Deep learning-based segmentation of abdominal aortic aneurysms and intraluminal thrombus in 3D ultrasound images.

Ultrasound (US)-based patient-specific rupture risk analysis of abdominal aortic aneurysms (AAAs) has shown promising results. Input for these models is the patient-specific geometry of the AAA. However, segmentation of the intraluminal thrombus (ILT) remains challenging in US images due to the low ILT-blood contrast. This study aims to improve AAA and ILT segmentation in time-resolved three-dimensional (3D + t) US images using a deep learning approach. In this study a "no new net" (nnU-Net) model was trained on 3D + t US data using either US-based or (co-registered) computed tomography (CT)-based annotations. The optimal training strategy for this low-contrast data was determined for a limited dataset. The merit of augmentation was investigated, as well as the inclusion of low-contrast areas. Segmentation results were validated with CT-based geometries as the ground truth. The model trained on CT-based masks showed the best performance in terms of DICE index, Hausdorff distance, and diameter differences, covering a larger part of the AAA. With a higher accuracy and less manual input the model outperforms conventional methods, with a mean Hausdorff distance of 4.4 mm for the vessel and 7.8 mm for the lumen. However, visibility of the lumen-ILT interface remains the limiting factor, necessitating improvements in image acquisition to ensure broader patient inclusion and enable rupture risk assessment of AAAs in the future.

Relationship Between Intraluminal Thrombus Volume and Circulating ADAMTS-13 Activity in Abdominal Aortic Aneurysms.

Introduction: Abdominal aortic aneurysms (AAAs) with intraluminal thrombus (ILT) are suggested to be more prone to rupture than AAAs without. Prior studies indicate that the von Willebrand factor (vWf) plays a role in the formation of ILT since a positive correlation between ILT volume and vWf has been shown. vWf mediates the tethering of platelets at sites of endothelial injury, and the protease ADAMTS-13 cleaves larger forms of vWf, thus counteracting the thrombosis cascade and maintaining haemostatic balance. When investigating the largest quantifiable thrombus in the human body, it was hypothesised that circulating ADAMTS-13 activity may be associated with ILT size in patients with AAA and the aim was to explore this potential relationship using 3D contrast enhanced ultrasound (3D-CEUS) for ILT volume determination. Report: In this retrospective, exploratory study, 60 patients with AAA were evaluated, and the association between ILT volume and thickness and ADAMTS-13 was estimated using 3D-CEUS. ADAMTS-13 activity was measured in plasma samples obtained the same day. No association between ILT volume (r = -0.03, p = 0.84) or ILT thickness (r = 0.02, p = 0.87) and ADAMTS-13 activity was found. Likewise, when subdividing the group into lowest and highest 50% of ADAMTS-13 activity, the half with the lowest ADAMTS-13 activity (mean ILT volume ±standard deviation [SD]: 32 ± 34 mL) did not differ from the half with the highest ADAMTS-13 activity (43 ± 24 mL) when comparing ILT volume (p = 0.172, F = 2.95) and thickness (p = 0.070). Discussion: After evaluating the largest quantifiable intraluminal thrombus in the vasculature, it was concluded that, surprisingly, circulating ADAMTS-13 activity seems unrelated to ILT formation in AAA.

Relationship between the intravascular enhancement sign on three-dimensional T1-weighted turbo spin echo and intraluminal thrombus in middle cerebral artery atherosclerosis.

PURPOSE: To investigate the association between the intravascular enhancement sign (IVES) and intraluminal thrombus (ILT) detected by high-resolution magnetic resonance vessel wall imaging (HR-VWI) in patients with middle cerebral artery (MCA) atherosclerosis. METHOD: The data of patients who underwent HR-VWI between May 2021 and May 2023, including clinical information, the number of IVES vessels, stenosis degree, ILT, plaque features on 3D T1-weighted turbo spin echo sequences, and signal intensity ratio (SIR) on 3D time-of-flight magnetic resonance angiography, were retrospectively analyzed. Correlation and logistic regression analyses were performed. RESULTS: A total of 194 MCA plaques were identified in 132 patients (103 [53 %] on the left). Atherosclerosis with, relative to without, ILT was associated with a higher incidence of ischemic events, higher plaque enhancement and stenosis degrees, more vessels with IVES, and lower remodeling ratio, lumen area, wall area, total vessel area, and SIR. Multivariate logistic regression analysis showed significant and independent associations of the number of IVES vessels (OR = 1.089; 95 % CI [1.013-1.170]; P = 0.020) and SIR (OR = 0.007; 95 % CI [0.0004-0.124]; P < 0.001) with ILT. The number of vessels with the IVES (AUC = 0.81, 95 % CI [0.75-0.87]; P < 0.001) and SIR (AUC = 0.88, 95 % CI [0.82-0.94]; P < 0.001) sufficiently diagnosed ILT, and the AUC of the combination of the IVES and SIR was 0.89 (95 % CI [0.84-0.94]; P < 0.001). CONCLUSION: The number of IVES vessels and SIR are independent risk factors for ILT. They may provide new monitoring targets for stroke prevention in patients with atherosclerotic stenosis.

Computational Study of Abdominal Aortic Aneurysm Walls Accounting for Patient-Specific Non-Uniform Intraluminal Thrombus Thickness and Distinct Material Models: A Pre- and Post-Rupture Case.

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.

Relative Thrombus Burden Ratio Reveals Overproportioned Intraluminal Thrombus Growth-Potential Implications for Abdominal Aortic Aneurysm.

Background: An intraluminal, non-occlusive thrombus (ILT) is a common feature in an abdominal aortic aneurysm (AAA). This study investigated the relative progression of ILT vs. AAA volume using a novel parameter, the so-called thrombus burden ratio (TBR), in non-treated AAAs. Parameters potentially associated with TBR progression were analyzed and TBR progression in large vs. small and fast- vs. slow-growing AAAs was assessed. Methods: This retrospective, single-center study analyzed sequential contrast-enhanced computed tomography angiography (CTA) scans between 2009 and 2018 from patients with an AAA before surgical treatment. Patients' medical data and CTA scans were analyzed at two given time points. The TBR was calculated as a ratio of ILT and AAA volume, and relative TBR progression was calculated by normalization for time between sequential CTA scans. Spearman's correlation was applied to identify morphologic parameters correlating with TBR progression, and multivariate linear regression analysis was used to evaluate the association of clinical and morphological parameters with TBR progression. Results: A total of 35 patients were included. The mean time between CT scans was 16 ± 15.9 months. AAA volume progression was 12 ± 3% and ILT volume progression was 36 ± 13%, resulting in a TBR progression of 11 ± 4%, suggesting overproportioned ILT growth. TBR progression was 0.8 ± 0.8% per month. Spearman's correlation verified ILT growth as the most relevant parameter contributing to TBR progression (R = 0.51). Relative TBR progression did not differ significantly in large vs. small and fast- vs. slow-growing AAAs. In the multivariate regression analysis, none of the studied factors were associated with TBR progression. Conclusion: TBR increases during AAA development, indicating an overproportioned ILT vs. AAA volume growth. The TBR may serve as a useful parameter, as it incorporates the ILT volume growth relative to the AAA volume, therefore combining two important parameters that are usually reported separately. Yet, the clinical relevance in helping to identify potential corresponding risk factors and the evaluation of patients at risk needs to be further validated in a larger study cohort.

CTA-Based Radiomics and Area Change Rate Predict Infrarenal Abdominal Aortic Aneurysms Patients Events: A Multicenter Study.

RATIONALE AND OBJECTIVES: Clinical assessment of abdominal aortic aneurysm (AAA) intervention and rupture risk relies primarily on maximum diameter, but studies have shown that sole dependence on diameter has limitations. CTA-based radiomics, aneurysm and lumen area change rates (AACR, LACR) are measured to predict potential AAA events. MATERIALS AND METHODS: Between January 2017 and November 2022, 260 AAA patients from four centers who underwent two preoperative CTA examinations were included in this retrospective study. The endpoint event is defined as AAA rupture or repair. Patients were categorized into event and no-event groups based on the occurrence of endpoint event during follow-up. AACR and LACR were assessed using baseline and follow-up CTA, with radiomics features extracted from the baseline images. C-statistics and the Kaplan-Meier analysis were used to evaluate the predictive performance. RESULTS: A total of 193 eligible infrarenal AAA patients were included, 176 (91.2%) were man and 17 (8.8%) were woman. The median follow-up was 33.4 (14.2, 57.4) months. Seven models were constructed, comprising the aneurysm-based Radscore model, lumen-based Radscore model, intraluminal thrombus (ILT)-based Radscore model, AACR model, LACR model, clinical model (including high-density lipoprotein, D-dimer, and baseline aneurysm diameter), and a merged model. On the external validation set, the C-index of seven models were 0.713 (0.574-0.853), 0.642 (0.499-0.786), 0.727 (0.600-0.854), 0.619 (0.484-0.753), 0.680 (0.530-0.830), 0.690 (0.557-0.824) and 0.760 (0.651-0.869), in that order. In the Kaplan-Meier analysis, the merged model was best-divided patients into high/low-risk groups with Log-rank p < 0.0001. The AARC and LARC between non-event and event groups have significant differences (AACR: 1.4 cm2/y vs. 2.3 cm2/y, p < 0.0001; LACR: 0.3 cm2/y vs. 1.1 cm2/y, p < 0.0001). CONCLUSION: CTA-based radiomics, AACR and LACR have good predictive value for outcome event in infrarenal AAA patients.

Intraluminal Thrombus of the Extracranial Cerebral Arteries in Acute Ischemic Stroke: Manifestations, Treatment Strategies, and Outcome.

Background: Intraluminal thrombus (ILT) of the cervical arteries is an uncommon finding that can lead to acute or recurrent ischemic stroke. Currently, antithrombotic therapy in the form of antiplatelet and/or anticoagulation is considered the mainstay of treatment, but evidence of which one has a better outcome is lacking. Methods: A retrospective cohort study included 28 patients diagnosed with acute stroke or transient ischemic attack with ILT of the extracranial arteries from 2013 to 2022. The primary efficacy outcome was assessed as recurrent stroke, and the primary safety outcome was assessed as hemorrhagic complications. Secondary outcomes were assessed as the resolution of thrombi by CT angiography (CTA) and clinical improvement by the Modified Rankin Scale (mRS) and NIH Stroke Scale (NIHSS). Results: Out of 28 patients, more than half (57.1%; n = 16) were males with a mean age of 57.8 ± 9.5 years and an average BMI of 26.9 ± 4.5 kg/m2. As initial treatment, twenty-four patients received anticoagulation and four received antiplatelet agents. Recurrent strokes were found in four patients (14.29%), and all were initially treated with anticoagulation. One patient in the anticoagulation group had a significant retroperitoneal hemorrhage. None of the patients in the antiplatelets group had a recurrent stroke or bleeding event. Initial treatment with antiplatelet agents significantly improved the NIHSS on day 7 (P = 0.017). A significant improvement in NIHSS on day 90 was observed in the anticoagulant group (P = 0.011). In the follow-up CTA performed on 24 patients, 18 (75%) showed complete resolution (3 out of 3 (100%) in the antiplatelet group and 15 out of 21 (71.43%) in the anticoagulant group). Conclusion: Initial treatment with anticoagulants improves neurologic outcomes in patients with ILT-induced acute ischemic stroke but carries the risk of recurrent stroke and bleeding. However, initial treatment with dual antiplatelet agents appears to have comparable efficacy without sequelae, particularly in atherosclerosis-induced ILT.

Analyzing the contribution of vasa vasorum in oxygenation of the aneurysmal wall: A computational study.

The mechanisms of abdominal aortic aneurysm (AAA) formation and rupture are controversial in the literature. While the intraluminal thrombus (ILT) plays a crucial role in reducing oxygen flux to the tissue and therefore decreasing the aortic wall strength, other physiological parameters such as the vasa vasorum (VV) oxygen flow and its consumption contribute to altered oxygenation responses of the arterial tissue as well. The goal of this research is to analyse the importance of the aforementioned parameters on oxygen delivery to the aneurysmal wall in a patient-specific AAA. Numerical simulations of coupled blood flow and mass transport with varying levels of VV concentration and oxygen reaction rate coefficient are performed. The hypoperfusion of the adventitial VV and high oxygen consumption are observed to have critical effects on reducing aneurysmal tissue oxygen supply and can therefore exacerbate localized oxygen deprivation.

Acute phase supra-aortic intraluminal thrombus signal changes on magnetic resonance angiography: A case series: Intraluminal thrombus signal changes on MRA.

BACKGROUND AND OBJECTIVES: Intraluminal thrombus (ILT) is a relatively rare cause of stroke. MRI/MRA is increasingly used for stroke patients eligible for acute treatment. Radiological ILT characteristics have never been studied systematically on MRA. We aimed to analyse signal changes and other radiological characteristics of ILT in the acute phase on MRA in a case series of ILT patients. MATERIALS AND METHODS: Consecutive stroke patients registered in our stroke database between January 2013 and September 2022 were screened for supra-aortic ILT on MRA, in whom MRA was the first supra-aortic vessel imaging performed. Twelve patients were included for analysis. Radiological analysis on MRA included ILT localisation, diameter of the free-floating ILT component, total ITL length, degree of stenosis caused by ILT, and ILT signal intensity. RESULTS: Median age was 65 years and 92% were men. Median time interval between stroke onset and MRA was 0.5 days. Atherosclerosis was the underlying ILT aetiology in half of the patients. The most frequent ILT localisation was the internal carotid artery, always involving the C1 segment. Median ILT diameter was 4.35 mm, median length 20.9 mm, median stenosis 65%, and with a homogeneous hypointensity of the ILT in 67% and a mixed hypo-hyperintensity in 33% (with ILT showing central hyperintensity surrounded by peripheral hypointensity). DISCUSSION: When observed on MRA, ILT showed a homogeneous hypointensity in two-thirds and a mixed hypo-hyperintensity in one third of patients. In future studies, follow-up MRA scans should be performed to analyse whether these signal changes are time-related or influenced by antithrombotic treatment for ILT.

Association of preoperative aneurysmal wall enhancement with relief of chronic headache after surgical clipping of unruptured intracranial aneurysms.

OBJECTIVE: To investigate the association between chronic headache outcome and aneurysmal wall enhancement (AWE) on high-resolution vessel wall imaging (HR-VWI) in patients with unruptured intracranial aneurysms (UIAs) who underwent microsurgical clipping. METHODS: Two hundred seventy-four UIA patients were retrospectively analyzed. Patients were grouped according to presence of AWE. AWE was subclassified as focal or uniform. Clinical and imaging data were recorded. Headache was evaluated using the 10-point numerical rating scale and Headache Impact Test-6 before and 6 months after surgery. RESULTS: The proportions of patients reporting chronic headache in the no AWE, focal wall enhancement (FWE), and uniform wall enhancement (UWE) groups were 5.7%, 24.8%, and 41.8%, respectively. All patients in the UWE group who reported headache before surgery experienced headache improvement after surgery. Decrease in headache severity was greater in the UWE group than in the FWE group. Multivariate binary logistic regression showed that FWE (odds ratio (OR) 0.490; 95% confidence interval (CI), 0.262-0.917; p = 0.026) and small intraluminal thrombus (OR 0.336; 95% CI, 0.142-0.795; p = 0.013) were independent factors protective against preoperative headache. FWE (OR 0.377; 95% CI, 0.195-0.728; p = 0.004) and small intraluminal thrombus (OR 0.235; 95% CI, 0.088-0.630; p = 0.004) were independent predictors of no headache relief after surgery. CONCLUSIONS: AWE on HR-VWI is associated with relief of chronic headache after surgical clipping in patients with UIAs. Incidence of chronic headache was highest in patients exhibiting UWE. These patients also experienced the greatest improvement in headache after surgical clipping. CLINICAL RELEVANCE STATEMENT: This study revealed that high-resolution vessel wall imaging can demonstrate aneurysmal wall plaque and intraluminal thrombus, which may be prognostic imaging markers for chronic headache in patients with unruptured intracranial aneurysms. KEY POINTS: • Aneurysmal wall enhancement may be associated with chronic headache. • Incidence of chronic headache was highest in patients with aneurysms exhibiting uniform wall enhancement. • Patients with aneurysms exhibiting uniform wall enhancement experienced the greatest improvement in headache after clipping.

Partially thrombosed giant basilar artery aneurysm with attenuated contrast enhancement of the intraluminal thrombus on vessel wall MRI after flow diversion treatment: illustrative case.

BACKGROUND: The effect of vessel wall magnetic resonance imaging (VW-MRI) enhancement in partially thrombosed aneurysms has previously indicated aneurysmal instability and a rupture risk. However, whether the contrast effect of the wall changes before or after flow diversion treatment is still under investigation. OBSERVATIONS: The authors report a case of a partially thrombosed basilar artery aneurysm that increased in size over a short period, worsened brainstem compression symptoms, and was treated with a flow diverter stent with good results. In this case, VW-MRI after surgery showed a reduced contrast effect on the intraluminal thrombus within the aneurysm. The aneurysm thrombosed and markedly regressed over the next 5 months, with remarkable improvement in the brainstem compression symptoms. LESSONS: This finding on VW-MRI may indicate an attenuation of neovascularization in the thrombus wall and be a sign of aneurysm stabilization.

Assessing Abdominal Aortic Aneurysm Progression by Using Perivascular Adipose Tissue Attenuation on Computed Tomography Angiography.

OBJECTIVE: Recent studies have highlighted the active and potential role of perivascular adipose tissue (PVAT) in atherosclerosis and aneurysm progression, respectively. This study explored the link between PVAT attenuation and abdominal aortic aneurysm (AAA) progression using computed tomography angiography (CTA). MATERIALS AND METHODS: This multicenter retrospective study analyzed patients with AAA who underwent CTA at baseline and follow-up between March 2015 and July 2022. The following parameters were obtained: maximum diameter and total volume of the AAA, presence or absence of intraluminal thrombus (ILT), maximum diameter and volume of the ILT, and PVAT attenuation of the aortic aneurysm at baseline CTA. PVAT attenuation was divided into high (> -73.4 Hounsfield units [HU]) and low (≤ -73.4 HU). Patients who had or did not have AAA progression during the follow-up, defined as an increase in the aneurysm volume > 10 mL from baseline, were identified. Kaplan-Meier and multivariable Cox regression analyses were used to investigate the association between PVAT attenuation and AAA progression. RESULTS: Our study included 167 participants (148 males; median age: 70.0 years; interquartile range: 63.0-76.0 years), of which 145 (86.8%) were diagnosed with AAA accompanied by ILT. Over a median period of 11.3 months (range: 6.0-85.0 months), AAA progression was observed in 67 patients (40.1%). Multivariable Cox regression analysis indicated that high baseline PVAT attenuation (adjusted hazard ratio [aHR] = 2.23; 95% confidence interval [CI], 1.16-4.32; P = 0.017) was independently associated with AAA progression. This association was demonstrated within the patients of AAA with ILT subcohort, where a high baseline PVAT attenuation (aHR = 2.23; 95% CI, 1.08-4.60; P = 0.030) was consistently independently associated with AAA progression. CONCLUSION: Elevated PVAT attenuation is independently associated with AAA progression, including patients of AAA with ILT, suggesting the potential of PVAT attenuation as a predictive imaging marker for AAA expansion.

Thrombosis in the pathogenesis of abdominal aortic aneurysm.

Background: Abdominal aortic aneurysms (AAAs) are a relatively common vascular pathology of the elderly with high morbidity potential. Irreversible degeneration of the aortic wall leads to lethal rupture if left untreated. Nearly all AAAs contain intraluminal thrombus (ILT) to a varying degree, yet the mechanisms explaining how thrombosis is disturbed in AAA are relatively unknown. This review examined the thrombotic complications associated with AAA, the impact of thrombosis on AAA surgical outcomes and AAA pathogenesis, and the use of antithrombotic therapy in the management of this disease. Methods: A literature search of the PubMed database was conducted using relevant keywords related to thrombosis and AAAs. Results: Thrombotic complications are relatively infrequent in AAA yet carry significant morbidity risks. The ILT can impact endovascular aneurysm repair by limiting anatomic suitability and influence the risk of endoleaks. Many of the pathologic mechanisms involved in AAA development, including hemodynamics, inflammation, oxidative stress, and aortic wall remodeling, contain pathways that interact with thrombosis. Conversely, the ILT can also be a source of biochemical stress and exacerbate these aneurysmal processes. In animal AAA models, antithrombotic therapies have shown favorable results in preventing and stabilizing AAA. Antiplatelet agents may be beneficial for reducing risks of major adverse cardiovascular events in AAA patients; however, neither antiplatelet nor anticoagulation is currently used solely for the management of AAA. Conclusions: Thrombosis and ILT may have detrimental effects on AAA growth, rupture risk, and patient outcomes, yet there is limited understanding of the pathologic thrombotic mechanisms in aneurysmal disease at the molecular level. Preventing ILT using platelet and coagulation inhibitors may be a reasonable theoretical target for aneurysm progression and stability; however, the practical benefits of current antithrombotic therapies in AAA are unclear. Further research is needed to demonstrate the extent to which thrombosis impacts AAA pathogenesis and to develop novel pharmacologic strategies for the medical management of this disease.

Effect of Intraluminal Thrombus Burden on the Risk of Abdominal Aortic Aneurysm Rupture.

Abdominal aortic aneurysm (AAA) is a critical health disorder, where the abdominal aorta dilates more than 50% of its normal diameter. Enlargement in abdominal aorta alters the hemodynamics and flow-induced forces on the AAA wall. Depending on the flow conditions, the hemodynamic forces on the wall may result in excessive mechanical stresses that lead to AAA rupture. The risk of rupture can be predicted using advanced computational techniques such as computational fluid dynamics (CFD) and fluid-structure interaction (FSI). For a reliable rupture risk assessment, formation of intraluminal thrombus (ILT) and uncertainty in arterial material properties should be taken into account, mainly due to the patient-specific differences and unknowns in AAAs. In this study, AAA models are computationally investigated by performing CFD simulations combined with FSI analysis. Various levels of ILT burdens are artificially generated in a realistic AAA geometry, and the peak effective stresses are evaluated to elucidate the effect of material models and ILT formation. The results indicate that increasing the ILT burden leads to lowered effective stresses on the AAA wall. The material properties of the artery and ILT are also effective on the stresses; however, these effects are limited compared to the effect of ILT volume in the AAA sac.

Intraluminal Thrombus Characteristics in AAA Patients: Non-Invasive Diagnosis Using CFD.

Abdominal aortic aneurysms (AAA) continue to pose a high mortality risk despite advances in medical imaging and surgery. Intraluminal thrombus (ILT) is detected in most AAAs and may critically impact their development. Therefore, understanding ILT deposition and growth is of practical importance. To assist in managing these patients, the scientific community has been researching the relationship between intraluminal thrombus (ILT) and hemodynamic parameters wall shear stress (WSS) derivatives. This study analyzed three patient-specific AAA models reconstructed from CT scans using computational fluid dynamics (CFD) simulations and a pulsatile non-Newtonian blood flow model. The co-localization and relationship between WSS-based hemodynamic parameters and ILT deposition were examined. The results show that ILT tends to occur in regions of low velocity and time-averaged WSS (TAWSS) and high oscillation shear index (OSI), endothelial cell activation potential (ECAP), and relative residence time (RRT) values. ILT deposition areas were found in regions of low TAWSS and high OSI independently of the nature of flow near the wall characterized by transversal WSS (TransWSS). A new approach is suggested which is based on the estimation of CFD-based WSS indices specifically in the thinnest and thickest ILT areas of AAA patients; this approach is promising and supports the effectiveness of CFD as a decision-making tool for clinicians. Further research with a larger patient cohort and follow-up data are needed to confirm these findings.

The study on the impact of AAA wall motion on the hemodynamics based on 4D CT image data.

Purpose: To analyze the effect of the physiological deformation of the vessel wall on the hemodynamics in the abdominal aortic aneurysm (AAA), this paper compared the hemodynamics in AAA based on the moving boundary (MB) simulation and the rigid wall (RW) simulation. Method: Patient-specific models were reconstructed to generate mesh based on four-dimensional computed tomography angiography (4D CT) data. The dynamic mesh technique was used to achieve deformation of the vessel wall, surface mesh and volume mesh of the fluid domain were successively remeshed at each time step. Besides, another rigid wall simulation was performed. Hemodynamics obtained from these two simulations were compared. Results: Flow field and wall shear stress (WSS) distribution are similar. When using the moving boundary method (MBM), mean time-averaged wall shear stress (TAWSS) is lower, mean oscillatory shear index (OSI) and mean relative residence time (RRT) are higher. When using the 10th and 20th percentile values for TAWSS and 80th and 90th percentile values for RRT, the ratios of areas with low TAWSS, high OSI and high RRT to the entire vessel wall are higher than those assuming the vessel as rigid. In addition, one overlapping region of low TAWSS, high OSI and high RRT by using the MBM is consistent with the location of thrombus obtained from the follow-up imaging data. Conclusion: The hemodynamics results by using the MBM reflect a higher blood retention effect. This paper presents a potential tool to assess the risk of intraluminal thrombus (ILT) formation based on the MBM.

Automatic Segmentation and Mechanical Characterisation of the Intraluminal Thrombus and Arterial Wall of Abdominal Aortic Aneurysms Using Time Resolved 3D Ultrasound Images.

OBJECTIVE: This study proposed a method for semi-automatic segmentation of abdominal aortic aneurysms (AAAs) and their intraluminal thrombus (ILT), based on time resolved 3D ultrasound (US), and validated results with computed tomography (CT). Mechanical properties of both wall and ILT were determined, and possible correlations with ILT size and blood pressure were investigated. METHODS: A semi-automatic segmentation algorithm was developed combining a star-Kalman approach with a 3D snake algorithm. The segmented geometries of both lumen and inner vessel wall were validated with both manual US based segmentations and CT based segmentations. Finally, the lumen and vessel wall distensibility and ILT compressibility were estimated and correlated with ILT size and blood pressure. RESULTS: For the vessel wall and lumen, the median Similarity Index (SI) was 92% (IQR 90, 94%) and 83% (IQR 75, 87%), respectively. The distensibility of the vessel wall could be determined in 37 of 40 cases and had a median value of 0.28 10-5 Pa-1 (IQR 0.18, 0.51 ×10-5). The median systolic to diastolic volume change of the ILT was determined successfully in 21 of 40 patients, and was -0.57% (IQR -1.1, 1.2%). The vessel and lumen distensibility showed a strong correlation with the systolic pressure (p < .010), rather than with the diastolic pressure. Lumen distensibility was strongly correlated with ILT thickness (p = .023). The performance of the semi-automatic segmentation algorithm was shown to be as good as the manual segmentations and highly dependent on the visibility of the ILT (limited contrast in seven patients and clutter in nine patients). CONCLUSION: This study has shown promising results for mechanical characterisation of the vessel, and ILT, including a correlation between distensibility, ILT size, and blood pressure. For future work, the inclusion rate needs to be increased by improving the image contrast with novel US techniques.

Features and risk factors of early intraluminal thrombus formation within the frozen elephant trunk stent graft.

OBJECTIVE: The frozen elephant trunk is a standard treatment method for aortic arch pathologies extending into the descending aorta. We previously described the phenomenon of early postoperative intraluminal thrombosis within the frozen elephant trunk. We investigated the features and predictors of intraluminal thrombosis. METHODS: A total of 281 patients (66% male, mean age 60 ± 12 years) underwent frozen elephant trunk implantation between May 2010 and November 2019. In 268 patients (95%), early postoperative computed tomography angiography was available to assess intraluminal thrombosis. RESULTS: The incidence of intraluminal thrombosis after frozen elephant trunk implantation was 8.2%. Intraluminal thrombosis was diagnosed early after the procedure (4.6 ± 2.9 days) and could be successfully treated with anticoagulation in 55% of patients. A total of 27% developed embolic complications. Mortality (27% vs 11%, P = .044) and morbidity were significantly higher in patients with intraluminal thrombosis. Our data showed a significant association of intraluminal thrombosis with prothrombotic medical conditions and anatomic slow flow features. The incidence of heparin-induced thrombopenia was higher in patients with intraluminal thrombosis (18% vs 3.3%, P = .011). Stent-graft diameter index, anticipated endoleak Ib, and degenerative aneurysm were significant independent predictors of intraluminal thrombosis. Therapeutic anticoagulation was a protective factor. Glomerular filtration rate, extracorporeal circulation time, postoperative rethoracotomy, and intraluminal thrombosis (odds ratio, 3.19, P = .047) were independent predictors of perioperative mortality. CONCLUSIONS: Intraluminal thrombosis is an underrecognized complication after frozen elephant trunk implantation. In patients with risk factors of intraluminal thrombosis indication for frozen elephant trunk should be carefully evaluated and postoperative anticoagulation considered. Early thoracic endovascular aortic repair extension should be considered in patients with intraluminal thrombosis to prevent embolic complications. Stent-graft designs should be improved to prevent intraluminal thrombosis after frozen elephant trunk implantation.

Anticoagulants and reduced thrombus load in abdominal aortic aneurysms assessed with three-dimensional contrast-enhanced ultrasound examination.

OBJECTIVE: The relationship between intraluminal thrombus (ILT) and abdominal aortic aneurysm (AAA) growth and rupture risk remains ambiguous. Studies have shown a limited effect of antiplatelet therapy on ILT size, whereas the impact of anticoagulant therapy on ILT is unresolved. This study aims to evaluate an association between antithrombotic therapy and ILT size assessed with three-dimensional contrast-enhanced ultrasound (3D-CEUS) examination in a cohort of patients with AAA. METHODS: In a cross-sectional study, 309 patients with small AAAs were examined with 3D-CEUS. Patients were divided into three groups based on prescribed antithrombotic therapy: anticoagulant (n = 36), antiplatelet (n = 222), and no antithrombotic therapy (n = 51). Patient ILT size was calculated in volume and thickness and compared between the three groups. RESULTS: Patients on anticoagulants had a significantly lower estimated marginal mean ILT volume of 16 mL (standard error [SE], ±3.2) compared with 28 mL (SE, ±2.7) in the no antithrombotic group and 30 mL (SE, ±1.3) in the antiplatelet group when adjusting for AAA volume (P < .001) and comorbidities (P < .001). In addition, patients on anticoagulant therapy had significantly lower estimated marginal mean ILT thickness of 10 mm (SE, ±1.1) compared with 13 mm (SE, ±0.9) in the no antithrombotic group of and 13mm (SE, ±0.4) in the antiplatelet group when adjusting for AAA diameter (P = .03) and comorbidities (P = .035). CONCLUSIONS: A 3D-CEUS examination is applicable for ILT assessment and demonstrates that patients with AAA on anticoagulant therapy have lower ILT thickness and volume than patients with AAA on antiplatelet therapy and those without antithrombotic therapy. Causality between anticoagulants and ILT size, and extrapolation to AAA growth and rupture risk, is unknown and merits further investigations, to further nuance US-based AAA surveillance strategy.

Towards Precritical Medical Therapy of the Abdominal Aortic Aneurysm.

Pharmacotherapy for abdominal aortic aneurysm (AAA) can be useful for prevention, especially in people at higher risk, for slowing down AAA progression, as well as for post-surgery adjuvant treatment. Our review focuses on novel pharmacotherapy approaches targeted towards slowing down progression of AAA, known also as secondary prevention therapy. Guidelines for AAA are not specific to slow down the expansion rate of an abdominal aortic aneurysm, and therefore no medical therapy is recommended. New ideas are urgently needed to develop a novel medical therapy. We are hopeful that in the future, pharmacologic treatment will play a key role in the prevention and treatment of AAA.