In recent years, Transcatheter Aortic Valve Implantation (TAVI) has become the standard medical treatment for patients with aortic stenosis who cannot undergo conventional surgery. There are several factors that can affect the correct placement of the implant during surgery, the most significant being the presence of calcifications. These prevent the stent from adhering properly to the aortic wall, causing a regurgitation problem called paravalvular leakage (PVL). Therefore, computational simulations represent a valuable approach to provide the physician with an additional tool for evaluating the operation and predicting these post-operative complications in advance. The present thesis deals with post-TAVI fluid dynamic simulations with special focus on the generation of volume meshes for the fluid domain. Alternative tools have been tested. In particular three methods are compared: one based on the campus-licensed Matlab software, one based on the open-source ParaView software and one based on a powerful but very expensive commercial software. In this thesis, the ways of Matlab and ParaView were investigated. The results are then compared with those of the commercial software that allows a very detailed analysis of the problem. To perform the fluid dynamic analysis, we used ANSYS Fluent. It was further necessary to implement a Matlab code that could provide the required information to write the volume mesh in a format compatible with the software. We have observed from the results that a smaller mesh size allows a better resolution of the NS equations and consequently it allows to perform a CFD simulation more faithful to the real clinical situation. Despite the long computational times and the less accurate results, the described procedures could be useful for an inspection analysis of the problem before resorting to a more accurate simulation with a more powerful yet also more expensive software.
Negli ultimi anni, l'impianto della valvola aortica transcatetere (TAVI) è diventato il trattamento medico standard per i pazienti con stenosi aortica che non possono sottoporsi alla chirurgia convenzionale. Ci sono diversi fattori che possono influenzare il corretto posizionamento dell'impianto durante l'intervento, il più significativo dei quali è la presenza di calcificazioni. Queste impediscono allo stent di aderire correttamente alla parete aortica, causando un problema di rigurgito chiamato perdita paravalvolare (PVL). Pertanto, le simulazioni computazionali rappresentano un valido approccio per fornire al medico un ulteriore strumento per valutare l'operazione e prevedere in anticipo queste complicazioni post-operatorie. La presente tesi si occupa di simulazioni fluidodinamiche post-TAVI con particolare attenzione alla generazione di mesh di volume per il dominio del fluido. Sono stati testati strumenti alternativi. In particolare, sono stati confrontati tre metodi: uno basato sul software Matlab con una licenza disponibile in campus, uno basato sul software open-source ParaView e uno basato su un software commerciale potente ma molto costoso. In questa tesi, sono state studiate le procedure di Matlab e ParaView. I risultati sono poi confrontati con quelli del software commerciale che permette un'analisi molto dettagliata del problema. Per eseguire l'analisi fluidodinamica, abbiamo utilizzato ANSYS Fluent. È stato inoltre necessario implementare un codice Matlab che potesse fornire le informazioni necessarie per scrivere la mesh di volume in un formato compatibile con il software. Abbiamo osservato dai risultati che una mesh di dimensione minore permette una migliore risoluzione delle equazioni di NS e di conseguenza di ottenere una simulazione CFD più fedele alla situazione clinica reale esaminata. Nonostante i lunghi tempi di calcolo e i risultati meno accurati, le procedure descritte potrebbero essere utili per un'analisi di controllo del problema prima di ricorrere a una simulazione più accurata con un software più potente ma anche molto costoso.
Impact of volume mesh generation in the accuracy of post-interventional TAVI simulations results
D'APRILE, DONATO
2019/2020
Abstract
In recent years, Transcatheter Aortic Valve Implantation (TAVI) has become the standard medical treatment for patients with aortic stenosis who cannot undergo conventional surgery. There are several factors that can affect the correct placement of the implant during surgery, the most significant being the presence of calcifications. These prevent the stent from adhering properly to the aortic wall, causing a regurgitation problem called paravalvular leakage (PVL). Therefore, computational simulations represent a valuable approach to provide the physician with an additional tool for evaluating the operation and predicting these post-operative complications in advance. The present thesis deals with post-TAVI fluid dynamic simulations with special focus on the generation of volume meshes for the fluid domain. Alternative tools have been tested. In particular three methods are compared: one based on the campus-licensed Matlab software, one based on the open-source ParaView software and one based on a powerful but very expensive commercial software. In this thesis, the ways of Matlab and ParaView were investigated. The results are then compared with those of the commercial software that allows a very detailed analysis of the problem. To perform the fluid dynamic analysis, we used ANSYS Fluent. It was further necessary to implement a Matlab code that could provide the required information to write the volume mesh in a format compatible with the software. We have observed from the results that a smaller mesh size allows a better resolution of the NS equations and consequently it allows to perform a CFD simulation more faithful to the real clinical situation. Despite the long computational times and the less accurate results, the described procedures could be useful for an inspection analysis of the problem before resorting to a more accurate simulation with a more powerful yet also more expensive software.È consentito all'utente scaricare e condividere i documenti disponibili a testo pieno in UNITESI UNIPV nel rispetto della licenza Creative Commons del tipo CC BY NC ND.
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https://hdl.handle.net/20.500.14239/12662