How do coil configuration and packing density influence intra-aneurysmal hemodynamics?

Therapeutic Effect of Targeted Deployment Filling Coils in the Treatment of Intracranial Aneurysms

Endovascular coil embolization is the primary therapeutic modality for intracranial aneurysms. Substantial reports have been found regarding the coil packing density and inflow jet. However, the hemodynamic effect of increasing the rate of tamponade in the inflow jet area within the aneurysm remains unclear. In this study, individualized geometries of six intracranial aneurysms were recruited: all six aneurysms were located in the internal carotid artery. Two groups were created by changing the position and orientation of the microcatheter for the release of the third segment of the filling coil. The finite element method was used to simulate coil deployment. Computational fluid dynamics was used to characterize hemodynamics in post-deployment aneurysms. The parameters evaluated included velocity reduction, wall shear stress (WSS), low WSS (LWSS), relative residence time (RRT), flow kinetic energy in the neck region of the aneurysms, and residual flow volume (RFV) in the aneurysms. At the peak time (t = 0.17 s), the targeted deployment group has similar proportion of LWSS area to conventional deployment groups: targeted 78.13% ± 34.59% versus normal 74.20% ± 36.94% (mean ± SD, p = 0.583). The targeted deployment group has a higher RRT area (targeted 16.84% ± 5.58% vs. normal 6.42% ± 5.67% [mean ± SD, p = 0.009]), smaller flow kinetic energy (targeted 9.43 ± 4.33 vs. normal 16.23 ± 5.92 [mean ± SD, p = 0.047]), and a larger RFV in the aneurysms (targeted 35.97 ± 24.35 mm3 vs. normal 25.80 ± 18.94 mm3 [mean ± SD, p = 0.44]). Inflow jets play an important role in the treatment of aneurysms, and deploying filling coils in accordance with inflow jets may result in a better hemodynamic environment.

Improving the accuracy of computational fluid dynamics simulations of coiled cerebral aneurysms using finite element modeling

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

How to perform intra-aneurysmal coil embolization after Pipeline deployment: a study from a hemodynamic viewpoint

BACKGROUND

Pipeline embolization device (PED) deployment combined with coil therapy for large complex intracranial aneurysms is effective and considered superior to PED deployment alone. However, the optimal strategy for use of coils remains unclear. We used patient-specific aneurysm models and finite element analysis to determine the ideal packing density of coils after PED placement.

METHODS

Finite element analysis was used to provide a higher-fidelity model for accurate post-treatment computational fluid dynamics analysis to simulate the real therapeutic process of PED and all coils. We then calculated and analyzed the reduction ratio of velocity to identify the hemodynamic change during PED deployment and each coil embolization.

RESULTS

Sixteen consecutive patients underwent PED plus coil procedures to treat internal carotid artery intracranial aneurysms. After PED deployment, the intra-aneurysmal flow velocity significantly decreased (15.3 vs 10.0 cm/s; p<0.001). When the first coil was inserted, the flow velocity in the aneurysm further decreased and the reduction was significant (10.0 vs 5.3 cm/s; p<0.001). Analysis of covariance showed that the effect of the reduction ratio of velocity of the second coil was significantly lower than that of the first coil (p<0.001)-that is, when the packing density increased to 7.06%, the addition of coils produced no further hemodynamic effect.

CONCLUSION

Adjunct coiling could improve the post-PED hemodynamic environment in treated intracranial aneurysms. However, dense packing is not necessary because the intra-aneurysmal hemodynamics tend to stabilize as the packing density reaches an average of 7.06% or after insertion of the second coil.

Hemodynamic mechanism of pulsatile tinnitus caused by venous diverticulum treated with coil embolization

BACKGROUND AND OBJECTIVE

Coil embolization has become a new treatment method for pulsatile tinnitus (PT) caused by sigmoid sinus diverticulum (SSD). Although this therapy has achieved good results in clinical reports, the hemodynamic mechanism of coils in the treatment of PT in SSD remained unclear.

METHODS

Finite element method (FEM) and computational fluid dynamics (CFD) were combined to explore the hemodynamic mechanism of coil embolization in SSD treatment. Three personalized geometric models of sigmoid sinus were established according to the CTA data of patients. Coil model were established by FEM, and the hemodynamic differences of SSD before and after coiling were compared by transient CFD method.

RESULTS

Velocity streamlines disappeared in the SSD after coiling. At the peak time (t1 = 0.22 s), the SSD-average velocity decreased in every patient. The average value of the decreased in three patients was 0.154 ± 0.028 m/s (mean ± SD). Wall average pressure (P_avg) also showed a decline in every patient. Average of decrements of three patients was 17.69 ± 4.91 Pa (mean ± SD). Average WSS (WSS_avg) was also reduced in every patient. The average value of WSS drop was 9.74 ± 3.02 Pa (mean ± SD). After coiling, the proportion of low-velocity region in the sigmoid sinus cortical plate dehiscence (SSCPD) area increased. Average of increments was 22.1 ± 5.36% (mean ± SD).

CONCLUSIONS

A reduction in SSD-average velocity, wall pressure, and WSS were the short-term hemodynamic mechanism of coil embolization for PT. Coil embolization increased the proportion of low-velocity region in the SSCPD area, thereby creating a hemodynamic environment that easily produced thrombus and protects blood vessels from the impact of blood flow. This phenomenon was the long-term effect of coil embolization.

Tailored Sac Embolization During EVAR for Preventing Persistent Type II Endoleak

BACKGROUND

Persistent type II endoleaks (ELIIp) occur in 8-23% of patients submitted to endovascular aneurysm repair (EVAR) and may lead to aneurysm progression and rupture. Intraoperative embolization of the abdominal aortic aneurysm (AAA) sac is effective to prevent their occurrence, however a method to achieve complete sac thrombosis has not been standardized yet. Aim of our study was to identify factors associated with prevention of ELIIp after intraoperative embolization, in order to optimize technical details.

METHODS

Patients at high risk for ELIIp, who underwent EVAR with AAA - sac coil embolization were prospectively collected into a dedicated database from January 2012 to March 2015. The endoluminal residual sac volume (ERV), not occupied by the endograft [ERV= AAA total volume (TV) - (AAA-thrombus volume (THV) + endograft volume (EgV)] was calculated on preoperative computed tomography and the concentration of coils implanted (CCoil= n coils implanted/ERV) for each patient was evaluated. AAA volumetric evaluation was conducted by dedicated vessels analysis software (3Mensio). ELIIp presence was evaluated by contrast-enhanced ultrasound at 6 and 12-month. Patients with ELIIp at 12 months (Group 1) were clustered and compared to patients without ELIIp (Group 2), in order to evaluate the incidence of ELIIp in patients undergone to preventive AAA-sac embolization, and identify the predictors of ELIIp prevention. Morphological potential risk factors for ELIIp such as TV, THV, VR% and EgV were also considered in all patients. Statistical correlation was assessed by Fisher Exact Test.

RESULTS

Among 326 patients undergone to standard EVAR, 61 (19% - M: 96.7%, median age: 72 [IQR: 8] years, median AAA diameter: 57 [IQR: 7] mm) were considered at high risk for ELIIp and were submitted to coil embolization. The median AAA total volume (TV) and median ERV were 156 (IQR: 59) cc and 46 (IQR: 26) cc, respectively. The median number and concentration of coils (IMWCE-38-16-45 Cook M-Ray) positioned in AAA-sac were 5 (IQR: 1) coils and 0.17 coil/cm³ (range 0.02-1.20). Among this high-risk population, the incidence of ELIIp was 29.5% and 23% at 6 and 12-month, respectively. Fourteen patients (23%) were clustered in Group1 and 47 (77%) in Group 2. Both groups were homogeneous for clinical characteristics and preoperative morphological risk factors. There were no differences in the preoperative median TV, AAA-thrombus volume (THV), %VR, EgV and number of implanted coils between Group1 and Group2. Patients in Group1 had a significantly higher ERV (59 [IQR: 13] cm³ vs. 42 [IQR: 27] cm³, P = 0.002) and lower CCoil (0.09 [IQR: 0.03] vs. 0.18 [IQR: 0.21], P = 0.006) than patients of Group2. ELIIp was significantly related to the presence of ERV > 49 cm³ (86 % vs. 42 %, Group1 and Group2 respectively, P = 0.006) and CCoil < 0.17coil/ cm³ (100% vs. 68%, Group1 e Group2 respectively, P = 0.014).

CONCLUSION

According with our results, Coil concentration and endoluminal residual volume can affect the efficacy of the AAA - sac embolization in the prevention of ELIIp, moreover CCoil ≥0.17coil/ cm³ maight be considered to determine the tailored number of coils.

Experimental Safety Evaluation of Inflated Assisting Balloons for Endovascular Surgery

Objective

The balloon-assisted technique is one of the methods used for cerebral aneurysm embolization. There are several applications of assisting balloons such as remodeling the neck of cerebral aneurysms, protecting blood vessel branches, and stabilizing the microcatheter. In this study, we measured the pressure inside inflated assisting balloons to assess safety or procedure.

Methods

A T-junction silicone model was used. The pressure inside the balloon inflated to the set herniation levels in the T-junction model was measured using a fiber pressure sensor. We compared the pressure and difference between each assisting balloon.

Results

The pressure required for inflating the balloon to the set herniation level in the T-junction model varied depending on the type of assisting balloon. The results suggest that differences in pressure among inflated balloons are likely attributable to differences in the materials used in the lumens of the balloons.

Conclusion

The pressure inside various inflated assisting balloons was measured for comparison and differences were found. This experiment contributes to the safety of the balloon-assisted technique.

Hemodynamic Effect of the Last Finishing Coils in Packing the Aneurysm Neck

Background: Using the finishing coils to densely pack the aneurysm neck is necessary. However, the exact hemodynamic effect of finishing coils in packing the aneurysm neck is unknown.

Objective: To evaluate the hemodynamic characteristics of finishing coils to densely pack the aneurysm neck, using finite element method simulation.

Methods: A computational study was performed based on a 44-year-old female patient with an unruptured wide-necked carotid-ophthalmic artery aneurysm treated with low-profile visualized intraluminal support stent-assisted coil embolization. Four computational fluid dynamics models including pre-treatment, post-stenting, common stent-assisted coil embolization (SACE), and common SACE with finishing coils were evaluated qualitatively and quantitatively.

Results: Compared with the baseline of pretreatment model (100%), sac-averaged velocity in post-stenting, common SACE, and common SACE with finishing coil models decreased to 95.68%, 24.38%, and 13.20%, respectively; high flow volume (>0.1 m/s) around the aneurysm neck decreased to 92.19%, 9.59%, and 5.57%, respectively; and mean wall shear stress increased or decreased to 107%, 25.94%, and 23.89%, respectively.

Conclusion: Finishing coils to densely pack the aneurysm neck can generate favorable hemodynamic modifications, which may decrease the recurrence.

Intra-aneurysmal pressure changes during stent-assisted coiling

We aimed to examine aneurysm hemodynamics with intra-saccular pressure measurement, and compare the effects of coiling, stenting and stent-assisted coiling in proximal segments of intracranial circulation. A cohort of 45 patients underwent elective endovascular coil embolization (with or without stent) for intracranial aneurysm at our department. Arterial pressure transducer was used for all measurements. It was attached to proximal end of the microcatheter. Measurements were taken in the parent artery before and after embolization, at the aneurysm dome before embolization, after stent implantation, and after embolization. Stent-assisted coiling was performed with 4 different stents: LVIS and LVIS Jr (Microvention, Tustin, CA, USA), Leo (Balt, Montmorency, France), Barrel VRD (Medtronic/ Covidien, Irvine, CA, USA). Presence of the stent showed significant reverse correlation with intra-aneurysmal pressure–both systolic and diastolic—after its implantation (r = -0.70 and r = -0.75, respectively), which was further supported by correlations with stent cell size–r = 0.72 and r = 0.71, respectively (P<0.05). Stent implantation resulted in significant decrease in diastolic intra-aneurysmal pressure (p = 0.046). Systolic or mean intra-aneurysmal pressure did not differ significantly. Embolization did not significantly change the intra-aneurysmal pressure in matched pairs, regardless of the use of stent (p>0.05). In conclusion, low-profile braided stents show a potential to divert blood flow, there was significant decrease in diastolic pressure after stent placement. Flow-diverting properties were related to stent porosity. Coiling does not significantly change the intra-aneurysmal pressure, regardless of packing density.

Variation of Mass Effect After Using a Flow Diverter With Adjunctive Coil Embolization for Symptomatic Unruptured Large and Giant Intracranial Aneurysms

Background: Mass effect associated with large or giant aneurysms is an intractable problem for traditional endovascular treatments. Preventing recurrence of aneurysms requires dense coiling, which may aggravate the mass effect. However, the flow diverter (FD) is a new device that avoids the need for dense coiling. This study was performed to investigate whether use of FDs with adjunctive coil embolization can relieve the aneurysmal mass effect and to explore the factors that affect the variation of compressional symptoms.

Methods: We retrospectively evaluated patients with compressional symptoms caused by unruptured aneurysms who underwent endovascular treatment with an FD with adjunctive coil embolization at our center from January 2015 to December 2017. Imaging follow-up included digital subtraction angiography (DSA) ranging from 11 to 14 months and magnetic resonance imaging (MRI) ranging from 24 to 30 months; the former was used to evaluate the intracavitary volume, and the latter was used to measure the variation of the mass effect. Follow-up physical examinations were performed to observe variations of symptoms.

Results: In total, 22 patients with 22 aneurysms were treated by an FD combined with coil embolization. All 22 patients underwent the last clinical follow-up. Regarding compressional symptoms, 12 (54.54%) patients showed improvement, 6 (27.27%) were fully recovered, and 6 (27.27%) showed improvement but with incomplete cranial palsy. However, five (22.72%) patients showed no change, four (18.18%) showed worsening symptoms compared with their preoperative state, and one (4.55%) died of delayed rupture. Seventeen of the 22 patients underwent MRI. Of these 17 patients, the aneurysm shrank in 13 (76.47%) and no significant change occurred in 4 (23.53%). In the multivariate analysis, a short duration from symptom occurrence to treatment (p = 0.03) and younger patient age (p = 0.038) were statistically significant factors benefiting symptom improvement, and shrinkage of the aneurysm was associated with favorable clinical outcomes (p = 0.006).

Conclusions: Use of the FD with adjunctive loose coil embolization might help to alleviate the compressional symptoms caused by intracranial aneurysms. Shrinkage of the aneurysm, a short duration of symptoms, and younger patient age might contribute to favorable outcomes of mass effect-related symptoms.

Software-based simulation for preprocedural assessment of braided stent sizing: a validation study

OBJECTIVE

The authors sought to validate the use of a software-based simulation for preassessment of braided self-expanding stents in the treatment of wide-necked intracranial aneurysms.

METHODS

This was a retrospective, observational, single-center study of 13 unruptured and ruptured intracranial aneurysms treated with braided self-expanding stents. Pre- and postprocedural angiographic studies were analyzed. ANKYRAS software was used to compare the following 3 variables: the manufacturer-given nominal length (NL), software-calculated simulated length (SL), and the actual measured length (ML) of the stent. Appropriate statistical methods were used to draw correlations among the 3 lengths.

RESULTS

In this study, data obtained in 13 patients treated with braided self-expanding stents were analyzed. Data for the 3 lengths were collected for all patients. Error discrepancy was calculated by mean squared error (NL to ML -22.2; SL to ML -6.14, p < 0.05), mean absolute error (NL to ML 3.88; SL to ML -1.84, p < 0.05), and mean error (NL to ML -3.81; SL to ML -1.22, p < 0.05).

CONCLUSIONS

The ML was usually less than the NL given by the manufacturer, indicating significant change in length in most cases. Computational software-based simulation for preassessment of the braided self-expanding stents is a safe and effective way for accurately calculating the change in length to aid in choosing the right-sized stent for optimal placement in complex intracranial vasculature.

Efficacy of LVIS vs. Enterprise Stent for Endovascular Treatment of Medium-Sized Intracranial Aneurysms: A Hemodynamic Comparison Study

Background: We conducted a computational fluid dynamics (CFD) study and compared the treatment of medium-sized intracranial aneurysms with LVIS and Enterprise stent-assisted coil embolization (SACE) to determine the effects of hemodynamic changes caused by different stent and coil packing densities (PDs) in endovascular treatment.

Methods: We enrolled 87 consecutive patients, with 87 medium-sized intracranial aneurysms (≥7, ≤ 12 mm), who underwent LVIS or Enterprise SACE. Aneurysms treated with LVIS SACE were allocated to the LVIS group, and the remainder were allocated to the Enterprise group. CFD were performed to assess hemodynamic alterations between before treatment, after stent deployment, and after SACE.

Results: One aneurysm recanalized in the LVIS group (n = 42), and five recanalized in the Enterprise group (n = 45) (recanalization rate: 2.4 vs. 11.1%, respectively; P = 0.108). Higher complete obliteration rate (P = 0.069) was found in the LVIS group. Velocity at the neck plane showed a greater reduction ratio than velocity and WSS of the aneurysm in both groups after stent deployment, while velocity and WSS of the aneurysm showed a greater reduction ratio after coil placement. Further, there was a greater reduction in velocity at the neck plane (59.52 vs. 39.81%), aneurysmal velocity (88.46 vs. 69.45%), and wall shear stress (WSS) (85.45 vs. 69.49%) on the aneurysm in the LVIS group (P < 0.001 for all). Specifically, the reduction ratio of velocity at the neck plane showed significant difference between the groups in the multivariate analysis (P = 0.013).

Conclusions : LVIS SACE showed a lower recanalization for endovascular treatment of medium-sized intracranial aneurysms, and the greater hemodynamic alterations might be the key factors.

Relationship between haemodynamic changes and outcomes of intracranial aneurysms after implantation of the pipeline embolisation device: a single centre study

BACKGROUND

Intracranial aneurysms are increasingly being treated by the placement of flow diverters; however, the factors affecting the outcome of aneurysms treated using flow diverters remain unclarified.

METHODS

The present study investigated 94 aneurysms treated with pipeline embolisation device placement, and used a computational fluid dynamics method to explore the factors influencing the outcome of aneurysms.

RESULTS

Seventy-six completely occluded aneurysms and 18 incompletely occluded aneurysms were analysed. Before treatment, inflow jets were found in 13 (72.2%) aneurysms in the incompletely occluded group and 34 (44.7%) in the completely occluded group (P = 0.292). After deployment of the pipeline embolisation device, inflow jets remained in nine (50%) aneurysms in the incompletely occluded group and nine (11.8%) in the completely occluded group (P = 0.001). In the incompletely occluded group, regions with inflow jets after treatment corresponded with the patent areas shown on follow-up digital subtraction angiography. The mean reduction ratios of velocity in the whole aneurysm and on the neck plane were lower in the incompletely occluded than in the completely occluded group (P = 0.003; P = 0.017). Multivariate analysis revealed that the only independent risk factors for incomplete aneurysm occlusion were the reduction ratios of velocity (in the whole aneurysm, threshold 0.362, P = 0.005; on the neck plane, threshold 0.273, P = 0.015).

CONCLUSIONS

After pipeline embolisation device placement, reduction ratios of velocity in the whole aneurysm of less than 0.362 and on the neck plane of less than 0.273 are significantly associated with a greater risk of aneurysm incomplete occlusion. In addition, the persistence of inflow jets in aneurysms is associated with incomplete occlusion in the inflow jet area.

Use of a First Large-Sized Coil Versus Conventional Coils for Embolization of Cerebral Aneurysms: Effects on Packing Density, Coil Length, and Durable Occlusion

OBJECTIVE

To investigate effects of using a large-sized coil first on embolizing cerebral aneurysms compared with conventional coils.

MATERIALS AND METHODS

Forty-six patients with 51 saccular intracranial aneurysms who underwent embolization with a large-sized coil first were enrolled as the large-sized coil group. There were 33 female and 13 male patients with a mean age of 56.9 ± 8.8 years. The treatment modality was coiling alone in 30 aneurysms and stent-assisted coiling in 21. Meanwhile, 50 patients with 53 intracranial aneurysms who were treated with conventional-sized coils were selected as the control conventional-sized coil group, including 36 female and 14 male patients with a mean age of 54.6 ± 5.8 years. The treatment modality was coiling alone in 29 aneurysms and stent-assisted coiling in 24 aneurysms. The occlusion rate, percent packing volume, total coil number and length, and follow-up occlusion rate were compared between the 2 groups.

RESULTS

Significantly (P < 0.001) decreased percent packing volume (19.54% ± 6.44% vs. 27.39% ± 5.68%), decreased coil number (2.98 ± 1.09 vs. 6.38 ± 1.65), and length (26.20 ± 26.57 vs. 44.35 ± 35.88 cm) were achieved in the large versus the conventional coil group. At angiographic follow-up of 8 months, only 1 aneurysm (2.2%) recurred in the large coil group compared with 5 aneurysms recurrent (11.1%) in the conventional coil group.

CONCLUSIONS

The use of a large-sized coil as the first one for embolizing cerebral aneurysms may be a better embolization strategy because it achieves similar initial occlusion rates, decreased packing density, decreased coil numbers and lengths, and reduced recurrence prevalence at follow-up.

Differences in hemodynamic characteristics under high packing density between the porous media model and finite element analysis in computational fluid dynamics of intracranial aneurysm virtual treatment

Objective

This study aimed to compare the hemodynamic differences among no sac (NOS), porous media (POM) and finite element analysis (FEA) models to investigate the recurrence-related risks for coiled intracranial aneurysms (IAs).

Methods

The study enrolled 10 patients with 11 IAs who received simple coiling treatment and hemodynamic simulations were performed for all IAs using the above three models. Velocity, wall shear stress (WSS) and residual flow volume (RFV) were calculated and compared in order to assess the model differences for both aneurysm sac and parent vessel regions.

Results

For parent artery regions, all three models produced similar flow patterns and quantification analysis did not indicate differences in velocity and WSS (p>0.05). For aneurysm sac regions, the FEA model resulted in higher sac-maximized (0.18 m/s vs 0.06 m/s) and sac-averaged velocity (0.013 m/s vs 0.007 m/s), and higher sac-averaged (0.55 Pa vs 0.36 Pa, p=0.006) and sac-maximized WSS (12.1 Pa vs 6.6 Pa) than the POM model. The differences in RFV between the POM and FEA models under 11 different isovelocity thresholds (0.0001 m/s, 0.001 m/s, 0.002 m/s, 0.005 m/s, 0.01 m/s, 0.02 m/s, 0.05 m/s, 0.1 m/s, 0.2 m/s, 0.5 m/s, and 1 m/s) showed that the POM RFV was generally larger than those of the FEA model.

Conclusions

Compared with the FEA model, the POM model provides a lower velocity and WSS and higher RFV for the aneurysm sac, which could lead to incorrect estimates of the recurrent risk of coiled IAs under high packing density.

Reconstructing patient-specific cerebral aneurysm vasculature for in vitro investigations and treatment efficacy assessments

Perianeurysmal hemodynamics play a vital role in the initiation, growth and rupture of intracranial aneurysms. In vitro investigations of aneurysmal hemodynamics are helpful to visualize and measure blood flow, and aiding surgical planning approaches. Improving in vitro model creation can improve the feasibility and accuracy of hemodynamic investigations and surgical planning, improving clinical value. In this study, in vitro models were created from three-dimensional rotational angiography (3DRA) of six patients harboring intracranial aneurysms using a multi-step process involving 3D printing, index of refraction matching and silicone casting that renders the models transparent for flow visualization. Each model was treated with the same commercially-available, patient-specific, endovascular devices (coils and/or stents). All models were scanned by synchrotron X-ray microtomography to obtain high-resolution imaging of the vessel lumen, aneurysmal sac and endovascular devices. Dimensional accuracy was compared by quantifying the differences between the microtomographic reconstructions of the fabricated phantoms and the original 3DRA obtained during patient treatment. True-scale in vitro flow phantoms were successfully created for all six patients. Optical transparency was verified by using an index of refraction matched working fluid that replicated the mechanical behavior of blood. Synchrotron imaging of vessel lumen, aneurysmal sac and endovascular devices was successfully obtained, and dimensional errors were found to be O(100 μm). The creation of dimensionally-accurate, optically-transparent flow phantoms of patient-specific intracranial aneurysms is feasible using 3D printing technology. Such models may enable in vitro investigations of aneurysmal hemodynamics to aid in treatment planning and outcome prediction to devise optimal patient-specific neurointerventional strategies.

Hemodynamic simulation of intracranial aneurysm growth with virtual silk stent implantation

Longitudinal hemodynamic assessment of intracranial aneurysms (IAs) with endovascular treatment is essential for clinical decision making. We proposed a hemodynamic simulation method to explore the hemodynamic characteristics of a certain growth process of IA with virtual Silk stent implantation. Eight growth point models of IA were created by applying a bidirectional linear growing algorithm on patient 3D rotational angiography images. Simulated experiments showed that the WSS and velocity were significantly decreased with virtual Silk stent implantation at all growth points considered. The simulations revealed the flow pattern and WSS characteristics of IA growth.

Numerical simulation of patient-specific endovascular stenting and coiling for intracranial aneurysm surgical planning

Background

In this study, we develop reliable and practical virtual coiling and stenting methods for intracranial aneurysm surgical planning. Since the purpose of deploying coils and stents is to provide device geometries for subsequent accurate post-treatment computational fluid dynamics analysis, we do not need to accurately capture all the details such as the stress and force distribution for the devices and vessel walls. Our philosophy for developing these methods is to balance accuracy and practicality.

Methods

We consider the mechanical properties of the devices and recapitulate the clinical practice using a finite element method (FEM) approach. At the same time, we apply some simplifications for FEM modeling to make our methods efficient. For the virtual coiling, the coils are modeled as 3D Euler–Bernoulli beam elements, which is computationally efficient and provides good geometry representation. During the stent deployment process, the stent–catheter system is transformed according to the centerline of the parent vessel since the final configuration of the stent is not dependent of the deployment history. The aneurysm and vessel walls are assumed to be rigid and are fully constrained during the simulation. All stent–catheter system and coil–catheter system are prepared and packaged as a library which contains all types of stents, coils and catheters, which improves the efficiency of surgical planning process.

Results

The stent was delivered to the suitable position during the clinical treatment, achieving good expansion and apposition of the stent to the arterial wall. The coil was deployed into the aneurysm sac and deformed to different shapes because of the stored strain energy during coil package process and the direction of the microcatheter.

Conclusions

The method which we develop here could become surgical planning for intracranial aneurysm treatment in the clinical workflow.

Packing of metalized polymer nanofibers for aneurysm embolization

Aneurysmal subarachnoid hemorrhage (SAH) is the extravasation of blood into the subarachnoid space and is fatal in most cases. Platinum coils have been used to fill the hemorrhage site and prevent the extravasation of blood. Here we explored the use of Pt-coated polymer nanofibers (NF) to prevent blood extravasation and were able to achieve improved results in vitro. The polymer nanofibers were produced via electrospinning and were subsequently electroplated with Pt, resulting in metalized nanofibers. These nanofibers were installed within a microfluidic channel, and the resulting reduction in the permeability was evaluated using a fluid similar to blood. Based on the obtained results, these newly developed nanofibers are expected to decrease the operation cost for SAH, owing to their reduced size and low material cost. Furthermore, it is expected that these nanofibers will be used in a smaller amount during SAH operation while having the same preventive effect. This should reduce the operational risk associated with the multiple steps required to place the Pt coils at the SAH site. Finally, the underlying hydrodynamic mechanism responsible for the reduced permeability of the synthesized nanofibers is described.

Effect of Local Coil Density on Blood Flow Stagnation in Densely Coiled Cerebral Aneurysms: A Computational Study Using a Cartesian Grid Method

Aneurysm recurrence is the most critical concern following coil embolization of a cerebral aneurysm. Adequate packing density (PD) and coil uniformity are believed necessary to achieve sufficient flow stagnation, which decreases the risk of aneurysm recurrence. The effect of coil distribution on the extent of flow stagnation, however, especially in cases of dense packing (high PD), has received less attention. Thus, the cause of aneurysm recurrence despite dense packing is still an open question. The primary aim of this study is to evaluate the effect of local coil density on the extent of blood flow stagnation in densely coiled aneurysms. For this purpose, we developed a robust computational framework to determine blood flow using a Cartesian grid method, by which the complex fluid pathways in coiled aneurysms could be flexibly treated using an implicit function. This tool allowed us to conduct blood flow analyses in two patient-specific geometries with 50 coil distribution patterns in each aneurysm at clinically adequate PD. The results demonstrated that dense packing in the aneurysm may not necessarily block completely the inflow into the aneurysm and local flow that formed in the neck region, whose strength was inversely related to this local PD. This finding suggests that local coil density in the neck region still plays an important role in disturbing the remaining local flow, which possibly prevents thrombus formation in a whole aneurysm sac, increasing the risk of aneurysm regrowth and subsequent recurrence.

Risk Factor Analysis of Recanalization Timing in Coiled Aneurysms: Early versus Late Recanalization

BACKGROUND AND PURPOSE

Long-term documentation of anatomic and angiographic characteristics pertaining to the timing of recanalization in coiled aneurysms has been insufficient. Our intent was to analyze and compare early and late-phase recanalization after coiling, identifying respective risk factors.

MATERIALS AND METHODS

A total of 870 coiled saccular aneurysms were monitored for extended periods (mean, 30.8 ± 8.3 months). Medical records and radiologic data were also reviewed, stratifying patients as either early (n = 128) or late (n = 52) recanalization or as complete occlusion (n = 690). Early recanalization was equated with confirmed recanalization within 6 months after the procedure, whereas late recanalization was defined as verifiable recanalization after imaging confirmation of complete occlusion at 6 months. A multinomial regression model served to assess potential risk factors, the reference point being early recanalization.

RESULTS

Posterior circulation (P = .009), subarachnoid hemorrhage at presentation (P = .011), second attempt for recanalized aneurysm (P < .001), and aneurysm size >7 mm (P < .001) emerged as variables significantly linked with early recanalization (versus complete occlusion). Late (versus early) recanalization corresponded with aneurysms ≤7 mm (P = .013), and in a separate subanalysis of lesions ≤7 mm, aneurysms 4-7 mm showed a significant predilection for late recanalization (P = .008). However, the propensity for complete occlusion in smaller lesions (≤7 mm) increased as the size diminished.

CONCLUSIONS

Although long-term complete occlusion after coiling was more likely in aneurysms ≤7 mm, such lesions were more prone to late (versus early) recanalization, particularly those of 4-7 mm in size. Long-term follow-up imaging is thus appropriate in aneurysms >4 mm to detect late recanalization of those formerly demonstrating complete occlusion.

Virtual endovascular treatment of intracranial aneurysms: models and uncertainty

Virtual endovascular treatment models (VETMs) have been developed with the view to aid interventional neuroradiologists and neurosurgeons to pre-operatively analyze the comparative efficacy and safety of endovascular treatments for intracranial aneurysms. Based on the current state of VETMs in aneurysm rupture risk stratification and in patient-specific prediction of treatment outcomes, we argue there is a need to go beyond personalized biomechanical flow modeling assuming deterministic parameters and error-free measurements. The mechanobiological effects associated with blood clot formation are important factors in therapeutic decision making and models of post-treatment intra-aneurysmal biology and biochemistry should be linked to the purely hemodynamic models to improve the predictive power of current VETMs. The influence of model and parameter uncertainties associated to each component of a VETM is, where feasible, quantified via a random-effects meta-analysis of the literature. This allows estimating the pooled effect size of these uncertainties on aneurysmal wall shear stress. From such meta-analyses, two main sources of uncertainty emerge where research efforts have so far been limited: (1) vascular wall distensibility, and (2) intra/intersubject systemic flow variations. In the future, we suggest that current deterministic computational simulations need to be extended with strategies for uncertainty mitigation, uncertainty exploration, and sensitivity reduction techniques. WIREs Syst Biol Med 2017, 9:e1385. doi: 10.1002/wsbm.1385 For further resources related to this article, please visit the WIREs website.

Optimal first coil selection to avoid aneurysmal recanalization in endovascular intracranial aneurysmal coiling

BACKGROUND

Aneurysmal recanalization is a problem with endovascular coiling and one of its risk factors is the low volume embolization ratio (VER). The first coil VER (1st VER) is believed to be critical for obtaining a high VER. The main objective of this study was to evaluate factors potentially useful for selecting the optimal 1st VER for endovascular coiling.

METHODS

609 initial saccular aneurysmal treatments performed between January 2010 and December 2014 at our institution were included in this retrospective study. Attempted procedures, retreatment cases, intraoperative rupture cases, and stent-assisted coiling cases were excluded. Age, sex, aneurysm location, ruptured aneurysm, aneurysm shape, neck size, maximum aneurysm size, dome-to-neck ratio, aneurysm volume, procedure, immediate Raymond scale score, 1st VER, and VER between the recanalization groups and non-recanalization groups were compared.

RESULTS

The factors related to recanalization were ruptured aneurysms, neck width, maximum aneurysm size, aneurysm volume, procedure, 1st VER, and VER. The cut-off values for aneurysm recanalization were a 1st VER of 10.0% and a VER of 33.0%. The maximum average VER of normal size aneurysms was found in the groups with a 1st VER of 17.5-20.0%.

CONCLUSIONS

1st VER was found to be a helpful index for estimating aneurysmal recanalization after coil embolization. The target 1st VER was 17.5-20.0% for obtaining a higher VER and avoiding recanalization.

Hemodynamic Characterization of Geometric Cerebral Aneurysm Templates Treated With Embolic Coils

Embolic coiling is one of the most effective treatments for cerebral aneurysms (CAs), largely due to the hemodynamic modifications that the treatment effects in the aneurysmal environment. However, coiling can have very different hemodynamic outcomes in aneurysms with different geometries. Previous work in the field of biofluid mechanics has demonstrated on a general level that geometry is a driving factor behind aneurysmal hemodynamics. The goal of this study was to relate two specific geometric factors that describe CAs (i.e., dome size (DS) and parent-vessel contact-angle (PV-CA)) and one factor that describes treatment (i.e., coil packing density (PD)) to three clinically relevant hemodynamic responses (i.e., aneurysmal root-mean-square velocity (Vrms), aneurysmal wall shear stress (WSS), and cross-neck flow (CNF)). Idealized models of basilar tip aneurysms were created in both virtual and physical forms to satisfy two-level multifactorial experimental designs. Steady and pulsatile flow hemodynamics were then evaluated in the virtual models using computational fluid dynamics (CFD) (before and after virtual treatment with finite element (FE) embolic coil models), and hemodynamics were also evaluated in the physical models using particle image velocimetry (PIV) (before and after treatment with actual embolic coils). Results showed that among the factors considered, PD made the greatest contributions to effects on hemodynamic responses in and around the aneurysmal sac (i.e., Vrms and WSS), while DS made the greatest contributions to effects on hemodynamics at the neck (i.e., CNF). Results also showed that while a geometric factor (e.g., PV-CA) may play a relatively minor role in dictating hemodynamics in the untreated case, the same factor can play a much greater role after coiling. We consider the significance of these findings in the context of aneurysmal recurrence and rupture, and explore potential roles for the proposed methods in endovascular treatment planning.

Successful Retreatment of Recurrent Intracranial Vertebral Artery Dissecting Aneurysms After Stent-Assisted Coil Embolization: A Self-Controlled Hemodynamic Analysis

BACKGROUND

Intracranial vertebral artery dissecting aneurysms (VADAs) tend to recur despite successful stent-assisted coil embolization (SACE). Hemodynamics is useful in evaluating aneurysmal formation, growth, and rupture. Our aim was to evaluate the hemodynamic patterns of the recurrence of VADA.

METHODS

Between September 2009 and November 2013, all consecutive patients with recurrent VADAs after SACE in our institutions were enrolled. Recurrence was defined as recanalization and/or regrowth. We assessed the hemodynamic alterations in wall shear stress (WSS) and velocity after the initial SACE and subsequently after retreatment of the aneurysms that recurred.

RESULTS

Five patients were included. After the initial treatment, 3 patients showed recanalization and 2 showed regrowth. In the 2 patients with regrowth, the 2 original aneurysms maintained complete occlusion; however, de novo aneurysm regrowth was confirmed near the previous site. Compared with 3 recanalized aneurysms, the completely occluded aneurysms showed high mean reductions in velocity and WSS after initial treatment (velocity, 77.6% vs. 57.7%; WSS, 74.2% vs. 52.4%); however, WSS remained high at the region near the previous lesion where the new aneurysm originated. After the second retreatment, there was no recurrence in any patient. Compared with the 3 aneurysms that recanalized, the 4 aneurysms that maintained complete occlusion showed higher reductions in velocity (62.9%) and WSS (71.1%).

CONCLUSIONS

Our series indicated that hemodynamics might have an important role in recurrence of VADAs. After endovascular treatment, sufficient hemodynamic reduction in aneurysm dome, orifice, and parent vessel may be one of the key factors for preventing recurrence in VADAs.

Computational fluid dynamics of cerebral aneurysm coiling using high-resolution and high-energy synchrotron X-ray microtomography: comparison with the homogeneous porous medium approach

BACKGROUND

Computational modeling of intracranial aneurysms provides insights into the influence of hemodynamics on aneurysm growth, rupture, and treatment outcome. Standard modeling of coiled aneurysms simplifies the complex geometry of the coil mass into a homogeneous porous medium that fills the aneurysmal sac. We compare hemodynamics of coiled aneurysms modeled from high-resolution imaging with those from the same aneurysms modeled following the standard technique, in an effort to characterize sources of error from the simplified model.

MATERIALS

Physical models of two unruptured aneurysms were created using three-dimensional printing. The models were treated with coil embolization using the same coils as those used in actual patient treatment and then scanned by synchrotron X-ray microtomography to obtain high-resolution imaging of the coil mass. Computational modeling of each aneurysm was performed using patient-specific boundary conditions. The coils were modeled using the simplified porous medium or by incorporating the X-ray imaged coil surface, and the differences in hemodynamic variables were assessed.

RESULTS

X-ray microtomographic imaging of coils and incorporation into computational models were successful for both aneurysms. Porous medium calculations of coiled aneurysm hemodynamics overestimated intra-aneurysmal flow, underestimated oscillatory shear index and viscous dissipation, and over- or underpredicted wall shear stress (WSS) and WSS gradient compared with X-ray-based coiled computational fluid dynamics models.

CONCLUSIONS

Computational modeling of coiled intracranial aneurysms using the porous medium approach may inaccurately estimate key hemodynamic variables compared with models incorporating high-resolution synchrotron X-ray microtomographic imaging of complex aneurysm coil geometry.

Precision Imaging: more descriptive, predictive and integrative imaging

Medical image analysis has grown into a matured field challenged by progress made across all medical imaging technologies and more recent breakthroughs in biological imaging. The cross-fertilisation between medical image analysis, biomedical imaging physics and technology, and domain knowledge from medicine and biology has spurred a truly interdisciplinary effort that stretched outside the original boundaries of the disciplines that gave birth to this field and created stimulating and enriching synergies. Consideration on how the field has evolved and the experience of the work carried out over the last 15 years in our centre, has led us to envision a future emphasis of medical imaging in Precision Imaging. Precision Imaging is not a new discipline but rather a distinct emphasis in medical imaging borne at the cross-roads between, and unifying the efforts behind mechanistic and phenomenological model-based imaging. It captures three main directions in the effort to deal with the information deluge in imaging sciences, and thus achieve wisdom from data, information, and knowledge. Precision Imaging is finally characterised by being descriptive, predictive and integrative about the imaged object. This paper provides a brief and personal perspective on how the field has evolved, summarises and formalises our vision of Precision Imaging for Precision Medicine, and highlights some connections with past research and current trends in the field.

Practical Feasibility and Packing Density of Endovascular Coiling Using Target® Nano™ Coils in Small Cerebral Aneurysms

Objective

Based on the use of Nano™ coils, we retrospectively compared the proportion of the coils (≤ 1.5 mm) and packing density in two patient groups with small cerebral aneurysms (< 4 mm diameter) who were treated with or without Nano™ coils.

Materials and Methods

Between January 2012 and November 2013, in 548 cerebral aneurysms treated by endovascular coiling, 143 patients with 148 small cerebral aneurysms underwent endovascular coiling. After March 2013, coiling with Nano™ coils was performed on 45 small cerebral aneurysms (30.4%).

Results

There were no significant differences in the size and locations of the cerebral aneurysms, the age of the patients, and the procedural modalities between the two groups. The proportion of the coil (≤ 1.5 mm) of the group treated with Nano™ coils (53.6%) was higher than the proportion of the coil (≤ 1.5 mm) of the group treated without Nano™ coils (14.7%) with statistical significance (p < 0.001). The packing density of the group treated with Nano™ coils (31.3 ± 9.69%) was higher than the packing density of the group treated without Nano™ coils (29.49 ± 7.84%), although the difference was not significant. Procedural complications developed in 3 lesions (2 thromboembolisms and 1 carotid dissection) (2.0%). Treatment-related transient neurological deficits due to thromboembolism developed in 1 lesion, which had not been treated with Nano™ coils. There was no treatment-related permanent morbidity or mortality in either of the groups.

Conclusion

In our series, the small cerebral aneurysms treated with Nano™ coils showed more packing density with no additive procedural risk or difficulty.

Fate of Coiled Aneurysms with Minor Recanalization at 6 Months: Rate of Progression to Further Recanalization and Related Risk Factors

BACKGROUND AND PURPOSE

Minor recanalization in coiled aneurysms may remain stable with time or may progress to major recanalization. Our aim was to monitor the aneurysms displaying minor recanalization in imaging studies at 6 months, gauging major recanalization rates and related risk factors through extended follow-up.

MATERIALS AND METHODS

Sixty-five aneurysms (in 65 patients) showing minor recanalization in follow-up imaging at 6 months were reviewed retrospectively. Medical records and radiologic data accruing during extended monitoring (mean, 24.8 ± 8.2 months) were assessed. Univariate and multivariate analyses were conducted to identify risk factors for progression from minor-to-major recanalization.

RESULTS

Progression to major recanalization was observed in 24 (36.9%) of the initially qualifying aneurysms during a follow-up of 112.5 aneurysm-years, for an annual rate of 17.84% per aneurysm-year. Progression was determined chronologically as follows: 14 (58.3%) at 6 months, 8 (33.3%) at 18 months, and 2 (8.4%) at 30 months. Stent deployment significantly decreased the occurrence of major recanalization (OR = 0.22, P = .03), whereas antiplatelet therapy (OR = 0.82, P = .75), posterior location (OR = 0.24, P = .20), and second coiling for recanalized aneurysms (OR = 0.96, P = .96) were unrelated.

CONCLUSIONS

Our analysis determined a 36.9% rate of major recanalization during a follow-up of 112.5 aneurysm-years in coiled aneurysms showing minor recanalization at 6 months. Stent deployment alone conferred a protective effect, preventing further recanalization without additional treatment. Given the fair probability of late major recanalization, aneurysms showing minor recanalization at 6 months should be monitored diligently, particularly in the absence of stent placement.

Predictor and Prognosis of Procedural Rupture during Coil Embolization for Unruptured Intracranial Aneurysm

Objective

The objectives of this study was to determine the incidence and outcomes of procedural rupture (PR) during coil embolization of unruptured intracranial aneurysm (UIA) and to explore potential risk factors.

Methods

This retrospective study evaluated 1038 patients treated with coil embolization between January 2001 and May 2013 in a single tertiary medical institute. PR was defined as evidence of rupture during coil embolization or post procedural imaging. The patient's medical records were reviewed including procedure description, image findings and clinical outcomes.

Results

Twelve of 1038 (1.1%) patients showed PR. Points and time of rupture were parent artery rupture during stent delivery (n=2), aneurysm rupture during filling stage (n=9) and unknown (n=1). Two parent artery rupture and one aneurysm neck rupture showed poor clinical outcomes [modified Rankin Scale (mRs) >2] Nine aneurysm dome rupture cases showed favorable outcomes (mRS ≤2). Location (anterior cerebral artery) of aneurysm was associated with high procedural rupture rate (p<0.05).

Conclusion

The clinical course of a patientwith procedural aneurysm rupture during filling stage seemed benign. Parent artery and aneurysm neck rupture seemed relatively urgent, serious and life threatening. Although the permanent morbidity rate was low, clinicians should pay attention to prevent PR, especially when confronting the anterior cerebral artery aneurysm.

Extended monitoring of coiled aneurysms completely occluded at 6-month follow-up: late recanalization rate and related risk factors

OBJECTIVES

To estimate long-term durability in coiled aneurysms completely occluded at 6-month follow-up imaging, focusing on late recanalization rate and the risk factors involved.

METHODS

A cohort of 620 patients harbouring 698 completely occluded coiled aneurysms at 6-month follow-up was subjected to extended monitoring (mean, 24.5 ± 7.9 months). Cumulative recanalization rate and related risk factors were analysed using Cox proportional hazards regression and Kaplan-Meier product-limit estimator.

RESULTS

Forty-three aneurysms (6.2 %) occluded completely at 6-months displayed recanalization (3.02 % per aneurysm-year) during continued surveillance (1425.5 aneurysm-years), with 26 (60.5 %) surfacing in another 6 months, 15 (34.9 %) within 18 months and 2 (4.6 %) within 30 months. Cumulative survival rates without recanalization were significantly lower in subjects with aneurysms >7 mm (p = 0.014), with bifurcation aneurysms (p = 0.009) and with subarachnoid haemorrhage (SAH) at presentation (p < 0.001). Multivariate analysis indicated that aneurysms >7 mm (HR = 2.37, p = 0.02) and bifurcation aneurysms (HR = 2.70, p = 0.03) were significant factors in late recanalization, whereas a link with SAH at presentation was marginal (HR = 1.92, p = 0.06) and stent placement fell short of statistical significance (HR = 0.47; p = 0.12).

CONCLUSION

Most (93.8 %) coiled aneurysms showing complete occlusion at 6 months post-procedure were stable in long-term monitoring. However, aneurysms >7 mm and bifurcation aneurysms were predisposed to late recanalization.

KEY POINTS

• Most coiled aneurysms showing complete occlusion at 6 months were stable. • Forty-three aneurysms (6.2 %) occluded completely at 6-month follow-up displayed late recanalization. • Late recanalization rate was 3.02 % per aneurysm-year during follow-up of 1425.5 aneurysm-years. • Aneurysms over 7 mm and bifurcation aneurysms were predisposed to late recanalization.

The significant impact of framing coils on long-term outcomes in endovascular coiling for intracranial aneurysms: how to select an appropriate framing coil

OBJECTIVE The importance of a framing coil (FC)-the first coil inserted into an aneurysm during endovascular coiling, also called a lead coil or a first coil-is recognized, but its impact on long-term outcomes, including recanalization and retreatment, is not well established. The purposes of this study were to test the hypothesis that the FC is a significant factor for aneurysmal recurrence and to provide some insights on appropriate FC selection. METHODS The authors retrospectively reviewed endovascular coiling for 280 unruptured intracranial aneurysms and gathered data on age, sex, aneurysm location, aneurysm morphology, maximal size, neck width, adjunctive techniques, recanalization, retreatment, follow-up periods, total volume packing density (VPD), volume packing density of the FC, and framing coil percentage (FCP; the percentage of FC volume in total coil volume) to clarify the associated factors for aneurysmal recurrence. RESULTS Of 236 aneurysms included in this study, 33 (14.0%) had recanalization, and 18 (7.6%) needed retreatment during a mean follow-up period of 37.7 ± 16.1 months. In multivariate analysis, aneurysm size (odds ratio [OR] = 1.29, p < 0.001), FCP < 32% (OR 3.54, p = 0.009), and VPD < 25% (OR 2.96, p = 0.015) were significantly associated with recanalization, while aneurysm size (OR 1.25, p < 0.001) and FCP < 32% (OR 6.91, p = 0.017) were significant predictors of retreatment. VPD as a continuous value or VPD with any cutoff value could not predict retreatment with statistical significance in multivariate analysis. CONCLUSIONS FCP, which is equal to the FC volume as a percentage of the total coil volume and is unaffected by the morphology of the aneurysm or the measurement error in aneurysm length, width, or height, is a novel predictor of recanalization and retreatment and is more significantly predictive of retreatment than VPD. To select FCs large enough to meet the condition of FCP ≥ 32% is a potential relevant factor for better long-term outcomes. These findings support our hypothesis that the FC is a significant factor for aneurysmal recurrence.

Endovascular coiling of small intracranial aneurysms using a very soft bare platinum coil: A comparison of the packing performance of new and old HyperSoft® helical coils

AIMS

Soft and small coils are known to be appropriate for the treatment of small aneurysms. The purpose of this study was to determine whether the new HyperSoft® helical coil, which is softer and smaller than its predecessors, has any effect on the packing performance in a matched-pair study with an old HyperSoft® helical coil.

MATERIALS AND METHODS

Thirty-six consecutive patients harboring 43 cerebral aneurysms treated with new HyperSofts were included in this study. Forty-one aneurysms treated with old HyperSofts were identified from our database as matched controls based on similar volumes and locations. Packing attenuation, adverse events during the procedures, and angiographic occlusions were observed and compared between the two groups.

RESULTS

The mean packing density was significantly higher in the new HyperSoft® group compared to the control group (35.5% vs. 26.9%), and a larger proportion of the aneurysms embolized with the 1.5 mm size coil, which has higher packing density. There was no difference in immediate and midterm angiographic outcomes. There was no difference in the rate of intraprocedural perforation, but there was no intraprocedural rupture related to the 1.5 mm coil.

CONCLUSIONS

The use of new HyperSoft® helical coils allows higher packing density comparable with the old technology. New HyperSoft® coils, especially those with 1.5 mm loop diameter, can be expected to fill smaller residual spaces in small aneurysms and may be helpful in preventing recanalization.

Effect of hemodynamics on outcome of subtotally occluded paraclinoid aneurysms after stent-assisted coil embolization

BACKGROUND

Endovascular treatment of paraclinoid aneurysms is preferred in clinical practice. Flow alterations caused by stents and coils may affect treatment outcome.

OBJECTIVE

To assess hemodynamic changes following stent-assisted coil embolization (SACE) in subtotally embolized paraclinoid aneurysms with residual necks that were predisposed to recanalization.

METHODS

We studied 27 paraclinoid aneurysms (seven recanalized and 20 stable) treated with coils and Enterprise stents. Computational fluid dynamic simulations were performed on patient-specific aneurysm geometries using virtual stenting and porous media technology.

RESULTS

After stent placement in 27 cases, aneurysm flow velocity decreased significantly, the reduction gradually increasing from the neck plane (11.9%), to the residual neck (12.3%), to the aneurysm dome (16.3%). Subsequent coil embolization was performed after stent placement and the hemodynamic factors decreased further and significantly at all aneurysm regions except the neck plane. In a comparison of recanalized and stable cases, univariate analysis showed no significant differences in any parameter before treatment. After stent-assisted coiling, only the reduction in area-averaged velocity at the neck plane differed significantly between recanalized (8.1%) and stable cases (20.5%) (p=0.016).

CONCLUSIONS

Aneurysm flow velocity can be significantly decreased by stent placement and coil embolization. However, hemodynamics at the aneurysm neck plane is less sensitive to coils. Significant reduction in flow velocity at the neck plane may be an important factor in preventing recanalization of paraclinoid aneurysms after subtotal SACE.

Volume versus standard coils in the treatment of intracranial aneurysms

BACKGROUND

Volume coils were developed to improve occlusion rates of intracranial aneurysms. Previous studies have shown increased packing density and comparable occlusion rates, but subgroup analyses of aneurysm size have not been carried out.

OBJECTIVE

To evaluate the safety and efficacy of the Penumbra Coil 400 (PC400) system in treating intracranial aneurysms compared with standard diameter coils.

METHODS

A monocentric retrospective case review of 260 aneurysms in 233 patients was carried out. In 37 aneurysms the PC400 system was used, while 223 aneurysms were treated with conventional coils. Previously treated aneurysms and aneurysms treated with flow diverters were excluded. Aneurysm and procedure characteristics, packing density, postprocedural and follow-up occlusion grades as well as coil compaction were evaluated.

RESULTS

Aneurysms treated with PC400 coils had higher volume (218.9 vs 47.1 mm(3), p<0.001), wider necks (3.0 vs 2.5 mm, p=0.005), and greater dome/neck ratio (2.0 vs 1.6, p=0.001) in comparison with aneurysms treated with conventional coils. Compared with controls, in the PC400 group we achieved higher packing densities (43.2% vs 34.4%, p<0.001; in aneurysms ≥7 mm 42.2% vs 27.8%, p<0.001). On follow-up angiography we observed less coil compaction (23.8% vs 64.3%, p=0.003) and less aneurysm recurrence (14.3% vs 40.5%, p=0.046) in aneurysms ≥7 mm when using the PC400 system.

CONCLUSIONS

Use of the PC400 system as opposed to conventional coils suggests that the PC400 system is safe and effective in treating intracranial aneurysms. Despite having been applied in a potentially more difficult-to-treat group, the use of PC400 was associated with less coil compaction and aneurysm recurrence in aneurysms ≥7 mm.

HydroCoils Are Associated with Lower Angiographic Recurrence Rates Than Are Bare Platinum Coils in Treatment of "Difficult-to-Treat" Aneurysms: A Post Hoc Subgroup Analysis of the HELPS Trial

BACKGROUND AND PURPOSE

The HydroCoil Endovascular Aneurysm Occlusion and Packing Study was a randomized controlled trial that compared HydroCoils to bare platinum coils. Using data from this trial, we performed a subgroup analysis of angiographic and clinical outcomes of patients with "difficult-to-treat" aneurysms, defined as irregularly shaped and/or having a dome-to-neck ratio of <1.5.

MATERIALS AND METHODS

Separate subgroup analyses comparing outcomes of treatment with HydroCoils to that of bare platinum coils were performed for the following: 1) irregularly shaped aneurysms, 2) regularly shaped aneurysms, 3) aneurysms with a dome-to-neck ratio of <1.5, and 4) aneurysms with a dome-to-neck ratio of ≥1.5. For each subgroup analysis, the following outcomes were studied at the last follow-up (3-18 months): 1) any recurrence, 2) major recurrence, 3) re-treatment, and 4) an mRS score of ≤2. Multivariate logistic regression analysis was performed to determine if the HydroCoil was independently associated with improved outcomes in these subgroups.

RESULTS

Among the patients with an irregularly shaped aneurysm, the HydroCoil was associated with lower major recurrence rates than the bare platinum coils (17 of 66 [26%] vs 30 of 69 [44%], respectively; P = .046). Among the patients with an aneurysm with a small dome-to-neck ratio, the HydroCoil was associated with lower major recurrence rates than the bare platinum coils (18 of 73 [24.7%] vs 32 of 76 [42.1%], respectively; P = .02). No difference in major recurrence was seen between HydroCoils and bare platinum coils for regularly shaped aneurysms (42 of 152 [27.6%] vs 52 of 162 [32.1%], respectively; P = .39) or aneurysms with a large dome-to-neck ratio (41 of 145 [28.3%] vs 50 of 155 [32.3%], respectively; P = .53).

CONCLUSIONS

This unplanned post hoc subgroup analysis found that HydroCoils are associated with improved angiographic outcomes in the treatment of irregularly shaped aneurysms and aneurysms with a dome-to-neck ratio of <1.5. Because this was a post hoc analysis, these results are not reliable and absolutely should not alter clinical practice but, rather, may inform the design of future randomized controlled trials.

Finite element modeling of endovascular coiling and flow diversion enables hemodynamic prediction of complex treatment strategies for intracranial aneurysm

Endovascular interventions using coil embolization and flow diversion are becoming the mainstream treatment for intracranial aneurysms (IAs). To help assess the effect of intervention strategies on aneurysm hemodynamics and treatment outcome, we have developed a finite-element-method (FEM)-based technique for coil deployment along with our HiFiVS technique for flow diverter (FD) deployment in patient-specific IAs. We tested four clinical intervention strategies: coiling (1-8 coils), single FD, FD with adjunctive coils (1-8 coils), and overlapping FDs. By evaluating post-treatment hemodynamics using computational fluid dynamics (CFD), we compared the flow-modification performance of these strategies. Results show that a single FD provides more reduction in inflow rate than low packing density (PD) coiling, but less reduction in average velocity inside the aneurysm. Adjunctive coils add no additional reduction of inflow rate beyond a single FD until coil PD exceeds 11%. This suggests that the main role of FDs is to divert inflow, while that of coils is to create stasis in the aneurysm. Overlapping FDs decreases inflow rate, average velocity, and average wall shear stress (WSS) in the aneurysm sac, but adding a third FD produces minimal additional reduction. In conclusion, our FEM-based techniques for virtual coiling and flow diversion enable recapitulation of complex endovascular intervention strategies and detailed hemodynamics to identify hemodynamic factors that affect treatment outcome.

Implantation of pipeline flow-diverting stents reduces aneurysm inflow without relevantly affecting static intra-aneurysmal pressure

BACKGROUND

Flow-diverting stent (FDS) implantation is an endovascular treatment option for intracranial aneurysms. However, little is known about the hemodynamic effects.

OBJECTIVE

To assess the effect of stent compression on FDS porosity, to evaluate the influence of single and overlapping implantation of FDS on intra-aneurysmal flow profiles, and to correlate stent porosity with changes in static mean intra-aneurysmal pressure.

METHODS

Intra-aneurysmal time-density curves were recorded in a pulsatile in vitro flow model before and after implantation of FDSs (Pipeline Embolization Device; ev3) in 7 different types of aneurysm models. Reductions in the maximum contrast inflow and time to maximum intra-aneurysmal contrast were calculated. Micro--computed tomography was performed, and compression-related FDS porosity was measured. The influence of FDS placement on mean static intra-aneurysmal pressure was measured.

RESULTS

FDS compression resulted in an almost linear reduction in stent porosity. Stent porosity (struts per 1 mm) correlated significantly with the reduction of aneurysm contrast inflow (R = 0.81, P < .001) and delay until maximum contrast (R = 0.34, P = .001). Circulating intra-aneurysmal high-velocity flow was terminated in all sidewall models after implantation of a single stent. Superimposition of 2 stents reduced maximum intra-aneurysmal contrast by 69.1 ± 3.1% (mean ± SD) in narrow-necked sidewall aneurysm models, whereas no substantial reduction in maximum intra-aneurysmal contrast was observed in wide-necked sidewall aneurysm models. Intra-aneurysmal mean static pressure did not correlate with FDS porosity or number of implanted stents.

CONCLUSION

Implantation of FDS effectively reduces aneurysm inflow in a porosity-dependent way without relevantly affecting static mean intra-aneurysmal pressure.

ABBREVIATIONS

FDS, flow-diverting stentMAP, mean arterial pressurePED, Pipeline Embolization Device.

Aneurysm permeability following coil embolization: packing density and coil distribution

Background

Rates of durable aneurysm occlusion following coil embolization vary widely, and a better understanding of coil mass mechanics is desired. The goal of this study is to evaluate the impact of packing density and coil uniformity on aneurysm permeability.

Methods

Aneurysm models were coiled using either Guglielmi detachable coils or Target coils. The permeability was assessed by taking the ratio of microspheres passing through the coil mass to those in the working fluid. Aneurysms containing coil masses were sectioned for image analysis to determine surface area fraction and coil uniformity.

Results

All aneurysms were coiled to a packing density of at least 27%. Packing density, surface area fraction of the dome and neck, and uniformity of the dome were significantly correlated (p<0.05). Hence, multivariate principal components-based partial least squares regression models were used to predict permeability. Similar loading vectors were obtained for packing and uniformity measures. Coil mass permeability was modeled better with the inclusion of packing and uniformity measures of the dome (r²=0.73) than with packing density alone (r²=0.45). The analysis indicates the importance of including a uniformity measure for coil distribution in the dome along with packing measures.

Conclusions

A densely packed aneurysm with a high degree of coil mass uniformity will reduce permeability.

Hemodynamic impact of cerebral aneurysm endovascular treatment devices: coils and flow diverters

Coils and flow diverters or stents are devices successfully used to treat cerebral aneurysms. Treatment aims to reduce intra-aneurysmal flow, thereby separating the aneurysmal sac from the blood circulation. The focus and this manuscript combining literature review and our original research is an analysis of changes in aneurysmal hemodynamics caused by endovascular treatment devices. Knowledge of post-treatment hemodynamics is a path to successful long-term treatment. Summarizing findings on hemodynamic impact of treatment devices, we conclude: coiling and stenting do not affect post-treatment intra-aneurysmal pressure, but significantly alter aneurysmal hemodynamics through flow reduction and a change in flow structure. The impact of treatment devices on aneurysmal flow depends, however, on a set of parameters including device geometry, course of placement, parent vessel and aneurysm geometry.

Intrasaccular flow-diversion for treatment of intracranial aneurysms: the Woven EndoBridge

Endovascular approach is now the first option for the treatment of most intracranial aneurysms (IA). However, remaining limitations are the suboptimal stability of aneurysm occlusion and the treatment of complex IA. The use of conventional and flow diverter stents has partially addressed these limitations. Nevertheless, as intraluminal devices, stents require aggressive antiplatelet therapy and are associated with higher thromboembolic (TE) complication rates. Intrasaccular flow disrupters (IFD) are newly developed braided-wire devices designed to achieve flow disruption at the neck without placing material in the parent vessel and without the need of antiplatelet therapy. First clinical series have shown promising anatomical and clinical results. Our purpose is to describe the available IFD and to review the literature about their efficacy, safety, limitations, and developments.