The Thoracic Endovascular Aortic Repair (TEVAR) is a minimally invasive procedure used to treat aortic dissections, which consist in the tearing of the innermost aortic walls layer, and the development of an intimal flap and two lumens. This mini-invasive procedure consists in inserting a stent-graft through the true lumen and deploying it to push the flap against the aortic wall, restoring the physiological blood flow. Although TEVAR has advantages over open surgery, it can lead to post-implant complications. For this reason, computational modelling represents a valuable tool to help clinicians in the pre-planning procedure. The present thesis aims to reproduce TEVAR on two patient-specific aortic dissection models. Patient A presented tetrahedral layers on the aortic walls, and the intimal flap was discretized with a tetrahedral mesh. Four different material formulations were chosen for the aorta, three hyperelastic isotropic (2nd Order Polynomial, 2nd Order Ogden, Mooney-Rivlin five parameters) and one linear elastic, while the intimal flap was modelled as linear elastic. On patient B, instead, the aorta was meshed with triangular shell elements, imposing a linear elastic material. Then, its intimal flap was modelled as in the previous case, but with a Young’s modulus that varied from 0.3 to 1 MPa. The analysis on the first patient aimed at understanding the most suitable parameters for the aortic walls. The four material formulations and the tetrahedral and the shell mesh were compared, and the stress and strain results showed no marked differences in both cases. Concerning patient B, interesting results were observed on the intimal flap, with a decreasing trend for the stresses and contact pressures, and an increasing one for the strains as the stiffness of the flap decreased. In conclusion, modelling the aorta as a linear elastic material with shell elements was proved to be acceptable. Furthermore, a decrease in flap compliance resulted in a reduction in von Mises stress, as expected. This analysis allowed to comprehend that the simulations of the TEVAR procedure in patient-specific anatomies with dissection has been successfully replicated in-silico.
La Riparazione Endovascolare dell’Aorta Toracica (TEVAR) è una procedura chirurgica mininvasiva per il trattamento delle dissezioni aortiche, lacerazioni dello strato più interno della parete aortica che causano lo sviluppo di un flap intimale e di due lumi. Tale procedura consiste nell’impianto di uno stent-graft di modo tale da spingere il flap contro la parete aortica e ristabilire il fisiologico flusso sanguigno. Nonostante la procedura TEVAR offra dei vantaggi rispetto alla chirurgia a cielo aperto, essa non è esente da complicazioni. È in questo campo che si inseriscono gli studi in-silico, che permettono di assistere il chirurgo nella fase pre-operatoria. Questo lavoro di tesi ha lo scopo di riprodurre la procedura TEVAR in due anatomie paziente-specifico con dissezioni. Per il paziente A si è utilizzata una mesh tetraedrica sia per l’aorta che per il flap intimale. Per le pareti aortiche sono state scelte tre formulazioni isotropiche iperelastiche (2nd Order Polynomial, 2nd Order Ogden, Mooney-Rivlin five parameters) e una lineare elastica, mentre il flap intimale è stato modellizzato lineare elastico. Nel paziente B l’aorta è stata modellizzata come shell triangolare e materiale lineare elastico, mentre il flap è stato modellizzato come nel caso precedente, ma variando il suo modulo di Young nell’intervallo 0.3–1 MPa. L’analisi sul primo paziente ha permesso di scegliere i parametri più adatti per modellizzare il vaso. Comparando le quattro formulazioni di materiali e la mesh tetraedrica con quella a shell non si sono trovate differenze significative in termini di sforzi e deformazioni. Nel caso del paziente B, invece, risultati interessanti sono stati riscontrati sul flap intimale, con un andamento decrescente per gli stress e le pressioni di contatto, e uno crescente per le deformazioni al decrescere della rigidezza del flap. In conclusione, la modellizzazione dell’aorta con un materiale lineare elastico ed elementi shell è stata ritenuta accettabile. Inoltre, la diminuzione della compliance del flap ha portato a una riduzione degli stress. L’analisi ha dimostrato la fattibilità di riprodurre, in-silico, la procedura TEVAR in aorte con dissezione.
A computational study on aortic dissections in patient-specific TEVAR procedures
LIMONTA, EMMA;Mariani, Eleonora
2023/2024
Abstract
The Thoracic Endovascular Aortic Repair (TEVAR) is a minimally invasive procedure used to treat aortic dissections, which consist in the tearing of the innermost aortic walls layer, and the development of an intimal flap and two lumens. This mini-invasive procedure consists in inserting a stent-graft through the true lumen and deploying it to push the flap against the aortic wall, restoring the physiological blood flow. Although TEVAR has advantages over open surgery, it can lead to post-implant complications. For this reason, computational modelling represents a valuable tool to help clinicians in the pre-planning procedure. The present thesis aims to reproduce TEVAR on two patient-specific aortic dissection models. Patient A presented tetrahedral layers on the aortic walls, and the intimal flap was discretized with a tetrahedral mesh. Four different material formulations were chosen for the aorta, three hyperelastic isotropic (2nd Order Polynomial, 2nd Order Ogden, Mooney-Rivlin five parameters) and one linear elastic, while the intimal flap was modelled as linear elastic. On patient B, instead, the aorta was meshed with triangular shell elements, imposing a linear elastic material. Then, its intimal flap was modelled as in the previous case, but with a Young’s modulus that varied from 0.3 to 1 MPa. The analysis on the first patient aimed at understanding the most suitable parameters for the aortic walls. The four material formulations and the tetrahedral and the shell mesh were compared, and the stress and strain results showed no marked differences in both cases. Concerning patient B, interesting results were observed on the intimal flap, with a decreasing trend for the stresses and contact pressures, and an increasing one for the strains as the stiffness of the flap decreased. In conclusion, modelling the aorta as a linear elastic material with shell elements was proved to be acceptable. Furthermore, a decrease in flap compliance resulted in a reduction in von Mises stress, as expected. This analysis allowed to comprehend that the simulations of the TEVAR procedure in patient-specific anatomies with dissection has been successfully replicated in-silico.File | Dimensione | Formato | |
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2025_04_Limonta_Mariani_Executive Summary.pdf
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2025_04_Limonta_Mariani_Tesi.pdf
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https://hdl.handle.net/10589/235906