Patient-specific Aneurysm Models Research Articles

Development of a bioresorbable self-expanding microstent for interventional applications – an innovative approach for stent-assisted coiling

Objectives Stent-assisted coiling prevents coil migration in broad-based intracranial aneurysms. So far, only permanent metal stents are approved for intracranial use. Bioresorbable stents allow a new therapeutic approach that may prevent the need for lifelong anticoagulation. We developed a neurovascular bioresorbable microstent (NBRS) and compared it in vitro to the commercial Neuroform EZ stent. Materials and Methods The self-expanding NBRS design is oriented on the Neuroform EZ stent. Poly L-lactic acid (PLLA) was used to manufacture semi-finished products in a dipping process. For the compensation of the inferior material properties of PLLA, design adjustments were made. The NBRS were cut by means of femtosecond (fs) laser and were morphologically and mechanically compared in vitro to the Neuroform EZ stent. In vitro implantation of an NBRS was performed using a complex patient-specific 3D-printed aneurysm model. In addition, an in vitro coiling procedure to assess the stent’s ability to support a coil package was conducted. Results The NBRS could be reproducibly manufactured and had high quality regarding surface morphology. The radial force at the indicated vessel diameter of 3.0 mm was slightly higher for the Neuroform EZ stent compared to the NBRS. The self-expansion ability of the NBRS could be proven. The kink behavior of the NBRS was comparable to that of the Neuroform EZ stent, so no vessel lumen size reduction is expected. The stents showed identical deformation under local compression of 25 % based on the initial diameter, resulting in maximum forces of 24 ± 5 mN (Neuroform EZ) and 8 ± 2 mN (NBRS). The implanted NBRS expanded uniformly, and proper vessel wall adaptation was observed. The NBRS has the ability to retain a coil package. Conclusion This study reported a reproducible manufacturing process for the developed NBRS as well as mechanical and morphological in vitro tests. Furthermore, successful NBRS implantation into a complex patient-specific vessel model was presented as proof of concept. The promising results of this study, also considering the commercial Neuroform EZ stent, support the idea of fully biodegradable microstents for intracranial aneurysm treatment. Key Points

Aneurysm Rupture Prediction Based on Strain Energy-CFD Modelling.

This paper presents a Patient-Specific Aneurysm Model (PSAM) analyzed using Computational Fluid Dynamics (CFD). The PSAM combines the energy strain function and stress-strain relationship of the dilated vessel wall to predict the rupture of aneurysms. This predictive model is developed by analyzing ultrasound images acquired with a 6-9 MHz Doppler transducer, which provides real-time data on the arterial deformations. The patient-specific cyclic loading on the PSAM is extrapolated from the strain energy function developed using historical stress-strain relationships. Multivariant factors are proposed to locate points of arterial weakening that precede rupture. Biaxial tensile tests are used to calculate the material properties of the artery wall, enabling the observation of the time-dependent material response in wall rupture formation. In this way, correlations between the wall deformation and tissue failure mode can predict the aneurysm's propensity to rupture. This method can be embedded within the ultrasound measures used to diagnose potential AAA ruptures.

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.

2D versus 3D comparison of angiographic imaging biomarkers using computational fluid dynamics simulations of contrast injections.

Quantitative angiography (QAngio) may provide hemodynamic information during neurointerventional procedures through imaging biomarkers related to contrast flow. The standard clinical implementation of QAngio is limited by projection imaging: analysis of contrast motion within complex 3D geometries is restricted to 1-2 projection views, truncating the potential wealth of imaging biomarkers related to disease progression or efficacy of treatment. To understand the limitations of 2D biomarkers, we propose the use of in-silico contrast distributions to investigate the potential benefits of 3D-QAngio within the context of neurovascular hemodynamics. Ground-truth in-silico contrast distributions were generated in two patient-specific intracranial aneurysm models, accounting for the physical interactions of contrast media and blood. A short bolus of contrast was utilized to obtain full a wash-in/ wash-out cycle within the aneurysm ROI. Simulated angiograms mimicking clinical cone-beam CT (CBCT) acquisitions were then generated, and volumetric contrast distributions were reconstructed to analyze bulk contrast flow. The ground-truth 3D-CFD, reconstructed 3D-CBCT-DSA, and 2D-DSA projections were used to extract QAngio parameters related to contrast time dilution curves, such as area under the curve (AUC), peak height (PH), mean-transit-time (MTT), time-to-peak (TTP), and time to arrival (TTA). An initial comparison of quantitative flow parameters in both 2D and 3D, in a smaller and larger aneurysm, indicated that 3D-QAngio can provide a good description of bulk flow characteristics (TTA, TTP, MTT), but recovery of integral parameters (PH, AUC) aneurysms is limited. Nonetheless, incorporation of 3D-QAngio methods may provide additional insight into our understanding of abnormal vascular flow patterns.

Influence of blood viscosity models and boundary conditions on the computation of hemodynamic parameters in cerebral aneurysms using computational fluid dynamics.

Computational fluid dynamics (CFD) is widely used to calculate hemodynamic parameters that are known to influence cerebral aneurysms. However, the boundary conditions for CFD are chosen without any specific criteria. Our objective is to establish the recommendations for setting the analysis conditions for CFD analysis of the cerebral aneurysm. The plug and the Womersley flow were the inlet boundary conditions, and zero and pulsatile pressures were the outlet boundary conditions. In addition, the difference in the assumption of viscosity was analyzed with respect to the flow rate. The CFD process used in our research was validated using particle image velocimetry experiment data from Tupin et al.'s work to ensure the accuracy of the simulations. It was confirmed that if the entrance length was sufficiently secured, the inlet and outlet boundary conditions did not affect the CFD results. In addition, it was observed that the difference in the hemodynamic parameter between Newtonian and non-Newtonian fluid decreased as the flow rate increased. Furthermore, it was confirmed that similar tendencies were evaluated when these recommendations were utilized in the patient-specific cerebral aneurysm models. These results may help conduct standardized CFD analyses regardless of the research group.

Effect of wall elasticity on flow instability and wall shear stress vof a patient-specific aneurysm model in middle cerebral artery

Effect of wall elasticity on flow instability and wall shear stress vof a patient-specific aneurysm model in middle cerebral artery

Developing an in vitro validated 3D in silico internal carotid artery sidewall aneurysm model.

Introduction: Direct quantification of hemodynamic factors applied to a cerebral aneurysm (CA) remains inaccessible due to the lack of technologies to measure the flow field within an aneurysm precisely. This study aimed to develop an in vitro validated 3D in silico patient-specific internal carotid artery sidewall aneurysm (ICASA) model which can be used to investigate hemodynamic factors on the CA pathophysiology. Methods: The validated ICASA model was developed by quantifying and comparing the flow field using particle image velocimetry (PIV) measurements and computational fluid dynamics (CFD) simulations. Specifically, the flow field characteristics, i.e., blood flowrates, normalized velocity profiles, flow streamlines, and vortex locations, have been compared at representative time instants in a cardiac pulsatile period in two designated regions of the ICASA model, respectively. One region is in the internal carotid artery (ICA) inlet close to the aneurysm sac, the other is across the middle of the aneurysmal sac. Results and Discussion: The results indicated that the developed computational fluid dynamics model presents good agreements with the results from the parallel particle image velocimetry and flowrate measurements, with relative differences smaller than 0.33% in volumetric flow rate in the ICA and relative errors smaller than 9.52% in averaged velocities in the complex aneurysmal sac. However, small differences between CFD and PIV in the near wall regions were observed due to the factors of slight differences in the 3D printed model, light reflection and refraction near arterial walls, and flow waveform uncertainties. The validated model not only can be further employed to investigate hemodynamic factors on the cerebral aneurysm pathophysiology statistically, but also provides a typical model and guidance for other professionals to evaluate the hemodynamic effects on cerebral aneurysms.

Immediate flow-diversion characteristics of a novel primarily bioresorbable flow-diverting stent.

Flow-diverting stents with a resorbable component have significant theoretical benefits over full metal stents, although currently there are none in clinical use. In this study, the authors sought to determine the immediate flow-diversion characteristics of a novel primarily bioresorbable flow-diverting stent. Bioresorbable stents were deployed into glass tube models to determine porosity and pore density. In vitro flow diversion behavior was evaluated using high frame rate angiography under pulsatile flow conditions in a patient-specific silicone aneurysm model treated with the resorbable stent as well as the Surpass Evolve stent. In vivo flow diversion was characterized by deployment into 20 rabbit saccular aneurysm models, and grading was based on the O'Kelly-Marotta scale and the 4F-flow diversion predictive score. Porosities and pore densities of the bioresorbable stent were in the flow-diverting range for all target vessel diameters. Quantified results of immediate angiography after placement of the bioresorbable stent into a silicone aneurysm model demonstrated greater flow diversion compared to the Evolve stent. Bioresorbable stent placement in saccular aneurysm models resulted in an immediate O'Kelly-Marotta grade of A3 or better and a 4F-flow diversion predictive score of 4 or better in all cases. The bioresorbable stent has immediate flow-diversion characteristics that are comparable to commercially available metal stents. Longer-term studies are underway to determine the ability of the resorbable fibers to act as a neointimal scaffold and result in long-term aneurysm occlusion.

Characteristic effect of wall elasticity on flow instability and wall shear stress of a full-scale, patient-specific aneurysm model in the middle cerebral artery: An experimental approach

The mechanisms underlying the growth and rupture of aneurysms are poorly understood. Although the wall shear stress (WSS) in elastic aneurysm models is examined using fluid-structure interaction (FSI) simulations, it has not been sufficiently validated using experimental modalities, such as particle image velocimetry (PIV) or phase contrast magnetic resonance imaging (PC-MRI). In this study, we investigated pulsatile flow in an elastic, image-based, patient-specific cerebral aneurysm model using PIV. The phantom model was carefully fabricated using a specialized technique by silicone elastomer. We explored the hemodynamics of the WSS and the kinetic energy cascade (KEC) in the elastic model compared with a rigid model, at the apex of the bifurcation of the middle cerebral artery (MCA) in vitro. The effects of elasticity on the WSS, WSS gradient (WSSG), and tensile strength of the aneurysm wall were also investigated, in addition to the effect of wall elasticity on the KEC compared to a rigid wall. Although the WSSG around the stagnation point had a large positive value, there was no difference between the two models. In particular, wall elasticity suppressed the WSS magnitude around the stagnation point and attenuated the KEC (i.e., the flow fluctuation). Future studies examining KEC frequency and WSS characteristics in a phantom model should consider assessing elasticity.

Modeling Flow Diverters Using a Porous Medium Approach: A Fast Alternative to Virtual Flow Diverter Deployment

The Tubridge flow diverter (FD) (MicroPort Medical Co. Ltd., Shanghai, China) is a novel device aimed at reconstructing the parent artery and eliminating the aneurysm. Numerical simulations based on virtual FD deployment allow the assessment of the complex nature of aneurismal flow changes before the actual intervention but are demanding on computational resources. Here, we evaluate an alternative strategy of modeling FD effects for the Tubridge system using a porous medium. The goal of this study is to reduce demands on time and complexity of the simulation procedure for applications in clinical research. Ten patient-specific aneurysm models were reconstructed from retrospectively collected diagnostic 3-dimensional digital subtraction angiographic images. Virtual FDs were deployed (SolidWorks, Dassault Systems, Concord, Massachusetts, USA; Meshmixer, Autodesk, San Rafael, California, USA) and corresponding porous medium patches were constructed at the ostium with a research computational fluid dynamics prototype (Siemens Healthineers, Forchheim, Germany). Hemodynamic conditions were simulated in 2 approaches. Hemodynamics inside the aneurysm based on these 2 approaches were compared. Both approaches yielded similar results. Mean wall shear stress and mean pressure of the aneurysmal wall correlated significantly (r= 0.8, r= 1.0, P < 0.05) as did mean velocity and mean pressure at a region inside the aneurysm, at the ostium and at a cross section containing the main vertex (for velocities r= 0.9; for pressures r= 1.0, P < 0.05). The use of porous medium patches reduced the preparation and simulation time together by approximately 50%. Using a porous medium approach yields comparable mean values for hemodynamic alterations compared to direct virtual FD simulations. Additionally, the porous medium approach greatly reduced the modeling complexity and computation time.

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

BackgroundPipeline 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...

Rehearsals using patient-specific 3D-printed aneurysm models for simulation of endovascular embolization of complex intracranial aneurysms: 3D SIM study

BackgroundIn neurovascular treatment planning, endovascular devices to manage complex intracranial aneurysms requiring intervention are often selected based on conventional measurements and interventional neuroradiologist experience. A recently developed technology allows a patient-specific 3D-printed model to mimic the navigation experience. The goal of this study was to assess the effect of pre-procedure 3D simulation on procedural and clinical outcomes for wide-neck aneurysm embolization. Materials & methodsIn this unblinded, non-randomized, prospective, multicenter study conducted from November 18 through December 20, patients with complex intracranial aneurysms (neck > 4 mm or ratio < 21) were treated by WEB or flow diverter stents (FDS). The primary endpoint was concordance between simulation and procedure, 3D-printed model accuracy as well as embolization outcomes including complications, procedure times, and radiation dose were also assessed. Secondary endpoint was to compare versus a retrospective WEB cohort. ResultsTwenty-one patients were treated, 76% of cases by WEB and 24% by FDS. Concordance between post-simulation and real procedure efficiency was 0.85 [0.69 – 1.00] for size device selection and 0.93 [0.79 – 1.00] for wall-apposition/aneurysm neck closure. Geometrical accuracy of the 3D-printed model showed a mean absolute shift of 0.11 mm. Two complications without major clinical impact were reported with a post-operative mRS similar to pre-procedure mRS for all patients. ConclusionsRehearsal using accurate 3D-printed patient-specific aneurysm models enabled optimization of embolization strategy, resulting in reduced procedure duration and cumulative fluoroscopy time which translated to reduced radiation exposure compared to procedures performed without simulation.

Patient-Specific Biomechanics in Marfan Ascending Thoracic Aortic Aneurysms

BackgroundGuidelines for sinus of Valsalva (SOV)-thoracic aortic aneurysms in Marfan syndrome recommend size-based criteria for elective surgical repair. Biomechanics may provide a better prediction of dissection risk than diameter. Our aim was to determine magnitudes of wall stress in the aortic root of Marfan patients using finite element analyses. MethodsForty-six Marfan patients underwent patient-specific 3-dimensional SOV-thoracic aortic aneurysm geometry reconstruction using imaging data. Finite element analyses were performed to determine wall stress distributions at SOV, sinotubular junction (STJ), and ascending aorta (AscAo) at systole. ResultsPeak circumferential stresses were 432.8 ± 111 kPa, 408.1 ± 88.3 kPa, and 321.9 ± 83.8 kPa at the SOV, STJ, and AscAo, respectively, with significant differences between SOV and AscAo (P < 3.08E-07), and STJ and AscAo (P < 2.26E-06). Peak longitudinal wall stresses were 352 ± 73.9 kPa, 277.5 ± 89.5 kPa, and 200.6 ± 81 kPa at SOV, STJ, and AscAo, respectively, with significant differences between SOV and STJ (P < 6.01E-06), SOV and AscAo (P < 9.79E-13), and STJ and AscAo (P < 3.34E-07). Diameter was not correlated to wall stresses. Comparison of wall stresses in aneurysm <5 cm vs ≥5 cm and <4.5 cm vs ≥4.5 cm showed no significant differences in wall stresses in the circumferential or longitudinal direction. ConclusionsPeak wall stresses in Marfan SOV- thoracic aortic aneurysm were greatest in SOV than STJ than AscAo. Diameter was poorly correlated to peak stresses such that current guidelines with 5 cm cutoff had significant overlap in peak stresses in patients with <5 cm vs ≥5 cm. Use of patient-specific Marfan aneurysm models may identify patients with high wall stresses and small aneurysms who could benefit from earlier surgical repair to prevent aortic dissection.

Integrating multi-fidelity blood flow data with reduced-order data assimilation

High-fidelity patient-specific modeling of cardiovascular flows and hemodynamics is challenging. Direct blood flow measurement inside the body with in-vivo measurement modalities such as 4D flow magnetic resonance imaging (4D flow MRI) suffer from low resolution and acquisition noise. In-vitro experimental modeling and patient-specific computational fluid dynamics (CFD) models are subject to uncertainty in patient-specific boundary conditions and model parameters. Furthermore, collecting blood flow data in the near-wall region (e.g., wall shear stress) with experimental measurement modalities poses additional challenges. In this study, a computationally efficient data assimilation method called reduced-order modeling Kalman filter (ROM-KF) was proposed, which combined a sequential Kalman filter with reduced-order modeling using a linear model provided by dynamic mode decomposition (DMD). The goal of ROM-KF was to overcome low resolution and noise in experimental and uncertainty in CFD modeling of cardiovascular flows. The accuracy of the method was assessed with 1D Womersley flow, 2D idealized aneurysm, and 3D patient-specific cerebral aneurysm models. Synthetic experimental data were used to enable direct quantification of errors using benchmark datasets. The accuracy of ROM-KF in reconstructing near-wall hemodynamics was assessed by applying the method to problems where near-wall blood flow data were missing in the experimental dataset. The ROM-KF method provided blood flow data that were more accurate than the computational and synthetic experimental datasets and improved near-wall hemodynamics quantification.

A Brush-Spin-Coating Method for Fabricating In Vitro Patient-Specific Vascular Models by Coupling 3D-Printing.

In vitro patient-specific flexible vascular models are helpful for understanding the haemodynamic changes before and after endovascular treatment and for effective training of neuroendovascular interventionalists. However, it is difficult to fabricate models of overall unified or controllable thickness using existing manufacturing methods. In this study, we developed an improved and easily implemented method by combining 3D printing and brush-spin-coating processes to produce a transparent silicone model of uniform or varied thickness. First, a water-soluble inner-skeleton model, based on clinical data, was printed on a 3D printer. The skeleton model was subsequently fixed in a single-axis-rotation machine to enable continuous coating of silicone, the thickness of which was manually controlled by adsorption and removal of excess silicone in a brush-spinning operation. After the silicone layer was solidified, the inner skeleton was further dissolved in a hot water bath, affording a transparent vascular model with real geometry. To verify the controllability of the coating thickness by using this method, a straight tube, an idealised aneurysm model, a patient-specific aortic arch model, and an abdominal aortic aneurysm model were manufactured. The different thicknesses of the manufactured tubes could be well controlled, with the relative standard deviations being 5.6 and 8.1% for the straight and aneurysm tubes, respectively. Despite of the diameter changing from 33 to 20 mm in the patient-specific aorta, the thickness of the fabricated aortic model remains almost the same along the longitudinal direction with a lower standard deviation of 3.1%. In the more complex patient-specific abdominal aneurysm model, varied thicknesses were realized to mimic the measured data from the CT images, where the middle of the aneurysm was with 2 mm and abdominal aorta as well as the iliac arteries had the normal thickness of 2.3 mm. Through the brush-spin-coating method, models of different sizes and complexity with prescribed thickness can be manufactured, which will be helpful for developing surgical treatment strategies or training neuroendovascular interventionalists.

Study of Extracted Geometry Effect on Patient-Specific Cerebral Aneurysm Model with Different Threshold Coefficient (Cthres)

The recent diagnostic assessment of cerebrovascular disease makes use of computational fluid dynamics (CFD) to quantify blood flow and determine the hemodynamics factors contributing to the disease from patient-specific models. However, compliant and anatomical patient-specific geometries are generally reconstructed from the medical images with different threshold values subjectively. Therefore, this paper tends to present the effect of extracted geometry with different threshold coefficient, Cthres by using a patient-specific cerebral aneurysm model. A set of medical images, digital subtraction angiography (DSA) images from the real patient diagnosed with internal carotid artery (ICA) aneurysm was obtained. The threshold value used to extract the patient-specific cerebral aneurysm geometry was calculated by using a simple threshold determination method. Several threshold coefficients, Cthres such as 0.2, 0.3, 0.4, 0.5 and 0.6 were employed in the image segmentation creating three-dimensional (3D) realistic arterial geometries that were then used for CFD simulation. As a result, we obtained that the volume of patient-specific cerebral aneurysm geometry decreases as the threshold coefficient, Cthres increases. There is dislocation of artery attached to the ICA aneurysm geometry occurred at a high threshold coefficient, Cthres. Besides, the physical changes also bring remarkable physiological effect on the wall shear stress (WSS) distribution and velocity flow field at patient-specific cerebral aneurysm geometry reconstructed with different threshold coefficient, Cthres.

Hemodynamic differences by increasing low profile visualized intraluminal support (LVIS) stent local compaction across intracranial aneurysm orifice.

The Low-profile Visualized Intraluminal Support device (LVIS) has been successfully used to treat cerebral aneurysm, and the push-pull technique has been used clinically to compact the stent across aneurysm orifice. Our aim was to exhibit the hemodynamic effect of the compacted LVIS stent. Two patient-specific aneurysm models were constructed from three-dimensional angiographic images. The uniform LVIS stent, compacted LVIS and Pipeline Embolization Device (PED) with or without coil embolization were virtually deployed into aneurysm models to perform hemodynamic analysis. Intra-aneurysmal flow parameters were calculated to assess hemodynamic differences among different models. The compacted LVIS had the highest metal coverage across the aneurysm orifice (case 1, 46.37%; case 2, 67.01%). However, the PED achieved the highest pore density (case 1, 19.56 pores/mm2; case 2, 18.07 pores/mm2). The compacted LVIS produced a much higher intra-aneurysmal flow reduction than the uniform LVIS. The PED showed a higher intra-aneurysmal flow reduction than the compacted LVIS in case 1, but the results were comparable in case 2. After stent placement, the intra-aneurysmal flow was further reduced as subsequent coil embolization. The compacted LVIS stent with coils produced a similar reduction in intra-aneurysmal flow to that of the PED. The combined characteristics of stent metal coverage and pore density should be considered when assessing the flow diversion effects of stents. More intra-aneurysmal flow reductions could be introduced by compacted LVIS stent than the uniform one. Compared with PED, compacted LVIS stent may exhibit a flow-diverting effect comparable to that of the PED.

Biomodex patient-specific brain aneurysm models: the value of simulation for first in-human experiences using new devices and robotics

BackgroundWith the recent advent of advanced technologies in the field, treatment of neurovascular diseases using endovascular techniques is rapidly evolving. Here we describe our experience with pre-surgical simulation using the...

Haemodynamics in a patient-specific intracranial aneurysm according to experimental and numerical approaches: A comparison of PIV, CFD and PC-MRI

The haemodynamics determined by different approaches for studying fluid dynamics - i.e. computational fluid dynamics (CFD), particle image velocimetry (PIV), and phase-contrast magnetic resonance imaging (PC-MRI) - have rarely been thoroughly compared; nor have the factors that affect accuracy and precision in each method. As each method has its own advantages and limitations, this knowledge is important for future studies to be able to achieve valid analyses of fluid flows. To gauge the capacity of these methods for analysing aneurysmal flows, we compared the haemodynamic behaviours determined by each method within a patient-specific aneurysm model. An in vitro silicone aneurysm model was fabricated for PIV and PC-MRI, and an in silico aneurysm model with the same geometry was reconstructed for CFD. With the same fluid model prepared numerically and physically, CFD, PIV and PC-MRI were performed to study aneurysmal haemodynamics. 2D velocity vectors and magnitudes show good agreement between PIV and CFD, and 3D flow patterns show good similarity between PC-MRI and CFD. These findings give confidence to future haemodynamic studies using CFD technology. For the first time, the morphological inconsistency between the PCMRI model and others is found to affect the measurement of local flow patterns.

In Vitro Assessment of Flow Variability in an Intracranial Aneurysm Model Using 4D Flow MRI and Tomographic PIV.

Aneurysm rupture has been suggested to be related to aneurysm geometry, morphology, and complex flow activity; therefore, understanding aneurysm-specific hemodynamics is crucial. 4D Flow MRI has beenshown to be a feasible tool for assessing hemodynamics in intracranial aneurysms with high spatial resolution. However, it requires averaging over multiple heartbeats and cannot account for cycle-to-cycle hemodynamics variations. This study aimed to assess cycle-to-cycle flow dynamics variations in a patient-specific intracranial aneurysm model using tomographic particle image velocimetry (tomo-PIV) at a high image rate under pulsatile flow conditions. Time-resolved and time-averaged velocity flow fields within the aneurysm sac and estimations of wall shear stress (WSS) were compared with those from 4D Flow MRI. A one-way ANOVA showed a significant difference between cardiac cycles (p value < 0.0001); however, differences were not significant after PIV temporal and spatial resolution was matched to that of MRI (p value 0.9727). This comparison showed the spatial resolution to be the main contributor to assess cycle-to-cycle variability. Furthermore, the comparison with 4D Flow MRI between velocity components, streamlines, and estimated WSS showed good qualitative and quantitative agreement. This study showed the feasibility of patient-specific in-vitro experiments using tomo-PIV to assess 4D Flow MRI with high repeatability in the measurements.