A preclinical haemodynamic evaluation of a pulmonary prosthetic valve’s performance requires hydraulic circuit, i.e. mock loops, which reproduce in vitro the human pulmonary circulation. To achieve, by using a unique set-up, macroscopic fluid dynamic measurements (e.g. pressure and flow rate) and local haemodynamic parameters, mock loops could be adopted with imaging techniques, such as 4D-flow achieved through magnetic resonance (MRI). Conventional mock loop, since they in general include ferromagnetic materials, have to undergo to an adaptation process to the MRI magnetic environment. The MRI-compatible mock loop proposed in this work consists in placing a pulsatile piston pump, realized with ferromagnetic materials, outside the MRI room and connected with the circuit with long silicon tubes. A literature analysis shows that no adjustable pulmonary impedance simulator that features a linear resistance are available yet. Hence, a dimensioning and designing process is conducted in this work. For each component of the proposed modular structure, encumbrance and non-ferromagnetic materials are supplied, to provide the basis for the manufacturing process of the MRI-compatible adjustable pulmonary impedance simulator. Specifically, the regulator system is characterized by hydraulic experimental tests, which allow to identify its range of functioning. The behaviour of the mock loop, that includes the proposed pumping system and the dimensioned and designed afterload, is evaluated by using a lumped parameter approach. The simulations show that the proposed system is able to reproduce at the pulmonary valve level the pulmonary pressure and flow waveforms either in pathological or physiological conditions by accounting for different working medium viscosity. The modular structure proposed for the mock loop allows to replace one of its components to adjust their influence on the reproduced pulmonary waveforms.
La valutazione preclinica della performance emodinamica di valvole polmonari protesiche prevede l’utilizzo di sistemi mock loop in grado di riprodurre la circolazione polmonare umana in vitro. Al fine di ottenere, utilizzando un singolo set-up, sia una misurazione fluidodinamica macroscopica (e.g. pressione e portata), sia parametri dell’emodinamica locale, i sistemi mock loop possono essere integrati a tecniche di imaging, tra cui il 4D-flow acquisito mediante risonanza magnetica (MRI). A tal proposito i circuiti mock loop tradizionali, che generalmente comprendono materiali ferromagnetici, devono essere riadattati all’ambiente della camera di risonanza. La soluzione per la realizzazione di un mock loop MRI compatibile proposta in questo lavoro prevede il posizionamento di una pompa a pistone pulsatile, composta da materiali ferromagnetici, fuori dalla camera di risonanza e connessa al resto del circuito, posizionato sotto lo scanner magnetico, mediante lunghi tubi siliconici. Un’analisi di letteratura ha evidenziato che non sono attualmente presenti simulatori di impedenza polmonare regolabili mediante resistenze lineari. Un processo di dimensionamento e di progettazione dell’afterload polmonare è stato intrapreso in questo lavoro. Sono stati forniti per ogni componente della prevista struttura modulare i corrispondenti ingombri e materiali non ferromagnetici al fine di predisporre le basi per la realizzazione di un simulatore di impedenza polmonare MRI compatibile. In particolare, il sistema di regolazione è stato caratterizzato sperimentalmente, in modo da definirne il range di funzionalità. Il comportamento del concept del mock loop, compreso di sistema pompante proposto e di afterload progettato, è stato valutato mediante un modello a parametri concentrati. Dalle simulazioni è emerso che il sistema è in grado di riprodurre a livello della valvola polmonare gli andamenti di flusso e pressione polmonare fisiologici o patologici utilizzando medium con differenti viscosità. La modularità del mock loop permette di sostituire un singolo componente o una sua parte per regolare la loro influenza sulle forme d’onda generate.
Design of a pulsatile MRI-compatible mock circulation loop for prosthetic pulmonary valve assessment
Albertini, Giulia
2019/2020
Abstract
A preclinical haemodynamic evaluation of a pulmonary prosthetic valve’s performance requires hydraulic circuit, i.e. mock loops, which reproduce in vitro the human pulmonary circulation. To achieve, by using a unique set-up, macroscopic fluid dynamic measurements (e.g. pressure and flow rate) and local haemodynamic parameters, mock loops could be adopted with imaging techniques, such as 4D-flow achieved through magnetic resonance (MRI). Conventional mock loop, since they in general include ferromagnetic materials, have to undergo to an adaptation process to the MRI magnetic environment. The MRI-compatible mock loop proposed in this work consists in placing a pulsatile piston pump, realized with ferromagnetic materials, outside the MRI room and connected with the circuit with long silicon tubes. A literature analysis shows that no adjustable pulmonary impedance simulator that features a linear resistance are available yet. Hence, a dimensioning and designing process is conducted in this work. For each component of the proposed modular structure, encumbrance and non-ferromagnetic materials are supplied, to provide the basis for the manufacturing process of the MRI-compatible adjustable pulmonary impedance simulator. Specifically, the regulator system is characterized by hydraulic experimental tests, which allow to identify its range of functioning. The behaviour of the mock loop, that includes the proposed pumping system and the dimensioned and designed afterload, is evaluated by using a lumped parameter approach. The simulations show that the proposed system is able to reproduce at the pulmonary valve level the pulmonary pressure and flow waveforms either in pathological or physiological conditions by accounting for different working medium viscosity. The modular structure proposed for the mock loop allows to replace one of its components to adjust their influence on the reproduced pulmonary waveforms.File | Dimensione | Formato | |
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https://hdl.handle.net/10589/165498