Abdominal aortic aneurysm: Treatment options, image visualizations and follow-up procedures

Abdominal aortic aneurysm is a common vascular disease that affects elderly population. Open surgical repair is regarded as the gold standard technique for treatment of abdominal aortic aneurysm, however, endovascular aneurysm repair has rapidly expanded since its first introduction in 1990s. As a less invasive technique, endovascular aneurysm repair has been confirmed to be an effective alternative to open surgical repair, especially in patients with co-morbid conditions. Computed tomography (CT) angiography is currently the preferred imaging modality for both preoperative planning and post-operative follow-up. 2D CT images are complemented by a number of 3D reconstructions which enhance the diagnostic applications of CT angiography in both planning and follow-up of endovascular repair. CT has the disadvantage of high cummulative radiation dose, of particular concern in younger patients, since patients require regular imaging follow-ups after endovascular repair, thus, exposing patients to repeated radiation exposure for life. There is a trend to change from CT to ultrasound surveillance of endovascular aneurysm repair. Medical image visualizations demonstrate excellent morphological assessment of aneurysm and stent-grafts, but fail to provide hemodynamic changes caused by the complex stent-graft device that is implanted into the aorta. This article reviews the treatment options of abdominal aortic aneurysm, various image visualization tools, and follow-up procedures with use of different modalities including both imaging and computational fluid dynamics methods. Future directions to improve treatment outcomes in the follow-up of endovascular aneurysm repair are outlined

Planning and Sizing with OsiriX/Horos

It is known that endovascular aneurysm repair (EVAR) requires a precise deployment of the graft and so the anatomical and morphological characteristic study of the aorta and its branches is mandatory. The increase of endovascular surgeons’ interest on tomography image edition through software is marked specially when the increasing frequency of these procedures and its complexity have impelled surgeons to face additional and successive risk to occupational radiation exposure. Thus, a meticulous study of the angio-CT during EVAR preparation allows the reduction of unnecessary radiation exposure, as it also reduces consecutive image acquisition and contrast use (that may be related to renal overload in susceptible patients). Although some studies propose effective strategies to optimize the procedure, they rely on the use of additional specific and advanced equipment, available only in major centers. As an alternative, a simpler technique through image manipulation on the software OsiriX/Horos, aiming to reduce both exposures, is presented

Determination of Stent Frame Displacement After Endovascular Aneurysm Sealing

Purpose: To describe and validate a new methodology for visualizing and quantifying 3-dimensional (3D) displacement of the stent frames of the Nellix endosystem after endovascular aneurysm sealing (EVAS). Methods: The 3D positions of the stent frames were registered to 5 fixed anatomical landmarks on the post-EVAS computed tomography (CT) scans, facilitating comparison of the position and shape of the stent frames between consecutive follow-up scans. Displacement of the proximal and distal ends of the stent frames, the entire stent frame trajectories, as well as changes in distance between the stent frames were determined for 6 patients with >5-mm displacement and 6 patients with 5-mm displacement on the 1-year CT as determined by the new methodology, 2 went on to develop a type Ia endoleak in longer follow-up, and displacement progressed to >15 mm for 2 other patients. No endoleak or progressive displacement was appreciated for the patients with 5 mm on the 1-year CT scans reconstructed with the new methodology may forecast impaired sealing and anchoring of the Nellix endosystem

Prediction of guidewire-induced aortic deformations during EVAR: a finite element and in vitro study

Introduction and aims: During an Endovascular Aneurysm Repair (EVAR) procedure a stiff guidewire is inserted from the iliac arteries. This induces significant deformations on the vasculature, thus, affecting the pre-operative planning, and the accuracy of image fusion. The aim of the present work is to predict the guidewire induced deformations using a finite element approach validated through experiments with patient-specific additive manufactured models. The numerical approach herein developed could improve the pre-operative planning and the intra-operative navigation. Material and methods: The physical models used for the experiments in the hybrid operating room, were manufactured from the segmentations of pre-operative Computed Tomography (CT) angiographies. The finite element analyses (FEA) were performed with LS-DYNA Explicit. The material properties used in finite element analyses were obtained by uniaxial tensile tests. The experimental deformed configurations of the aorta were compared to those obtained from FEA. Three models, obtained from Computed Tomography acquisitions, were investigated in the present work: A) without intraluminal thrombus (ILT), B) with ILT, C) with ILT and calcifications. Results and discussion: A good agreement was found between the experimental and the computational studies. The average error between the final in vitro vs. in silico aortic configurations, i.e., when the guidewire is fully inserted, are equal to 1.17, 1.22 and 1.40 mm, respectively, for Models A, B and C. The increasing trend in values of deformations from Model A to Model C was noticed both experimentally and numerically. The presented validated computational approach in combination with a tracking technology of the endovascular devices may be used to obtain the intra-operative configuration of the vessels and devices prior to the procedure, thus limiting the radiation exposure and the contrast agent dose.publishedVersio

Correlation Between Intrasac Pressure Measurements of a Pressure Sensor and an Angiographic Catheter During Endovascular Repair of Abdominal Aortic Aneurysm

PURPOSE: To establish a correlation between intrasac pressure measurements of a pressure sensor and an angiographic catheter placed in the same aneurysm sac before and after its exclusion by an endoprosthesis. METHODS: Patients who underwent endovascular abdominal aortic aneurysm repair and received an EndoSureTM wireless pressure sensor implant between March 19 and December 11, 2004 were enrolled in the study. Simultaneous readings of systolic, diastolic, mean, and pulse pressure within the aneurysm sac were obtained from the catheter and the sensor, both before and after sac exclusion by the endoprosthesis (Readings 1 and 2, respectively). Intrasac pressure measurements were compared using Pearson's correlation and Student's t test. Statistical significance was set at p<0.05. RESULTS: Twenty-five patients had the pressure sensor implanted, with simultaneous readings (i.e., recorded by both devices) obtained in 19 patients for Reading 1 and in 10 patients for Reading 2. There was a statistically significant correlation for all pressure variables during both readings, with p<0.01 for all except the pulse pressure in Reading 1 (p<0.05). Statistical significance of pressure variations before and after abdominal aortic aneurysm exclusion was coincident between the sensor and catheter for diastolic (p>0.05), mean (p>0.05), and pulse (p<0.01) pressures; the sole disagreement was observed for systolic pressure, which varied, on average, 31.23 mmHg by the catheter (p<0.05) and 22 mmHg (p>0.05) by the sensor. CONCLUSION: The excellent agreement between intrasac pressure readings recorded by the catheter and the sensor justifies use of the latter for detection of post-exclusion abdominal aortic aneurysm pressurization

Helical CT angiography of fenestrated stent grafting of abdominal aortic aneurysms

Fenestrated stent grafts have been developed to treat patients with abdominal aortic aneurysms (AAA) associated with complicated aneurysm necks, such as short necks, severe angulated or poor quality necks (presence of calcification or thrombus). The technique is performed by creating an opening in the graft material so that the stent graft can be placed above the renal and other visceral branches without compromising blood perfusion to these vessels. In most situations, a supporting stent is inserted into the fenestrated vessel to provide fixation of the fenestrated vessel against stent grafts, as well as to preserve patency of the vessel. Helical CT angiography (CTA) is the preferred imaging modality in both pre-operative planning and post-procedural follow-up of fenestrated repair of AAA. The main concerns of fenestrated stent grafting lie in the following two aspects: patency of the fenestrated vessels and position of the fenestrated stents in relation to the artery branches. In this article, the author presents the clinical applications of 2D and 3D visualizations in the follow-up of patients with AAA treated with fenestrated stent grafts, with the aim of providing useful information to readers and increasing their knowledge of an increasingly used technique, fenestrated stent grafting in the treatment of AAA

Numerical Insights for AAA Growth Understanding and Predicting: Morphological and Hemodynamic Risk Assessment Features and Transient Coherent Structures Uncovering

Les anévrismes de l'aorte abdominale (AAA) sont des dilatations localisées et fréquentes de l'aorte. En cas de rupture, seul un traitement immédiat peut prévenir la morbidité et la mortalité. Le diamètre maximal AAA ($D_{max}$) et la croissance sont les paramètres actuels pour évaluer le risque associé et planifier l'intervention, avec des seuils inférieurs pour les femmes. Cependant, ces critères ne sont pas personnalisés ; la rupture peut se produire à un diamètre inférieur et les patients vivre avec un AAA important. Si l'on sait que la maladie est associée à une modification de la morphologie et de la circulation sanguine, à un dépôt de thrombus intra-luminal et à des symptômes cliniques, les mécanismes de croissance ne sont pas encore entièrement compris. Dans cette étude longitudinale, une analyse morphologique et des simulations de flux sanguins sont effectuées et comparées aux sujets témoins chez 32 patients ayant reçu un diagnostic clinique d'AAA et au moins 3 tomodensitogrammes de suivi par patient. L'objectif est d'abord d'examiner quels paramètres stratifient les patients entre les groupes sains, à faible risque et à risque élevé. Les corrélations locales entre les paramètres hémodynamiques et la croissance de l'AAA sont également explorées, car la croissance hétérogène de l'AAA n'est actuellement pas comprise. Enfin, les paramètres composites sont construits à partir de données cliniques, morphologiques et hémodynamiques et de leur capacité à prédire si un patient sera soumis à un test de risque. La performance de ces modèles construits à partir de l'apprentissage supervisé est évaluée par les ROC AUC : ils sont respectivement de 0.73 ± 0.09, 0.93 ± 0.08 et 0.96 ± 0.10 . En incorporant tous les paramètres, on obtient une AUC de 0.98 ± 0.06. Pour mieux comprendre les interactions entre la croissance et la topologie de l'écoulement de l'AAA, on propose un worflow spécifique au patient pour calculer les exposants de Lyapunov en temps fini et extraire les structures lagrangiennes-cohérentes (SLC). Ce modèle de calcul a d'abord été comparé à l'imagerie par résonance magnétique (IRM) par contraste de phase 4-D chez 5 patients. Pour mieux comprendre l'impact de la topologie de l'écoulement et du transport sur la croissance de l'AAA, des SLC hyperboliques répulsives ont été calculées chez un patient au cours d'un suivi de 8 ans, avec 9 mesures morphologiques volumétriques de l'AAA par tomographie-angiographie. Les SLC ont défini les frontières du jet entrant dans l'AAA. Les domaines situés entre le SLC et le mur aortique ont été considérés comme des zones de stagnation. Leur évolution a été étudiée lors de la croissance de l'AAA. En plus des SLC hyperboliques (variétés attractives et répulsives) découvertes par FTLE, les SLC elliptiques ont également été considérées. Il s'agit de régions dominées par la rotation, ou tourbillons, qui sont de puissants outils pour comprendre les phénomènes de transport dans les AAA.Abdominal aortic aneurysms (AAA) are localized, commonly-occurring dilations of the aorta. In the event of rupture only immediate treatment can prevent morbidity and mortality. The AAA maximal diameter ($D_{max}$) and growth are the current metrics to evaluate the associated risk and plan intervention, with lower thresholds for women. However, these criteria lack patient specificity; rupture may occur at lower diameter and patients may live with large AAA. If the disease is known to be associated with altered morphology and blood flow, intra-luminal thrombus deposit and clinical symptoms, the growth mechanisms are yet to be fully understood. In this longitudinal study, morphological analysis and blood flow simulations for 32 patients with clinically diagnosed AAA and at least 3 follow-up CT-scans per patient, are performed and compared to control subjects. The aim is first to investigate which metrics stratify patients between healthy, low risk and high risk groups. Local correlations between hemodynamical metrics and AAA growth are also explored, as AAA heterogeneous growth is currently not understood. Finally, composite metrics are built from clinical, morphological, and hemodynamical data, and their ability to predict if a patient will become at risk tested. Performance of these models built from supervised learning is assessed by ROC AUCs: they are respectively, 0.73 ± 0.09, 0.93 ± 0.08 and 0.96 ± 0.10. Mixing all metrics, an AUC of 0.98 ± 0.06 is obtained. For further insights into AAA flow topology/growth interaction, a workout of patient-specific computational flow dynamics (CFD) is proposed to compute finite-time Lyapunov exponents and extract Lagrangian-coherent structures (LCS). This computational model was first compared with 4-D phase-contrast magnetic resonance imaging (MRI) on 5 patients. To better understand the impact of flow topology and transport on AAA growth, hyperbolic, repelling LCS were computed in 1 patient during 8-years follow-up, including 9 volumetric morphologic AAA measures by computed tomography-angiography (CTA). LCS defined barriers to Lagrangian jet cores entering AAA. Domains enclosed between LCS and the aortic wall were considered to be stagnation zones. Their evolution was studied during AAA growth. In addition to hyperbolic (attracting and repelling) LCS uncovered by FTLE, elliptic LCS were also considered. Those encloses rotation-dominated regions, or vortices, which are powerful tools to understand the flow transport in AAA

Strain ultrasound elastography of aneurysm sac content after randomized endoleak embolization with sclerosing and non-sclerosing chitosan-based hydrogels in a preclinical model

Mise en contexte : La réparation endovasculaire des anévrismes de l’aorte abdominale est limitée par le développement des endofuites, qui nécessite un suivi à long terme par imagerie. L’élastographie sonore de déformation a été proposée comme méthode complémentaire pour aider à la détection des endofuites et la caractérisation des propriétés mécaniques des anévrismes. On s’intéresse ici également à la possibilité de suivre l’embolisation des endofuites, qui est indiquée dans certains cas mais dont le succès est variable. Un nouvel agent d’embolisation a été récemment créé en combinant un hydrogel de chitosane radio-opaque (CH) et le sclérosant tetradecyl sulfate de sodium (STS), qui s’appelle CH-STS. Le CH-STS démontre des propriétés mécaniques in vitro favorables, mais son comportement in vivo et son effet sur l’évolution du sac par rapport à un agent non-sclérosant pourraient être mieux caractérisés. L’objectif de cette étude était la caractérisation des propriétés mécaniques des composantes des endofuites embolisées avec CH-STS et CH avec élastographie sonore de déformation. Méthodologie : Des anévrismes bilatéraux avec endofuites de type I ont été créés au niveau des artères iliaques communes chez neuf chiens. Chez chaque sujet, une endofuite a été embolisée avec CH, et l’autre, avec CH-STS, d’une façon aléatoire et aveugle. Des images d’échographie duplex et des cinéloops pour élastographie sonore de déformation ont été acquis à 1 semaine, 1 mois, 3 mois et (chez 3 sujets) 6 mois post-embolisation. La tomodensitométrie a été faite à 3 mois et (si pertinente) 6 mois post-embolisation. L’histopathologie a été faite au sacrifice. Les études radiologiques et les données d’histopathologie ont été co-enregistrées pour définir trois régions d’intérêt sur les cinéloops : l’agent d’embolisation (au sacrifice), le thrombus intraluminal (au sacrifice) et le sac anévrismal (pendant chaque suivi). L’élastographie sonore de déformation a été faite avec les segmentations par deux observateurs indépendants. La déformation axiale maximale (DAM) a été le critère d’évaluation principal. Les analyses statistiques ont été faites avec des modèles mixtes linéaires généralisés et des coefficients de corrélations intraclasses (ICCs). Résultats : Des endofuites résiduelles ont été trouvées dans 7/9 (77.8%) et 4/9 (44.4%) des anévrismes embolisés avec CH et CH-STS, respectivement. Le CH-STS a eu une DAM 66 % plus basse (p < 0.001) que le CH. Le thrombus a eu une DAM 37% plus basse (p = 0.010) que le CH et 77% plus élevée (p = 0.079) que le CH-STS. Il n’y avait aucune différence entre les thrombi associés avec les deux traitements. Les sacs anévrismaux embolisés avec CH-STS ont eu une DAM 29% plus basse (p < 0.001) que ceux embolisés avec CH. Des endofuites résiduelles ont été associées avec une DAM du sac anévrismal 53% plus élevée (p < 0.001). Le ICC pour la DAM a été de 0.807 entre les deux segmentations. Conclusion : Le CH-STS confère des valeurs de déformations plus basses aux anévrismes embolisés. Les endofuites persistantes sont associées avec des déformations plus élevées du sac anévrismal.Background: Endovascular aneurysm repair (EVAR) is the modality of choice for the treatment of abdominal aortic aneurysms (AAAs). EVAR is limited by the development of endoleaks, which necessitate long-term imaging follow-up. Conventional follow-up modalities suffer from unique limitations. Strain ultrasound elastography (SUE) has been recently proposed as an imaging adjunct to detect endoleaks and to characterize aneurysm mechanical properties. Once detected, certain endoleaks may be treated with embolization; however, success is limited. In this context, the embolic agent CH-STS—containing a chitosan hydrogel and the sclerosant sodium tetradecyl sulphate (STS)—was created. CH-STS demonstrates favorable mechanical properties in vitro; however, its behavior in vivo and impact on sac evolution compared to a non-sclerosing chitosan-based embolic agent (CH) merit further characterization. Purpose: To compare the mechanical properties of the constituents of endoleaks embolized with CH and CH-STS—including the agent, the intraluminal thrombus (ILT), and the overall sac—via SUE. Methods: Bilateral common iliac artery aneurysms with type I endoleaks were created in nine dogs. In each animal, one endoleak was randomly embolized with CH, and the other with CH-STS. Duplex ultrasound (DUS) and radiofrequency cine loops were acquired at 1 week, 1 month, 3 months, and—in 3 subjects—6 months post-embolization. Contrast-enhanced CT was performed at 3 months and—where applicable—6 months post-embolization. Histopathological analysis was performed at time of sacrifice. Radiological studies and histopathological slides were co-registered to identify three regions of interest (ROIs) on the cine loops: embolic agent (at sacrifice), ILT (at sacrifice), and aneurysm sac (at all follow-up times). SUE was performed using segmentations from two independent observers on the cine loops. Maximum axial deformation (MAD) was the main outcome. Statistical analysis was performed using general linear mixed models and intraclass correlation coefficients (ICCs). Results: Residual endoleaks were identified in 7/9 (77.8%) and 4/9 (44.4%) aneurysms embolized with CH and CH-STS, respectively. CH-STS had a 66 % lower MAD (p < 0.001) than CH. The ILT had a 37% lower MAD (p = 0.010) than CH and a 77% greater MAD (p = 0.079; trending towards significance) than CH-STS. There was no difference in the ILT between treatment groups. Aneurysm sacs embolized with CH-STS had a 29% lower MAD (p < 0.001) than those with CH. Residual endoleak increased MAD of the aneurysm sac by 53% (p < 0.001), regardless of the agent used. The ICC for MAD was 0.807 between readers’ segmentations. Conclusion: CH-STS confers lower strain values to embolized aneurysms. Persistent endoleaks result are associated with increased sac strain, which may be useful for clinical follow-up

Use of nanoparticles as contrast agents for the functional and molecular imaging of abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is a degenerative disease of the aorta common in adults older than 65 years of age. AAA is usually imaged using ultrasound or computed tomography. Molecular imaging technologies employing nanoparticles have been proposed as novel ways to quantify pathological processes, such as inflammation, within AAAs as a means to identify the risk of rapid progression or rupture. This article reviews the current evidence supporting the role of nanoparticle-based imaging in the management of AAA. Currently, ultrasmall superparamagnetic nanoparticles enhanced magnetic resonance imaging appears to hold the greatest potential for imaging macrophage-mediated inflammation in human AAA