JR. Observation and control of blinking nitrogen-vacancy centres in discrete nanodiamonds. Nature Nanotechnology 2010; 5(5): 345–349. [PubMed]
65. Edmonds AM, Sobhan MA, Sreenivasan VK, Grebenik EA, Rabeau JR, Goldys EM, Zvyagin AV. Nano-Ruby: A Promising Fluorescent Probe for Background-Free Cellular Imaging. Particle & Particle Systems Characterization 2013; 30(6): 506–513.
66. Guller A, Generalova A, Petersen E, Nechaev A, Trusova I, Landyshev N, Nadort A, Grebenik E, Deyev S, Shekhter A and Zvyagin A. “Cytotoxicity and non-specific cellular uptake of bare and surface-modified upconversion nanoparticles in human skin cells.” Nano Research 2015; 1–17.
67. Maeda H. Tumor-selective delivery of macromolecular drugs via the EPR effect: Background and future prospects. Bioconjugate Chemistry 2010; 21(5): 797–802. [PubMed]

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