An investigation of abdominal aortic aneurysms (AAAs) is performed based on medical Computed Tomography (CT) images. The images are transformed into 3D surface models to simulate deformation behavior of AAAs and estimate the rupture risk. The finite element method (FEM) with nonlinear hyperelastic Yeoh material model and the linear model for comparison are used. The aorta has been modelled with the shell theory, with appropriate adjustments to take into account the intraluminal thrombus. Numerical results are obtained for the maximum value of the von Mises stresses and strains. The introduced techniques can provide sufficient estimates for the displacements at inaccessible points, like virtual sensors, which can be used for rupture prediction within an integrated artificial intelligence tool.

Abdominal aortic aneurysm refers to the irreversible abnormal dilation of the aorta at the abdominal level, and it is acknowledged as one of the leading causes of mortality on a global scale. Most abdominal aortic aneurysms are asymptomatic until they approach the point of rupture; thus, it is essential to establish an efficient workflow for the accurate detection of this condition to enhance clinical outcomes. The incorporation of artificial intelligence learning algorithms into healthcare workflows holds the prospect of significantly improving the accuracy of decision-making related to patient mortality risk. Since the potential surgical repair of an aortic aneurysm depends upon the maximum external diameter of the aneurysm, this study aims to develop an end-to-end algorithmic method for classifying low-risk and high-risk cases based on abdominal aortic aneurysm data. To perform the predictive analysis, we adopt neuro-fuzzy systems, ensembles of neuro-fuzzy systems, and hybrid evolutionary-based fuzzy classifiers. The models are trained using features extracted from the radiomics framework and exhibit high generalisation performance, as measured by the adopted metrics, and estimated on a K-fold cross-validation basis. Numerical studies further reveal that the hybrid evolutionary-based fuzzy system exhibits exceptional accuracy in distinguishing between the two identified classes.

Background/Objectives: This study compared the hemodynamic performance of fenestrated (FEVAR), branched (BEVAR), and chimney endovascular aortic aneurysm repair (chEVAR) in patients with complex aortic aneurysms. Methods: The pre- (native) and post-endovascular repair (endograft-defined) blood lumen was reconstructed from computed tomography angiographies of nine (9) elective patients treated with FEVAR (n = 3), BEVAR (n = 3), and chEVAR (n = 3). Computational fluid dynamics (CFD) simulations obtained blood flow properties. Velocity magnitude, wall shear stress (WSS), time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), relative residence time (RRT), and local normalized helicity (LNH) were computed at peak systole and mid-diastole. The hemodynamic data were statistically analyzed to evaluate correlations between FEVAR, BEVAR, and chEVAR, focusing on targeted visceral arteries. Results: Only slight differences were observed regarding RRT, OSI, and TAWSS between FEVAR and BEVAR, whereas the chEVAR group demonstrated a marked deviation from both. In FEVAR, the postoperative helical flow structures appeared more compact, while in BEVAR they were more developed and exhibited a more rotational configuration. The LNH of the visceral vessel patterns exhibited similar qualitative features across groups. Regarding TAWSS, higher values were found in BEVAR, whereas chEVAR showed the lowest. Conclusions: FEVAR, BEVAR, and chEVAR improved postoperative blood flow characteristics toward near-physiological conditions, reducing undesired flow patterns and recirculation zones. FEVAR showed more stable visceral flow, and BEVAR demonstrated higher flow rates and fewer recirculation zones, while chEVAR exhibited more streamlined visceral artery flow with reduced regurgitation at bridging stent entries. Despite variations, all approaches effectively preserved visceral artery perfusion.

Abdominal aortic aneurysm (AAA) is a life-threatening vascular condition that requires regular imaging and follow-ups to prevent fatal outcomes. While accurate diagnosis and selecting treatment strategies depend on aortic segmentation to assess disease progression, manual segmentation is time-consuming, prone to inter-observer variability, and can stall the clinical workflow. For the automatic aorta segmentation several deep learning methods have been proposed with high accuracy. However, their reliance on large annotated databases limits their applicability. To this end, self-supervised learning approaches have been developed to alleviate the need for manual labels during training. In CT imaging, Hounsfield Units (HU) correspond to specific anatomical structures, such as bones and soft tissues, based on their intensity ranges. In this paper, we exploit this property to effectively pre-train a Deep Learning segmentation model using the proposed Intensity Guided Masking (IGM) where we occlude regions within specific intensity ranges in the CT image and aim at predicting/reconstructing the masked area. Next, the pre-trained encoder is integrated into a SwinUNETR model, fine-tuned on manually labeled CT images, and evaluated for aortic structure segmentation. Our proposed method has been evaluated on both a public and a private dataset achieving DSC of 91.20% and 85% and ASSD of 0.05mm and 0.04mm, respectively and outperforming both state-of-the-art supervised baselines and pre-training based methods. The code will be released upon publication at https://github.com/theoVag/SwinUNETR-IGM.Clinical relevance— Our method improves aortic segmentation accuracy in CT imaging while reducing reliance on large annotated datasets, enhancing efficiency in vascular condition assessment such as detecting or quantifying abdominal aortic aneurysms.

Background: In recent years, more and more numerical tools have been utilized in medicine in or-der to assist the evaluation and decision-making processes for complex clinical cases. Towards this direction, Finite Element Models (FEMs) have emerged as a pivotal tool in medical research, particularly in simulating and understanding the complex fluid and structural behaviors of the circulatory system. Furthermore, this tool can be used for the calculation of certain risks regarding the function of the blood vessels. Methods: The current study developed a computational tool utilizing the finite element method in order to numerically evaluate stresses in aortas with abdominal aneurysms and provide the necessary data for the creation of a patient-specific digital twin of an aorta. More specifically, 12 different cases of aortas with abdominal aneurysms were examined and evaluated. Results: The first step was the 3D reconstruction of the aortas trans-forming the DICOM file into 3D surface models. Then, a finite element material model was developed simulating accurately the mechanical behavior of aortic walls. Conclusions: Through the results of these finite element analyses the values of tension, strain, and displacement were quantified and a rapid risk assessment was provided revealing that larger aneurysmatic regions elevate the risk of aortic rupture with some cases reaching an above 90% risk.

Pathophysiological conditions in arteries, such as stenosis or aneurysms, have a great impact on blood flow dynamics enforcing the numerical study of such pathologies. Computational fluid dynamics (CFD) could provide the means for the calculation and interpretation of pressure and velocity fields, wall stresses, and important biomedical factors in such pathologies. Additionally, most of these pathological conditions are connected with geometric vessel changes. In this study, the numerical solution of the 2D flow in a branching artery and a multiscale model of 3D flow are presented utilizing CFD. In the 3D case, a multiscale approach (3D and 0D–1D) is pursued, in which a dynamically altered velocity parabolic profile is applied at the inlet of the geometry. The obtained waveforms are derived from a 0D–1D mathematical model of the entire arterial tree. The geometries of interest are patient-specific 3D reconstructed abdominal aortic aneurysms after fenestrated (FEVAR) and branched endovascular aneurysm repair (BEVAR). Critical hemodynamic parameters such as velocity, wall shear stress, time averaged wall shear stress, and local normalized helicity are presented, evaluated, and compared.

Background: Fenestrated (FEVAR) and chimney (ChEVAR) endovascular aortic repair have been applied in anatomically suitable complex aortic aneurysms. However, local hemodynamic changes may occur after repair. This study aimed to compare FEVAR's and ChEVAR's hemodynamic properties, focusing on visceral arteries. Methods: Preoperative and postoperative computed tomography angiographies have been used to reconstruct patient-based models. Data of 3 patients, for each modality, were analyzed. Following geometric reconstruction, computational fluid dynamics simulations were used to extract near-wall and intravascular hemodynamic indicators, such as pressure drops, velocity, wall shear stress, time averaged wall shear stress, oscillatory shear index, relative residence time, and local normalized helicity. Results: An overall improvement in hemodynamics was detected after repair, with either technique. Preoperatively, a disturbed prothrombotic wall shear stress profile was recorded in several zones of the sac. The local normalized helicity results showed a better organization of the helical structures at postoperative setting, decreasing thrombus formation, with both modalities. Similarly, time averaged wall shear stress increased and oscillatory shear index decreased postoperatively, signaling nondisturbed blood flow. The relative residence time was locally reduced. The flow in visceral arteries tended to be more streamlined in ChEVAR, compared to evident recirculation regions at renal and superior mesenteric artery fenestrations (P 1/4 0.06). Conclusions: ChEVAR and FEVAR seem to improve hemodynamics toward normal values with a reduction of recirculation zones in the main graft and aortic branches. Visceral artery flow comparison revealed that ChEVAR tended to present lower recirculation regions at parallel grafts' entries while FEVAR showed less intense flow regurgitation in visceral stents.

An intraluminal thrombus (ILT) is present in the majority of abdominal aortic aneurysms, playing a crucial role in their growth and rupture. Although most computational studies do not include the ILT, in the present study, this is taken into account, laying out the whole simulation procedure, namely, from computed tomography scans to medical image segmentation, geometry reconstruction, mesh generation, biomaterial modeling, finite element analysis, and post-processing, all carried out in open software. By processing the tomography scans of a patient's aneurysm before and after rupture, digital twins are reconstructed assuming a uniform aortic wall thickness. The ILT and the aortic wall are assigned different biomaterial models; namely, the first is modeled as an isotropic linear elastic material, and the second is modeled as the Mooney-Rivlin hyperelastic material as well as the transversely isotropic hyperelastic Holzapfel-Gasser-Ogden nonlinear material. The implementation of the latter requires the designation of local Cartesian coordinate systems in the aortic wall, suitably oriented in space, for the proper orientation of the collagen fibers. The composite aneurysm geometries (ILT and aortic wall structures) are loaded with normal and hypertensive static intraluminal pressure. Based on the calculated stress and strain distributions, ILT seems to be protecting the aneurysm from a structural point of view, as the highest stresses appear in the thrombus-free areas of the aneurysmal wall.

The mechanical stresses and strains are examined, in ascending thoracic aortic aneurysm (aTAA) models, in a patient-specific aTAA as well as in healthy thoracic aortic models, via Finite Element Analysis. The aneurysms are assumed spherical, 1.5 mm thick, with diameters between 47 mm and 80 mm, eccentrically positioned. The geometry and wall thickness distribution of the aorta along its length are based on open literature data for an average patient age of 66.25 years, accounting for the Body Surface Area (BSA) parameter. The vessel wall material is assumed isotropic and incompressible, with its Young's modulus varying with the aneurysm diameter and the applied intraluminal pressure (120 mmHg to 240 mmHg). In the aTAAs, peak stresses were found to increase nonlinearly with aneurysm diameter (for a given pressure) tending to reach a plateau, appearing at the proximal area of the aneurysm, whereas lower stresses were found at its distal part and even smaller at the aneurysm maximum diameter. Regarding the patient-specific aTAA model, the peak stresses appeared at the distal part of the aneurysm where a tear of the intima layer was detected during surgical intervention. Peak strains exhibited for each pressure a maximum at a certain aneurysm diameter beyond which they dropped so that essentially the vessel wall's distensibility was thus reduced. Examining more than 100 geometry cases and employing a failure stress criterion, the rupture diameter thresholds were estimated to be 65, 52.5, 50 and 47.5 mm for a pressure of 120, 160, 200 and 240 mmHg respectively.

The aim of this study was to create a repository consisting of 3D surface models of abdominal aortic aneurysms (AAA) before and after endovascular aneurysm repair (EVAR). Computed tomography scans of 14 patients were utilized for this purpose. The workflow involved segmenting and reconstructing the medical images using Mimics software, along with several post-processing steps for surface refinement. The AAA cases encompassed the suprarenal abdominal aorta, including the celiac axis, superior mesenteric artery, and renal arteries, as well as the infrarenal abdominal aorta, including the aortic bifurcation and the common iliac arteries. The collection of patient-specific 3D AAA models will aid in the creation of virtual patient cohorts using statistical shape modeling and machine/deep learning algorithms. These models will help identify correlations between nonstandard morphometrics and clinical events, such as AAA rupture and post-EVAR complications.

Background: Carotid endarterectomy (CEA) remains the first-line treatment option of symptomatic and asymptomatic carotid stenosis, while stenting (CAS) is reserved for selected patients at high surgical risk. Here, we compare the vascular remodeling process in CEA-and CAS-treated patients with respect to morphological and hemodynamic features, because of their possible engagement in carotid atherosclerosis. Methods: Twelve (12) patients were included, half with patched CEA and half with CAS. Pre-and post-operative 3D image-based models of the carotid bifurcation were anatomically characterized in terms of flare, tortuosity, and curvature. Individual computational fluid dynamics simulations allowed to quantify the postoperative hemodynamic milieu in terms of (1) wall shear stress and (2) helical flow. Results: Carotid flare increased in all cases, but a more marked increase emerged after CEA compared to CAS. Tortuosity and curvature increased after CEA but decreased after CAS. CEA patients presented with significantly higher postoperative tortuosity than CAS patients. CEA was associated with a worse (non-statistically significant) score in all flow disturbance indicators vs. CAS. Conclusion: The increased flare and tortuosity of the carotid bifurcation after CEA vs. CAS is a marked difference in the vascular remodeling process between the two modalities. CAS seems to induce a less pro-restenosis hemodynamic environment compared to CEA. The emerged differences stimulate further analysis on a larger cohort with long-term outcomes, to shed light on the clinical impact of the observations.

The study presents a generalized analytical solution of the laminar, oscillatory, creeping flow of an incompressible Newtonian fluid in a porous circular pipe with spatiotemporally periodic suction/injection at the wall. The analytical solution is examined for a variety of values of the dimensionless parameters, namely the Womersley number and the dimensionless suction/injection number.

Hybrid endograft combinations of two or more different types of covered stents are rarely reported to treat complex abdominal aortic aneurysm cases or primary and secondary endoleaks. Clinical and laboratory data regarding the clinical efficacy and mechanical stability of such combinations are lacking. Based on a recently published case report, we describe and comment on the hemodynamic profile of a representative simulated hybrid case of AFX and Nitinol-based proximal cuff and support the stability of this combination in non-angulated cases.

This work presents the creation of geometric surface models representing the heart chambers and the aorta for two patient specific cases. The first one concerns an acute ascending aortic aneurysm in the anterior Valsalva sinus and the second one a normal aorta for comparison reasons. The surface modelling was implemented in a medical image reconstruction software (Materialise Mimics), based on the computed tomography scans of the patients. For each case, the two atriums and ventricles, the ascending aorta, aortic arch and descending aorta, the pulmonary artery and the superior vena cava were also reconstructed and modelled. Special attention is given to the morphology of the vessels and the heart chambers that are in contact with the ascending aortic aneurysm, due to the acute aneurysmal extension of the Valsalva sinus. A comparison of the non-aneurysmal and the aneurysmal models is necessary to infer whether this disease affects the geometries and/or other vital organs that come in contact with the aortic aneurysm. Special care is given to the surfaces’ smoothing process to preserve the morphology of the structures, avoiding any deviations from the actual geometries of the corresponding vessels and heart chambers.

Endovascular aneurysm repair (EVAR), despite its advantages over abdominal aortic aneurysm (AAA) open surgery, still presents risks of failure linked to Endograft (EG) migration. We here explore the link between intravascular blood flow features and Displacement Forces (DFs) acting on the EG. DFs are inversely associated with the amount of helical flow within the EG.

Background: The bifurcated AFX (Endologix, Inc, Irvine, CA, USA) aortic stent-graft is the sole unibody endograft for the management of Abdominal Aortic Aneurysms (AAA). In order to improve the AFX central sealing and clinical efficacy in challenging cases, a replacement of the central chromium-cobaltium AFX extension with a Nitinol-based proximal aortic cuff has been suggested. Yet, comparative data regarding the hemodynamic performance of this design is missing. Aim of this study was to compare the displacement forces (DF) acting on the hybrid AFX-Endurant design, with the classic AFX and Endurant endografts, in angulated and non-angulated cases based on patient-specific Computational Fluid Dynamics (CFD) simulations. Methods: 3D endograft models of 11 treated AAA cases were reconstructed from Computed Tomography Angiography (CTA) imaging data: 5 cases of AFX, 3 cases of the combination AFX-Endurant and 3 cases of the classic Endurant design. The DF on the main-body, the iliac limbs, and the entire stent-graft was calculated by processing the velocity and pressure fields generated by pulsatile CFD simulations. Results: The range of total DF (acting on the whole endograft structure) in the AFX, hybrid AFX-Endurant and Endurant group was 2.5-5.2N, 2.0-5.9N and 1.9-2.9N respectively, with the maximum total DF being lower for Endurant. The DF on the main-body of the classic and hybrid AFX cases were higher than the right and left iliac limbs (2.5-4.9N vs. 0.6-5.3N and 0.7-3.6N respectively). Conversely, the DF on the main-body of the Endurant cases was comparable to the force exerted on the right and left limbs. When separating the cases with respect to their neck angulation, the DF on all endograft parts (main-body, limbs) and on the endograft as a whole were lower for the hybrid AFX-Endurant group compared to the classic AFX and Endurant groups, for cases with almost straight neck. Conclusion: The off-label use of the hybrid AFX-Endurant stent-graft does not seem superior to the conventional AFX or Endurant endografts in angulated cases but was associated with lower DF than AFX or Endurant in non-angulated cases. The clinical value and utility of these findings remain to be elucidated.

A wall mechanics study is performed on two human aortic models, reconstructed from computed tomography (CT) image data using the Materialise Mimics software. The first model represents a rare ascending thoracic aortic aneurysm (aTAA) case with an excessive aortic ballooning that has displaced the cardiac cavities, and the second one a normal case free of cardiovascular diseases. Special attention was paid for the reconstruction of realistic models that do not deviate from the original data. The study presents the workflow from medical imaging data to structural simulation with the use of various software, aiming to examine the stress state of a normal aorta and an aneurysmal one (both patient specific) under a range of systolic blood pressure loads. Using the FEBio software, the effective (Lagrange) strain and the effective stress (von Mises) distributions are calculated for assessing the risk of rupture or dissection of the aorta.

The study addresses the oscillating magnetohydrodynamic (MHD) Stokes flow between two parallel plates with periodic reabsorption both spatially and temporally. Two cases are distinguished by applying either (1) transverse or (2) parallel external magnetic field. Analytical solutions of velocity and pressure are derived for both cases and the effect of Womersley and Hartmann number, and the absorption coefficient is examined. The study generalizes existing literature on analytic MHD Stokes flow solutions accounting for periodic boundary conditions both in time and space. The non-oscillating non-MHD Stokes flow in a porous channel (available in the literature) is proven to be a limit of the analytic solution introduced here. The MHD effects are noticeable in flows oscillating with low or moderate frequency but are barely detectable in high-frequency flows even in the presence of strong magnetic fields.

Introduction: Carotid endarterectomy (CEA) and carotid artery stenting (CAS) are interventional therapeutic alternatives for the treatment of carotid stenosis (CS), which is partially triggered by atherogenic hemodynamic conditions regulated from the bifurcation morphology. The predictive potential of morphological and hemodynamic features was recently examined in the post-CEA setting, suggesting that arteriotomy repair should avoid a large widening of the carotid bulb, which is linked to restenosis via the generation of flow disturbances [1,2]. Here, we study the impact of CAS vs. CEA with patch-plasty on carotid bifurcation geometry and hemodynamics, supported by patient-based computational simulations. Methods: After digitally recording CT data of patients treated with CAS (n=2) or CEA (n=2), the 3D carotid bifurcation geometries were reconstructed. As geometry shapes the flow, which is in turn implied in the restenosis process, a centerline-based geometric analysis was carried out on the reconstructed geometries (Figure 1). Hemodynamics-informed geometric descriptors were calculated, i.e., carotid flare (a measure of the carotid bulb expansion) and tortuosity, as suggested elsewhere [2-3]. Complementary, computational fluid dynamics simulations were performed to determine the extent of luminal surface area exposed to low and oscillatory wall shear stress, a hemodynamic condition widely recognized as "disturbed shear", with acknowledged atherogenic [4] and restenosis risk potential [2]. Results: A different reshaping of the carotid bifurcation was observed as a consequence of CAS vs. CEA. In general, stent implantation led to reduced tortuosity, while no significant variation was observed for flare with respect to the pre-operative geometry. Conversely, CEA led to a significant increase of flare and to minor variations of tortuosity. As for hemodynamics, larger areas at the luminal surface exposed to disturbed shear were observed in stented cases (Figure 2). Conclusion: CAS and CEA reshape the carotid bifurcation in a different way, suggesting that different restenosis trajectories are possible in the long term. The larger disturbed shear area in CAS cases might be ascribed to the decrease in tortuosity [2-3], although the complex interaction between geometry and the underlying disturbed shear will be subject of future investigations. The present results confirm very recent findings [2] suggesting that geometric and hemodynamic analyses hold potential for the virtual exploration of personalized post-operative scenarios, providing useful indications on (1) the best treatment strategy (e.g., CEA vs. CAS), and (2) the stratification of post-intervention restenosis risk. Disclosure: Nothing to disclose