Aneurysm Phantom Research Articles

Characterization of Conventional Endovascular Devices in Treatment of Abdominal Aortic Aneurysms

Abstract Abdominal aortic aneurysms (AAA) are often repaired through an endovascular approach known as endovascular aneurysm repair (EVAR). The success and duration of these challenging procedures are primarily attributable to the accuracy and reliability of navigating corresponding interventional devices. This study investigates the performance of conventional nonsteerable and steerable catheters in EVAR procedures, focusing on two primary metrics: reachable workspace and gate cannulation success. We developed two abdominal aortic aneurysm (AAA) phantoms using patient CT images for our experiments. Under X-ray fluoroscopy guidance, the reachable workspace was quantified, and gate cannulation success rates, cannulation time, and fluoroscopy times were recorded for both nonsteerable and steerable catheters and were compared. We were unable to observe statistically significant differences between the two catheter types in overall cannulation success rates or fluoroscopy time. However, in challenging anatomical scenarios (particularly a more challenging gate location), the steerable catheter showed statistically significant advantages in success rates and cannulation times. While there were no statistical differences in reachable workspace between nonsteerable and steerable catheters when considering the whole aneurysm, segmented analysis showed that the steerable catheter performed better in the central region, and nonsteerable catheters performed better in the peripheral region. This study provides a systematic method for quantifying the performance of endovascular devices. The findings suggest that while steerable catheters may offer advantages in complex anatomical conditions, nonsteerable catheters are preferable in peripheral areas of the aneurysm. These insights can inform catheter selection in EVAR, potentially influencing device design and clinical practice.

Experimental study using phantom models of cerebral aneurysms and 4D-DSA to measure blood flow on 3D-color-coded images.

The current 3D-iFlow application can only measure the arrival time of contrast media through intensity values. If the flow rate could be estimated by 3D-iFlow, patient-specific hemodynamics could be determined within the scope of normal diagnostic management, eliminating the need for additional resources for blood flow rate estimation. The aim of this study is to develop and validate a method for measuring the flow rate by data obtained from 3D-iFlow images - a prototype application in Four-dimensional digital subtraction angiography (4D-DSA). Using phantom model and experimental circuit with circulating glycerin solution, an equation for the relationship between contrast media intensity and flow rate was developed. Applying the equation to the aneurysm phantom models, the derived flow rate was evaluated. The average errors between the derived flow rate and setting flow rate became larger when the glycerin flow and the X-rays from the X-ray tube of the angiography system were parallel to each other or when the measurement point included overlaps with other contrast enhanced areas. Although the error increases dependent on the imaging direction and overlap of contrast enhanced area, the developed equation can estimate the flow rate using the image intensity value measured on 3D-iFlow based on 4D-DSA.

Application of 3D printing to create an in vitro aneurysm rupture model.

Currently available benchtop (in vitro) aneurysm models are inadequate for testing the efficacy of endovascular device treatments. Specifically, current models do not represent the mechanical instability of giant aneurysms (defined as aneurysms with 25 mm in height or width) and do not predictably rupture under simulated physiological conditions. Hence, in vitro aneurysm models with biomechanically relevant material properties and a predictable rupture timeframe are needed to accurately assess the efficacy of new medical device treatment options. Understanding the material properties of an aneurysm (e.g., shear and compression modulus) as it approaches rupture is a crucial step toward creating a pathologically relevant and sophisticated in vitro aneurysm rupture model. We investigated the change in material properties of a blood vessel, via enzymatic treatment, to simulate the degradation of an aneurysm wall and used this information to create a sophisticated aneurysm rupture model using the latest in additive manufacturing technologies (3D printing) with tissue-like materials. Mechanical properties (shear and compression modulus) of swine carotid vessels were evaluated before and after incubation with collagenase D enzyme (30 min at 37°C) to simulate the effect of biochemical activity on aneurysm wall approaching rupture compared to control vessels (untreated). Mechanical strength of a soft and flexible 3D-printed material (VCA-A30: 30 shore A hardness) was tested for comparison to these arterial vessels. This material was then used to create spherical shaped, giant-sized (25-mm diameter) aneurysm phantoms and were run under neurovascular pressures (120/80 ± 5 mmHg), beats per minute (BPM = 70) and flows representing the middle cerebral artery [MCA: 142.67 (±20.13) mL/min] using a blood analog [3.6 (±0.4) cP viscosity] with non-Newtonian shear-thinning properties. The shear modulus of swine carotid vessel before treatment was 12.2 (±2.7) KPa and compression modulus was 663.5 (±111.6) KPa. After enzymatic treatment by collagenase D, shear modulus of animal tissues reduced by 33% (p-value = .039) while compression modulus remained statistically unchanged (p-value = .615). Control group (untreated vessels) showed minimal reduction (13%, p-value = .226) in shear modulus and 78% increase (p-value = .034) in compression modulus. The shear modulus of the 3D-printed material was 228.59 (±24.82) KPa while its compression modulus was 668.90 (±13.16) KPa. This material was used to prototype a sophisticated in vitro giant aneurysm rupture model. When subjected to physiological pressures and flow rates, the untreated models consistently ruptured at ~12 min. These results indicate that aneurysm rupture can be recreated consistently in a benchtop in vitro model, utilizing the latest 3D-printed materials, connected to a physiologically relevant programmable pump. Further studies will investigate the optimization of various aneurysm dome thickness regions within the aneurysm, with tunable rupture times for comparison of aneurysm device deployment and benchtop controls based on the measurable effects of pressure and flow changes within the aneurysm models. These optimized in vitro rupture models could ultimately be used to test the efficacy of device treatment options and rupture risk by quantifying specific device rupture times and aneurysm rupture position.

Evaluation of aneurysm flow divertor (stent) treatment using multi-angled 1000 fps High-Speed Angiography (HSA) and Optical Flow (OF).

Understanding detailed hemodynamics is critical in the treatment of aneurysms and other vascular diseases; however, traditional digital subtraction angiography (DSA) does not provide detailed quantitative flow information. Instead, 1000 fps High-Speed Angiography (HSA) can be used for high-temporal visualization and evaluation of detailed blood flow patterns and velocity distributions. In the treatment of aneurysms, flow diverter expansion and positioning play a critical role in affecting the hemodynamics and optimal patient outcomes. Patient-specific aneurysm phantom imaging was done with a CdTe photon-counting detector (Aries, Varex). Treatment was done with a Pipeline Flex Embolization Device on a 3D-printed fusiform aneurysm phantom. The untreated aneurysm and two treatment stent expansions and positions were imaged, and velocity calculations were generated using Optical Flow (OF). Pre- and post-treatment images were then compared between different HSA image sequences and evaluated using OF with different stent positions. Differences in flow patterns due to changes in stent placement characteristics were identified and quantified with OF velocimetry. The velocity results within the aneurysm post-treatment showed significant flow reduction. Differences in stent placement result in substantial changes in velocities. The peak velocities found in the aneurysm dome show a reduction with the widened stent placement compared to the narrowed placement and both are reduced compared to the untreated aneurysm. The stent placements were compared quantitatively with the adjusted widened stent clearly better diverting the flow away from the aneurysm with decreased velocity in the aneurysm dome compared to both the narrowed stent placement and the untreated aneurysm. Providing this information in-clinic can help improve treatment and patient outcomes.

Microwave Imaging System Based on Signal Analysis in a Planar Environment for Detection of Abdominal Aortic Aneurysms.

A proof-of-concept of a microwave imaging system for the fast detection of abdominal aortic aneurysms is shown. This experimental technology seeks to overcome the factors hampering the fast screening for these aneurysms with the usual equipment, such as high cost, long-time operation or hazardous exposure to chemical substances. The hardware system is composed of 16 twin antennas mastered by a microcontroller through a switching network, which connects the antennas to the measurement instrument for sequential measurement. The software system is run by a computer, mastering the whole system, automatizing the measurement process and running the signal processing and medical image generation algorithms. Two image generation algorithms are tested: Delay-and-Sum (DAS) and Improved Delay-and-Sum (IDAS). Own-modified versions of these algorithms adapted to the requirements of our system are proposed. The system is carefully calibrated and fine-tuned with known objects placed at known distances. An experimental proof-of-concept is shown with a human torso phantom, including an aorta phantom and an aneurysm phantom placed in different positions. The results show good imaging capabilities with the potential for detecting and locating possible abdominal aortic aneurysms and reporting acceptable errors.

Fabrication of flexible intracranial aneurysm models using stereolithography 3D printing

Abstract The use of 3D printing technology for medical applications is becoming increasingly popular. Recent stereolithography (SLA)-based printing methods allow the generation of complex structures with a high surface quality. This is particularly useful for applications in the neurovascular field, where sophisticated structures are involved. In this study patient-specific intracranial aneurysm models are extracted based on medical image data und printed as thin-walled vascular phantom models. For this purpose, two commercially available 3D printers are used to print flexible vascular models with three different silicone-like elastic resins (Ultracur3D FL 300, Prusament Flex80 and Formlabs Elastic 50A) of various Shore hardness. Three aneurysm models of different size and complexity are chosen. To evaluate the geometric accuracy of the flexible models, angiographic measurements are performed for an exemplary case and morphological parameters are extracted from the generated 3D models. The printed results demonstrate a successful generation of hollow aneurysm phantoms. There are dependencies regarding the print quality from the model to platform positioning for two materials. The quantitative geometric accuracy analysis shows notable differences between the materials. The extracted morphological parameter values for all materials show a mean decrease compared to the original reference model of aneurysm volume (4.5 %) and maximum diameter (1.0 %) as well as an increase of ostium area (6.0 %) and maximum height (4.9 %). However, Formlabs Elastic 50A in particular exhibits just slight reductions with respect to the reference model, with a mean decrease for all parameters of 5.7 % as well as no dependence on printing position and resulting artifacts. The study investigates the feasibility of using SLA-based 3D printing to generate realistic flexible aneurysm phantoms. In this context, the Formlabs Elastic 50A could be identified as potentially applicable for phantom creation in terms of reproducible quality and geometric validity.

Towards Prediction of Blood Flow in Coiled Aneurysms Before Treatment: A Porous Media Approach.

Modeling blood flow in aneurysms treated with coils could be used to understand the complete embolization of the aneurysm, through thrombus formation that fills the entire sac. Modeling of the endovascular coil mass as a porous medium is a technique that allows for study of aneurysm hemodynamics, efficiently for patient-specific treatment outcome predictions. Models in the literature use mean porosity of coils in the aneurysmal volume, proving inadequate for outcome prediction. However, models that consider heterogeneous porosity distribution have shown more accurate hemodynamics. We recently published the porous crown model, considering the heterogeneous coil mass distribution, validated on two patients. This study aims (i) to validate the porous crown model for a larger cohort (eight patients), and (ii) to propose a porous medium model translatable to clinical practice in treatment planning. We analyzed the porosity distribution of the endovascular coils deployed inside the cerebral aneurysm phantoms of eight patients using 3D x-ray synchrotron images. The permeability and inertial factor of the porous crown model are calculated using previously published methodology. We propose a new "bilinear" porous model, that uses the same hypothesis, but the permeability and inertial factor can be defined from just basic information available in the neuro-suite, i.e., the aneurysmal sac volume and the coil volume fraction targeted by the neurosurgeon. These two models are compared to the coil-resolved simulations, considered as the gold standard. The results show that both the porous crown model and the bilinear model produce similarly accurate hemodynamics in the aneurysm. The error in the standard (mean porosity) porous model is 66%, whereas the error of the bilinear model is 26%, compared to the coil-resolved. The bilinear model is promising as a means of treatment outcome prediction at time of intervention.

Multi-angled simultaneous biplane High-Speed Angiography (HSA) of patient-specific 3D-printed aneurysm phantoms using 1000 fps CdTe Photon-Counting Detectors (PCD's).

1000 fps HSA enables visualization of flow details, which may be important in accurately guiding interventional procedures; however, single-plane imaging may lack clear visualization of vessel geometry and flow detail. The previously presented high-speed orthogonal biplane imaging may overcome these limitations but may still result in foreshortening of vessel morphology. In certain morphologies, acquiring two non-orthogonal biplane projections at multiple angles can provide better flow detail rather than a standard orthogonal biplane acquisition. Flow studies of aneurysm models were performed, where simultaneous biplane acquisitions at various angles separating the two detector views allowed for better evaluation of morphology and flow. 3D-printed, patient-specific internal carotid artery aneurysm models were imaged with various non-orthogonal angles between the two high-speed photon-counting detectors (7.5 cm x 5 cm FOV) to provide frame-correlated simultaneous 1000-fps image sequences. Fluid dynamics were visualized in multi-angled planes of each model using automated injections of iodine contrast media. The resulting dual simultaneous frame-correlated 1000-fps acquisitions from multiple planes of each aneurysm model provided improved visualization of complex aneurysm geometries and flow streamlines. Multi-angled biplane acquisitions with frame correlation allows for further understanding of aneurysm morphology and flow details: additionally, the ability to recover fluid dynamics at depth enables accurate analysis of 3D flow streamlines, and it is expected that multiple-planar views will enable better volumetric flow visualization and quantification. Such better visualization has the potential to improve interventional procedures.

Comparison of pulsatile flow dynamics before and after endovascular intervention in 3D-printed patient-specific internal carotid artery aneurysm models using 1000 fps photon-counting detectors for Simultaneous Biplane High Speed Angiography (SB-HSA).

A significant challenge regarding the treatment of aneurysms is the variability in morphology and analysis of abnormal flow. With conventional DSA, low frame rates limit the flow information available to clinicians at the time of the vascular intervention. With 1000 fps High-Speed Angiography (HSA), high frame rates enable flow details to be better resolved for endovascular interventional guidance. The purpose of this work is to demonstrate how 1000 fps biplane-HSA can be used to differentiate flow features, such as vortex formation and endoleaks, amongst patient-specific internal carotid artery aneurysm phantoms pre- and post-endovascular intervention using an in-vitro flow setup. The aneurysm phantoms were attached to a flow loop configured to a carotid waveform, with automated injections of contrast media. Simultaneous Biplane High-Speed Angiographic (SB- HSA) acquisitions were obtained at 1000 fps using two photon-counting detectors with the respective aneurysm and inflow/ outflow vasculature in the FOV. After x-rays were turned on, the detector acquisitions occurred simultaneously, during which iodine contrast was injected at a continuous rate. A pipeline stent was then deployed to divert flow from the aneurysm, and image sequences were once again acquired using the same parameters. Optical Flow, an algorithm that calculates velocity based on spatial-temporal intensity changes between pixels, was used to derive velocity distributions from HSA image sequences. Both the image sequences and velocity distributions indicate detailed changes in flow features amongst the aneurysms before and after deployment of the interventional device. SB-HSA can provide detailed flow analysis, including streamline and velocity changes, which may be beneficial for interventional guidance.

Modeling Flow in Cerebral Aneurysm After Coils Embolization Treatment: A Realistic Patient-Specific Porous Model Approach.

Computational fluid dynamics (CFD) has been used to evaluate the efficiency of endovascular treatment in coiled cerebral aneurysms. The explicit geometry of the coil mass cannot typically be incorporated into CFD simulations since the coil mass cannot be reconstructed from clinical images due to its small size and beam hardening artifacts. The existing methods use imprecise porous medium representations. We propose a new porous model taking into account the porosity heterogeneity of the coils deployed in the aneurysm. The porosity heterogeneity of the coil mass deployed inside two patients' cerebral aneurysm phantoms is first quantified based on 3D X-ray synchrotron images. These images are also used to compute the permeability and the inertial factor arising in porous models. A new homogeneous porous model (porous crowns model), considering the coil's heterogeneity, is proposed to recreate the flow within the coiled aneurysm. Finally, the validity of the model is assessed through comparisons with coil-resolved simulations. The strong porosity gradient of the coil measured close to the aneurysmal wall is well captured by the porous crowns model. The permeability and the inertial factor values involved in this model are closed to the ideal homogeneous porous model leading to a mean velocity in the aneurysmal sac similar as in the coil-resolved model. The porous crowns model allows for an accurate description of the mean flow within the coiled cerebral aneurysm.

Volumetric surveillance of brain aneurysms: Pitfalls of MRA.

Untreated brain aneurysms are usually surveilled with serial MR imaging and evaluated with 2D multiplanar measurements. The assessment of aneurysm growth may be more accurate with volumetric analysis. We evaluated the accuracy of a magnetic resonance angiography (MRA) segmentation pipeline for aneurysm volume measurement and surveillance. A pipeline to determine aneurysm volume was developed and tested on two aneurysm phantoms imaged with time-of flight (TOF) MRA and 3D rotational angiography (3DRA). The accuracy of the pipeline was then evaluated by reconstructing 10 aneurysms imaged with contrast enhanced-MRA (CE-MRA) and 3DRA. This calibrated and refined post-processing pipeline was subsequently used to analyse aneurysms from our prospectively acquired database. Volume changes above the threshold of error were considered true volume changes. The accuracy of these measurements was analysed. TOF-MRA reconstructions were not as accurate as CE-MRA reconstructions. When compared to 3DRA, CE-MRA underestimated aneurysm volume by 7.8% and did not accurately register the presence of blebs. Eighteen aneurysms (13 saccular and 5 fusiform) were analysed with the optimized 3D volume reconstruction pipeline, with a mean follow-up time of 11 months. Artifact accounted for 10.2% error in volume measurements using serial CE-MRA. When this margin of error was used to assess aneurysms volume in serial imaging with CE-MRA, only two fusiform aneurysms changed in volume. The variations in volume of these two fusiform aneurysms were caused by intra-mural and intrasaccular thrombosis. CE-MRA and TOF-MRA 3D volume reconstructions may not register minor morphological changes such as the appearance of blebs. CE-MRA underestimates volume by 7.8% compared to 3DRA. Serial CE-MRA volume measurements had a larger margin of error of approximately 10.2%. MRA-based volumetric measurements may not be appropriate for aneurysm surveillance.

A patient-specific multi-modality abdominal aortic aneurysm imaging phantom

PurposeMultimodality imaging of the vascular system is a rapidly growing area of innovation and research, which is increasing with awareness of the dangers of ionizing radiation. Phantom models that are applicable across multiple imaging modalities facilitate testing and comparisons in pre-clinical studies of new devices. Additionally, phantom models are of benefit to surgical trainees for gaining experience with new techniques. We propose a temperature-stable, high-fidelity method for creating complex abdominal aortic aneurysm phantoms that are compatible with both radiation-based, and ultrasound-based imaging modalities, using low cost materials.MethodsVolumetric CT data of an abdominal aortic aneurysm were acquired. Regions of interest were segmented to form a model compatible with 3D printing. The novel phantom fabrication method comprised a hybrid approach of using 3D printing of water-soluble materials to create wall-less, patient-derived vascular structures embedded within tailored tissue-mimicking materials to create realistic surrounding tissues. A non-soluble 3-D printed spine was included to provide a radiological landmark.ResultsThe phantom was found to provide realistic appearances with intravascular ultrasound, computed tomography and transcutaneous ultrasound. Furthermore, the utility of this phantom as a training model was demonstrated during a simulated endovascular aneurysm repair procedure with image fusion.ConclusionWith the hybrid fabrication method demonstrated here, complex multimodality imaging patient-derived vascular phantoms can be successfully fabricated. These have potential roles in the benchtop development of emerging imaging technologies, refinement of novel minimally invasive surgical techniques and as clinical training tools.

The Supera Interwoven Nitinol Stent as a Flow Diverting Device in Popliteal Aneurysms

PurposeThe feasibility of using a compressed interwoven Supera stent as a flow diverting device for popliteal aneurysms was recently demonstrated in patients. It is unclear, however, what the optimal flow diverting strategy is, because of the fusiform shape of popliteal aneurysms and their exposure to triphasic flow. To assess this flow diverting strategy for popliteal aneurysms, flow profiles and thrombus formation likelihood were investigated in popliteal aneurysm models.Materials and MethodsSix popliteal aneurysm models were created and integrated into a pulsatile flow set-up. These models covered a bent and a straight anatomy in three configurations: control, single-lined and dual-lined Supera stents. Two-dimensional flow velocities were visualized by laser particle image velocimetry. In addition, the efficacy of the stent configurations for promoting aneurysm thrombosis was assessed by simulations of residence time and platelet activation.ResultsOn average for the two anatomies, the Supera stent led to a twofold reduction of velocities in the aneurysm for single-lined stents, and a fourfold reduction for dual-lined stents. Forward flow was optimally diverted, whereas backward flow was generally deflected into the aneurysm. The dual-lined configuration led to residence times of 15–20 s, compared to 5–15 s for the single stent configurations. Platelet activation potential was not increased by the flow diverting stents.ConclusionA compressed Supera stent was successfully able to divert flow in a popliteal aneurysm phantom. A dual-lined configuration demonstrated superior hemodynamic characteristics compared to its single-lined counterpart.

Navigation of a magnetic micro-robot through a cerebral aneurysm phantom with magnetic particle imaging

Cerebral aneurysms are potentially life threatening and nowadays treated by a catheter-guided coiling or by a neurosurgical clipping intervention. Here, we propose a helically shaped magnetic micro-robot, which can be steered by magnetic fields in an untethered manner and could be applied for a novel coiling procedure. This is shown by navigating the micro-robot through an additively manufactured phantom of a human cerebral aneurysm. The magnetic fields are applied with a magnetic particle imaging (MPI) scanner, which allows for the navigation and tomographic visualization by the same machine. With MPI the actuation process can be visualized with a localization accuracy of 0.68 mm and an angiogram can be acquired both without any radiation exposure. First in-vitro phantom experiments are presented, showing an idea of a robot conducted treatment of cerebral aneurysms.

Utility of 3D printed abdominal aortic aneurysm phantoms: a systematic review.

3D printed (3DP) abdominal aortic aneurysm (AAA) phantoms are emerging in the literature as an adjunct for the visualization of complex anatomy, particularly for presurgical device selection and simulation. This is the first systematic review to provide a comprehensive overview of 3DP for endovascular aneurysm repair (EVAR) planning and intervention, evaluating the readiness of current levels of technology for mainstream implementation. A systematic literature search of PubMed and MEDLINE was performed as per PRISMA guidelines using the terms '3D Printing', 'AAA' OR 'EVAR' and related index terms, and further relevant articles were appraised via a snowballing approach. Our last search was conducted on 14 November 2020. Twenty-five articles were identified for critical analysis, with 14 cases or technical reports. Nineteen publications utilized 3DP AAA phantoms to aid presurgical decision making, device selection and design. Four publications explored the utility of 3DP phantoms as EVAR trainers, and one publication examined the technology as a tool for patient education. Flexible, transparent phantoms were deemed most useful; however, the cost and availability of higher end machines limited accessibility. 3DP phantoms have been used in EVAR to facilitate visualization of complex patient anatomy, appropriate device selection, in predicting navigational difficulties and the shape and position of endograft after deployment. These phantoms show promise in reducing known complications such as endoleak, stent graft occlusion and migration; however, larger scale prospective studies are required to validate its impacts on patient outcomes and cost savings to the healthcare system.

Design, Development, and Temporal Evaluation of a Magnetic Resonance Imaging-Compatible In Vitro Circulation Model Using a Compliant Abdominal Aortic Aneurysm Phantom.

Biomechanical characterization of abdominal aortic aneurysms (AAAs) has become commonplace in rupture risk assessment studies. However, its translation to the clinic has been greatly limited due to the complexity associated with its tools and their implementation. The unattainability of patient-specific tissue properties leads to the use of generalized population-averaged material models in finite element analyses, which adds a degree of uncertainty to the wall mechanics quantification. In addition, computational fluid dynamics modeling of AAA typically lacks the patient-specific inflow and outflow boundary conditions that should be obtained by nonstandard of care clinical imaging. An alternative approach for analyzing AAA flow and sac volume changes is to conduct in vitro experiments in a controlled laboratory environment. In this study, we designed, built, and characterized quantitatively a benchtop flow loop using a deformable AAA silicone phantom representative of a patient-specific geometry. The impedance modules, which are essential components of the flow loop, were fine-tuned to ensure typical intraluminal pressure conditions within the AAA sac. The phantom was imaged with a magnetic resonance imaging (MRI) scanner to acquire time-resolved images of the moving wall and the velocity field inside the sac. Temporal AAA sac volume changes lead to a corresponding variation in compliance throughout the cardiac cycle. The primary outcome of this work was the design optimization of the impedance elements, the quantitative characterization of the resistive and capacitive attributes of a compliant AAA phantom, and the exemplary use of MRI for flow visualization and quantification of the deformed AAA geometry.

Low-Dose 3D Rotational Angiography in Measuring the Size of Intracranial Aneurysm: In Vitro Feasibility Study Using Aneurysm Phantom

PurposeThree-dimensional (3D) measurement of intracranial aneurysms is important in planning endovascular treatment, and 3D rotational angiography (RA) is effective in accurate measurement. The purpose of this study was to evaluate the feasibility of low dose 3D RA (5 seconds 0.10 μGy/frame) in measuring an intracranial aneurysm using an in vitro phantom.Materials and MethodsWe investigated an in vitro 3D phantom of an intracranial aneurysm with 10 acquisitions of 3D RA with a conventional dose (5 seconds 0.36 μGy/frame) and 10 acquisitions with a low-dose (5 seconds 0.10 μGy/frame). 3D size and neck diameters of the aneurysm were measured and compared between the 2 groups (conventional and low-dose) using noninferiority statistics.ResultsThe aneurysm measurements were well-correlated between the 2 readers, and noninferiority in the measurement of aneurysmal size of low-dose 3D RA was demonstrated, as the upper margin of the 1-sided 97.5% confidence interval did not cross the pre-defined noninferiority margin of 0.2 mm by the 2 readers.ConclusionLow-dose (5 seconds 0.10 μGy/frame) cerebral 3D RA is technically feasible and not inferior in in vitro 3D measurement of an intracranial aneurysm. Thus, low-dose 3D RA is promising and needs further evaluation for its clinical utility in the planning of endovascular treatment of an intracranial aneurysm.

Postinterventional Assessment after Stent and Flow-Diverter Implantation Using CT: Influence of Spectral Image Reconstructions and Different Device Types.

CTA provides a noninvasive alternative technique to DSA in the follow-up after endovascular aneurysm treatment to evaluate aneurysm occlusion and exclude intraluminal narrowing after stent or flow-diverter implantation; however, assessability may be impeded by stent material artifacts. The objective of this in vitro study was to compare the visual assessability of different conventional stents and flow diverters as well as different reconstructions of dual-layer CT images. Four conventional intracranial stents and 4 flow diverters were implanted in identical aneurysm phantoms. Conventional and monoenergetic images (40, 50, 60, 90, 120, 180 keV) were acquired to evaluate attenuation alteration, visible lumen diameter, and SNR. Image quality was rated subjectively by 2 independent radiologists using a 4-point Likert scale. Low kiloelectron volt (40-60 keV) monoenergetic reconstructions showed an improved SNR and an improved lumen density ratio compared with high kiloelectron volt reconstructions (90-180 keV) and conventional reconstructions, however without reaching significance compared with the latter. Assessment of the adjacent aneurysm and subjective evaluation was not affected by the imaging technique and stent type. Artifact susceptibility varied with the device used and increased among flow diverters. Low kiloelectron volt reconstructions improved the assessment of the stent lumen in comparison with high kiloelectron volt reconstructions. No significant improvement in image quality could be shown compared with conventional images. For some devices, iodine-specific reconstructions led to severe artifacts and are therefore not recommended. There was no relevant improvement in the assessability of the adjacent aneurysm.

Accuracy and reliability of computer-assisted semi-automated morphological analysis of intracranial aneurysms: an experimental study with digital phantoms and clinical aneurysm cases.

Morphological parameters are very important for predicting aneurysm rupture. However, due to geometric radiographic distortion and plane/angle selection bias, the traditional manual measurements (MM) of aneurysm morphology are inaccurate and suffer from severe variability. Our study is to evaluate the accuracy and reliability of computer-assisted semi-automated measurement (CASAM) of intracranial aneurysms, which is a novel technique in aneurysm measurement. An in-house software for CASAM was developed. Classical morphology indices including aneurysm diameter, neck size, height, width, volume, inflow angle, and aspect ratio were measured. To validate the accuracy and robustness of the semi-automated measurements, 20 digital intracranial aneurysm phantoms and 27 clinical aneurysms with different locations and sizes were measured using MM or CASAM. In the phantom study, although the inter-observer variability of both the MM and CASAM was very low, the manual measurements had higher errors (1.7-19.1%), while the CASAM yielded more accurate results (errors of 1.1-2.5%). The consistency test indicated that the CASAM results were highly consistent with the actual values (concordance correlation coefficient = 0.993). In the clinical study, CASAM showed better intraclass correlation coefficient values compared with MM. The inflow angle had low consistency in both groups. We successfully developed a computer-assisted method to semi-automatically measure the morphological parameters of aneurysm. According to our study, CASAM of aneurysm morphological parameters is a more precise and reliable way than MM to obtain accurate aneurysm morphological parameters. This method is worthy of further studies to promote its clinical use.

Evaluation of Two Fast Virtual Stenting Algorithms for Intracranial Aneurysm Flow Diversion

Endovascular treatment of intracranial aneurysms (IAs) by flow diverter (FD) stents depends on flow modification. Patient-specific modeling of FD deployment and computational fluid dynamics (CFD) could enable a priori endovascular strategy optimization. We developed a fast, simplistic, expansion-free balls-weeping algorithm to model FDs in patientspecific aneurysm geometry. However, since such strong simplification could result in less accurate simulations, we also developed a fast virtual stenting workflow (VSW) that explicitly models stent expansion using pseudo-physical forces. To test which of these two fast algorithms more accurately simulates real FDs, we applied them to virtually treat three representative patient-specific IAs. We deployed Pipeline Embolization Device into 3 patient-specific silicone aneurysm phantoms and simulated the treatments using both balls-weeping and VSW algorithms in computational aneurysm models. We then compared the virtually deployed FD stents against experimental results in terms of geometry and post-treatment flow fields. For stent geometry, we evaluated gross configurations and porosity. For post-treatment aneurysmal flow, we compared CFD results against experimental measurements by particle image velocimetry. We found that VSW created more realistic FD deployments than balls-weeping in terms of stent geometry, porosity and pore density. In particular, balls-weeping produced unrealistic FD bulging at the aneurysm neck, and this artifact drastically increased with neck size. Both FD deployment methods resulted in similar flow patterns, but the VSW had less error in flow velocity and inflow rate. In conclusion, modeling stent expansion is critical for preventing unrealistic bulging effects and thus should be considered in virtual FD deployment algorithms. Also endowed with its high computational efficiency and superior accuracy, the VSW algorithm is a better candidate for implementation into a bedside clinical tool for FD deployment simulation.