56 research outputs found
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 rĂ©paration endovasculaire des anĂ©vrismes de lâaorte abdominale est limitĂ©e par le dĂ©veloppement des endofuites, qui nĂ©cessite un suivi Ă long terme par imagerie. LâĂ©lastographie sonore de dĂ©formation a Ă©tĂ© proposĂ©e comme mĂ©thode complĂ©mentaire pour aider Ă la dĂ©tection des endofuites et la caractĂ©risation des propriĂ©tĂ©s mĂ©caniques des anĂ©vrismes. On sâintĂ©resse ici Ă©galement Ă la possibilitĂ© de suivre lâembolisation des endofuites, qui est indiquĂ©e dans certains cas mais dont le succĂšs est variable. Un nouvel agent dâembolisation a Ă©tĂ© rĂ©cemment crĂ©Ă© en combinant un hydrogel de chitosane radio-opaque (CH) et le sclĂ©rosant tetradecyl sulfate de sodium (STS), qui sâappelle CH-STS. Le CH-STS dĂ©montre des propriĂ©tĂ©s mĂ©caniques in vitro favorables, mais son comportement in vivo et son effet sur lâĂ©volution du sac par rapport Ă un agent non-sclĂ©rosant pourraient ĂȘtre mieux caractĂ©risĂ©s. Lâobjectif de cette Ă©tude Ă©tait la caractĂ©risation des propriĂ©tĂ©s mĂ©caniques des composantes des endofuites embolisĂ©es avec CH-STS et CH avec Ă©lastographie sonore de dĂ©formation.
MĂ©thodologie : Des anĂ©vrismes bilatĂ©raux avec endofuites de type I ont Ă©tĂ© crĂ©Ă©s au niveau des artĂšres iliaques communes chez neuf chiens. Chez chaque sujet, une endofuite a Ă©tĂ© embolisĂ©e avec CH, et lâautre, avec CH-STS, dâune façon alĂ©atoire et aveugle. Des images dâĂ©chographie duplex et des cinĂ©loops pour Ă©lastographie sonore de dĂ©formation ont Ă©tĂ© acquis Ă 1 semaine, 1 mois, 3 mois et (chez 3 sujets) 6 mois post-embolisation. La tomodensitomĂ©trie a Ă©tĂ© faite Ă 3 mois et (si pertinente) 6 mois post-embolisation. Lâhistopathologie a Ă©tĂ© faite au sacrifice. Les Ă©tudes radiologiques et les donnĂ©es dâhistopathologie ont Ă©tĂ© co-enregistrĂ©es pour dĂ©finir trois rĂ©gions dâintĂ©rĂȘt sur les cinĂ©loops : lâagent dâembolisation (au sacrifice), le thrombus intraluminal (au sacrifice) et le sac anĂ©vrismal (pendant chaque suivi). LâĂ©lastographie sonore de dĂ©formation a Ă©tĂ© faite avec les segmentations par deux observateurs indĂ©pendants. La dĂ©formation axiale maximale (DAM) a Ă©tĂ© le critĂšre dâĂ©valuation principal. Les analyses statistiques ont Ă©tĂ© faites avec des modĂšles mixtes linĂ©aires gĂ©nĂ©ralisĂ©s et des coefficients de corrĂ©lations intraclasses (ICCs).
RĂ©sultats : Des endofuites rĂ©siduelles ont Ă©tĂ© trouvĂ©es dans 7/9 (77.8%) et 4/9 (44.4%) des anĂ©vrismes embolisĂ©s 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 Ă©levĂ©e (p = 0.079) que le CH-STS. Il nây avait aucune diffĂ©rence entre les thrombi associĂ©s avec les deux traitements. Les sacs anĂ©vrismaux embolisĂ©s avec CH-STS ont eu une DAM 29% plus basse (p < 0.001) que ceux embolisĂ©s avec CH. Des endofuites rĂ©siduelles ont Ă©tĂ© associĂ©es avec une DAM du sac anĂ©vrismal 53% plus Ă©levĂ©e (p < 0.001). Le ICC pour la DAM a Ă©tĂ© de 0.807 entre les deux segmentations.
Conclusion : Le CH-STS confĂšre des valeurs de dĂ©formations plus basses aux anĂ©vrismes embolisĂ©s. Les endofuites persistantes sont associĂ©es avec des dĂ©formations plus Ă©levĂ©es du sac anĂ©vrismal.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-STSâcontaining a chitosan hydrogel and the sclerosant sodium tetradecyl sulphate (STS)âwas 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-STSâincluding the agent, the intraluminal thrombus (ILT), and the overall sacâvia 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, andâin 3 subjectsâ6 months post-embolization. Contrast-enhanced CT was performed at 3 months andâwhere applicableâ6 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 readersâ 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
Analysis of Blood Flow in Patient-specific Models of Type B Aortic Dissection
Aortic dissection is the most common acute catastrophic event affecting the aorta. The
majority of patients presenting with an uncomplicated type B dissection are treated
medically, but 25% of these patients develop subsequent dilatation and aortic aneurysm
formation. The reasons behind the longâterm outcomes of type B aortic dissection are
poorly understood. As haemodynamic factors have been involved in the development
and progression of a variety of cardiovascular diseases, the flow phenomena and
environment in patientâspecific models of type B aortic dissection have been studied in
this thesis by applying computational fluid dynamics (CFD) to in vivo data. The present
study aims to gain more detailed knowledge of the links between morphology, flow
characteristics and clinical outcomes in type B dissection patients.
The thesis includes two parts of patientâspecific study: a multiple case crossâsectional
study and a single case longitudinal study. The multiple cases study involved a group of
ten patients with classic type B aortic dissection with a focus on examining the flow
characteristics as well as the role of morphological factors in determining the flow
patterns and haemodynamic parameters. The single case study was based on a series of
followâup scans of a patient who has a stable dissection, with an aim to identify the
specified haemodynamic factors that are associated with the progression of aortic
dissection. Both studies were carried out based on computed tomography images
acquired from the patients. 4D Phaseâcontrast magnetic resonance imaging was
performed on a typical type B aortic dissection patient to provide detailed flow data for
validation purpose. This was achieved by qualitative and quantitative comparisons of
velocityâencoded images with simulation results of the CFD model.
The analysis of simulation results, including velocity, wall shear stress and turbulence
intensity profiles, demonstrates certain correlations between the morphological
features and haemodynamic factors, and also their effects on longâterm outcomes of
type B aortic dissections. The simulation results were in good agreement with in vivo
MR flow data in the patientâspecific validation case, giving credence to the application of
the computational model to the study of flow conditions in aortic dissection. This study
made an important contribution by identifying the role of certain morphological and
haemodynamic factors in the development of type B aortic dissection, which may help
provide a better guideline to assist surgeons in choosing optimal treatment protocol for
individual patient
Scanning protocol optimisation for dual-energy computed tomography angiography in peripheral artery stenting
In this thesis, a novel approach has been proposed to evaluate the optimal scanning protocol for dual energy computed tomography angiography in peripheral arterial stents. This new approach includes evaluation of different protocols and image reconstructions at different energy level, development of the optimal protocol based on lowest radiation dose and acceptable image quality. Furthermore, an optimal contrast medium protocol has been identified in imaging peripheral arterial disease
Design of a testing device for an anatomical part of the ascending aorta
Aortic aneurysms are life-threatening pathologies that cause thousands of deaths worldwide.
The current main clinical criteria for surgical intervention is aortic diameter, although a large
percentage of patients with dissection or rupture has a normal diameter. Computation methods
have been adopted to model the biomechanical behaviour of biological tissue in view of adding in
the diagnosis of this pathology. Furthermore, experimental testing on aneurismatic aortic tissue
has been performed to validate these models. The objective of this study is to integrate com-
putational mechanical methods into an innovative experimental test with a specifically designed
device where material parameters are obtained by inverse methods assisted by Digital Image
Correlation (DIC). Axiomatic Design (AD) is taken into consideration to develop the testing
device in a clear, methodical, and efficient way. A case study is analysed, and a patient-specific
3D geometry of an Ascending Thoracic Aortic Aneurysm (ATAA) is obtained by segmenting
Computed Tomography Angiography (CTA) images. A methodology is presented by attribut-
ing a hyperelastic constitutive model to the geometry and executing Finite Element Analysis
(FEA). Future work should rely on real experimental tests where Finite Element Model Up-
dating (FEMU) should be adopted to fit the constitutive model more accurately to the actual
specimen material.O aneurisma da aorta Ă© uma patologia de risco que provoca milhares de mortes mundialmente.
O critĂ©rio atual para intervenção cirĂșrgica Ă© o diĂąmetro da aorta, no entanto, uma grande
percentagem de pacientes com dissecção ou rutura da aorta apresenta um diùmetro normal.
MĂ©todos computacionais tĂȘm sido adotados para modelar o comportamento biomecĂąnico de
tecido biolĂłgico e auxiliar no diagnĂłstico desta patologia. Testes experimentais nestes tecidos
sĂŁo executados para validar os modelos. O objetivo deste estudo Ă© um contributo para uma
plataforma digital integrando métodos computacionais para o desenvolvimento de um mecan-
ismo de ensaio experimental, cuja identificação de parùmetros material deve ser auxiliada pela
técnica de correlação digital de imagem 3D. Esta abordagem segue um desenvolvimento de pro-
duto orientado por simulação numérica, em que a anålise computacional é totalmente integrada
como parte do projeto mecùnico. Teoria Axiomåtica de Projeto é tida em consideração para
desenvolver o dispositivo de uma forma clara, metĂłdica e eficiente. Um caso de estudo Ă© anal-
isado e uma geometria da peça anatĂłmica 3D, especĂfica de um paciente, Ă© obtida atravĂ©s da
segmentação de imagens de uma angiotomografia. Uma metodologia é apresentada atribuindo
um modelo constitutivo hiperelĂĄstico ao material e executando anĂĄlise de elementos finitos.
Como trabalho futuro a identificação dos parametros constitutivos deve ser obtida com recurso
a métodos inversos avançados baseados em campos de deformação obtidos por correlação digital
de imagem
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