Computation of the change in length of a braided device when deployed in realistic vessel models

Verification of software-based preoperative simulation of flow diverters in clinical cases

OBJECTIVE

The authors sought to verify the use of a preoperative simulation software for the treatment of intracranial aneurysms using flow diverters (FDs) based on three-dimensional rotational angiography (3DRA) data.

METHODS

Based on 3DRA data, the preoperative simulation software (UKNOW) was used to simulate the deployment of virtual FDs. The length and dimensions of virtual and real devices were compared. The deployment plan recommended by the UKNOW software was preliminarily used to complete implantations in the real world. During the experiment, experienced neurointerventional experts were responsible for supervising and judging information such as the length, dimension, and deployment location of the FDs.

RESULTS

This study retrospectively analyzed the data of 29 patients who received FD treatment. There was no statistical difference between the length of the real device and the virtual device (p = 0.6). The dimensions of FDs recommended by the software were consistent with the dimensions used in 24 out of the 29 real cases. In four of the remaining five cases, neurointerventional experts found that the FD dimensions recommended by the software were superior to those were actually used. Thus, the accuracy rate for FD dimension recommendations by the UKNOW software was 96.6% (28/29). Procedures performed in five cases using deployment plans recommended by the UKNOW software all achieved good postoperative results; the deployment positions of the device were reasonable, and all devices showed good wall adherence.

CONCLUSIONS

UKNOW software could accurately simulate the length and deployment position of the real FDs and provide suitable device dimensions.

PREDICT: Precise deployment of Silk Vista Baby in confined territory: A technical note

Flow diverters (FD) have become increasingly useful in treating complex intracranial aneurysms, particularly wide-necked and recurrent aneurysms. Their use has progressively expanded to smaller vessels beyond the circle of Willis (CoW), and Silk Vista Baby (SVB) is one such low-profile FD which stands out because of deliverability through a 0.017″ microcatheter and smoother navigability. Precise deployment of SVB, specifically, the proximal end, can be challenging in certain anatomical locations when the proximal landing zone is very short, limited by vessel bifurcation or important branches arising from the artery or its geometry. We present our series to describe our technique and rule to 'PREDICT' the final deployment of SVB in real time, and discuss the nuances, exceptions and bail-out strategies. Using this technique, we were able to precisely deploy SVB in distal intracranial vessels with a mean proximal landing zone as short as 2.6 mm in 80% instances, requiring bail-out strategies in only 20% cases. This rule can be reliably followed in treating complex intracranial aneurysms with SVB FD within a confined territory, until validated software-based real-time planning tools are developed.

Simulation of intra-saccular devices for pre-operative device size selection: Method and validation for sizing and porosity simulation

Intra-saccular devices (ID) are novel braided devices used for complex intracranial aneurysms treatment. Treatment success is associated with correct device size selection. A technique that predicts the ID size within the aneurysm before intervention will provide a powerful computational tool to aid the interventionist during device selection. We present a method to calculate the device's final height, radial expansion and porosity within the patient's anatomy, which allows assessing different device sizes before treatment takes place. The proposed sizing technique was tested in-vitro and in real patient's geometries obtained from 3DRA angiographic images of 8 unruptured aneurysms previously treated with IDs. The obtained simulated height was compared to the real height, with a mean error of less than 0.28 mm (±0.44). The porosity calculation method was tested in-vitro with an error of 0.02 (±0.022). The results of both sizing and porosity experiments resemble well measures from real patients. This methodology could be used before treatment to provide the interventionist with additional information that allows selecting the device that best fits the patient's aneurysm to be treated.

Cerebral Aneurysm Occlusion at 12-Month Follow-Up After Flow-Diverter Treatment: Statistical Modeling for V&V With Real-World Data

Background: Flow-Diverter (FD) porosity has been pointed as a critical factor in the occlusion of cerebral aneurysms after treatment.

Objective: Verification and Validation of computational models in terms of predictive capacity, relating FD porosity and occlusion after cerebral aneurysms treatment.

Methods: Sixty-four aneurysms, with pre-treatment and follow-up images, were considered. Patient demographics and aneurysm morphological information were collected. The computational simulation provided by ANKYRAS provided FD porosity, expansion, and mesh angle. FD occlusion was assessed and recorded from follow-up images. Multiple regression Logit and analysis of covariance (ANCOVA) models were used to model the data with both categorical and continuous models.

Results: Occlusion of the aneurysm after 12 months was affected by aneurysm morphology but not by FD mesh morphology. A Time-To-Occlusion (TTO) of 6.92 months on average was observed with an SE of 0.24 months in the aneurysm population surveyed. TTO was estimated with statistical significance from the resulting model for the data examined and was capable of explaining 92% of the data variation.

Conclusions: Porosity was found to have the most correction power when assessing TTO, proving its importance in the process of aneurysm occlusion. Still, further Verification and Validation (V&V) of treatment simulation in more extensive, multi-center, and randomized databases is required.

Review of current intracranial aneurysm flow diversion technology and clinical use

Endovascular treatment of intracranial aneurysms (IAs) has evolved considerably over the past decades. The technological advances have been driven by the experience that coils fail to completely exclude all IAs from the blood circulation, the need to treat the diseased parent vessel segment leading to the aneurysm formation, and expansion of endovascular therapy to treat more complex IAs. Stents were initially developed to support the placement of coils inside wide neck aneurysms. However, early work on stent-like tubular braided structure led to a more sophisticated construct that then later was coined as a flow diverter (FD) and found its way into clinical application. Although FDs were initially used to treat wide-neck large and giant internal carotid artery aneurysms only amenable to surgical trap with or without a bypass or endovascular vessel sacrifice, its use in other types of IAs and cerebrovascular pathology promptly followed. Lately, we have witnessed an explosion in the application of FDs and subsequently their modifications leading to their ubiquitous use in endovascular therapy. In this review we aim to compile the available FD technology, evaluate the devices' peculiarities from the authors' perspective, and analyze the current literature to support initial and expanded indications, recognizing that this may be outdated soon.

Deployment of flow diverter devices: prediction of foreshortening and validation of the simulation in 18 clinical cases

PURPOSE

Flow diverter (FD) devices show severe shortening during deployment in dependency of the vessel geometry. Valid information regarding the geometry of the targeted vessel is therefore mandatory for correct device selection, and to avoid complications. But the geometry of diseased tortuous intracranial vessels cannot be measured accurately with standard methods. The goal of this study is to prove the accuracy of a novel virtual stenting method in prediction of the behavior of a FD in an individual vessel geometry.

METHODS

We applied a virtual stenting method on angiographic 3D imaging data of the specific vasculature of patients, who underwent FD treatment. The planning tool analyzes the local vessel morphology and deploys the FD virtually. We measured in 18 cases the difference between simulated FD length and real FD length after treatment in a landmark-based registration of pre-/post-interventional 3D angiographic datasets.

RESULTS

The mean value of length deviation of the virtual FD was 2.2 mm (SD ± 1.9 mm) equaling 9.5% (SD ± 8.2%). Underestimated cases present lower deviations compared with overestimated FDs. Flow diverter cases with a nominal device length of 20 mm had the highest prediction accuracy.

CONCLUSION

The results suggest that the virtual stenting method used in this study is capable of predicting FD length with a clinically sufficient accuracy in advance and could therefore be a helpful tool in intervention planning. Imaging data of high quality are mandatory, while processing and manipulation of the FD during the intervention may impact the accuracy.

Comparison of Pipeline Embolization Device Sizing Based on Conventional 2D Measurements and Virtual Simulation Using the Sim&Size Software: An Agreement Study

BACKGROUND AND PURPOSE

The Sim&Size software simulates case-specific intraluminal Pipeline Embolization Device behavior, wall apposition, and device length in real-time on the basis of rotational angiography DICOM data. The purpose of this multicenter study was to evaluate whether preimplantation device simulation with the Sim&Size software results in selection of different device dimensions than manual sizing.

MATERIALS AND METHODS

In a multicenter cohort of 74 patients undergoing aneurysm treatment with the Pipeline Embolization Device, we compared apparent optimal device dimensions determined by neurointerventionalists with considerable Pipeline Embolization Device experience based on manual 2D measurements taken from rotational angiography with computed optimal dimensions determined by Sim&Size experts blinded to the neurointerventionalists' decision. Agreement between manually determined and computed optimal dimensions was evaluated with the Cohen κ. The significance of the difference was analyzed with the Wilcoxon signed rank test.

RESULTS

The agreement index between manual selection and computed optimal dimensions was low (κ for diameter = 0.219; κ for length = 0.149, P < .01). Computed optimal device lengths were significantly shorter (median, 14 versus 16 mm, T = 402, r = -0.28, P < .01). No significant difference was observed for device diameters.

CONCLUSIONS

Low agreement between manually determined and computed optimal device dimensions is not proof, per se, that virtual simulation performs better than manual selection. Nevertheless, it ultimately reflects the potential for optimization of the device-sizing process, and use of the Sim&Size software reduces, in particular, device length. Nevertheless, further evaluation is required to clarify the impact of device-dimension modifications on outcome.

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.

Early Results in Flow Diverter Sizing by Computational Simulation: Quantification of Size Change and Simulation Error Assessment

BACKGROUND

Sizing of flow diverters (FDs) stent in the treatment of intracranial aneurysms is a challenging task due to the change of stent length after implantation.

OBJECTIVE

To quantify the size change and assess the error in length prediction in 82 simulated FD deployments.

METHODS

Eighty-two consecutive patients treated with FDs were retrospectively analyzed. Implanted FD length was measured from angiographic images and compared to the nominal sizes of the implanted device. Length change was obtained by subtracting the nominal length from the real length and dividing by the nominal length. Implanted devices were simulated on 3-dimensional models of each patient. Simulation error was obtained by subtracting real length from simulated length and dividing by the real length of the FD. Subanalysis was done using ANOVA. Statistical significance was set to P < .05, and bootstrap resampling was used.

RESULTS

When assessing the length change of the FD after implantation, changes of 30% in average and up to 80% with reference to the nominal length of the device were observed. The simulation results showed a lower error of 3.52% in average with a maximum of 30%. Paired t-test showed nonsignificant differences between measured and real length (P = .07, with the mean of differences at 0.45 mm, 95% confidence interval [-0.950 0.038]).

CONCLUSION

Nominal length is not an accurate sizing metric when choosing the size of an FD irrespective of the brand and manufacturer. Good estimation of the final length of the stent after deployment as expressed by an error of 3.5% in average.