|Tipo di tesi||Tesi di dottorato di ricerca|
|Titolo||Caratterizzazione della risposta emodinamica nel distretto epatico mediante tecniche di perfusione e angiografia MRI|
|Titolo in inglese||Hepatic hemodynamic characterization through MR perfusion and angiography techniques|
|Settore scientifico disciplinare||FIS/07 - FISICA APPLICATA (A BENI CULTURALI, AMBIENTALI, BIOLOGIA E MEDICINA)|
|Corso di studi||Scuola di D.R. in MODELLISTICA, SIMULAZIONE COMPUTAZIONALE E CARATTERIZZAZIONE MULTISCALA PER LE SCIENZE DEI MATERIALI E DELLA VITA|
|Data inizio appello||2016-03-04|
|Disponibilità||Accessibile via web (tutti i file della tesi sono accessibili)|
Nel corso degli ultimo anni, molti sforzi sono stati profusi per conoscere più approfonditamente la cirrosi epatica e una delle sue occorrenze più comuni: l’ipertensione portale, ovvero l’incremento della pressione nella vena porta.
During the last years a lot of efforts have been produced to understand cirrhosis liver disease and one of its most common sign: the portal hypertension, i.e. the increase of the pressure in the portal vein. TIPS (Transjugular Intrahepatic Portosystemic Shunt) procedure implies the positioning of an artificial channel that connects the portal vein with the liver outflow vein. Such shunts are known to be efficacious in reducing portal venous pressure and controlling complications, nonetheless they have been associated with significant problems such as poor shunt durability and increased encephalopathy. The appearance on the market of new shunts with adjustable diameter triggered a new impulse for the development of diagnostic techniques able to forecast and monitor hepatic hemodynamic, possibly modifying shunt diameter on a patient specific basis for a better outcome. From a hemodynamic point of view, addressing this issue is a high demanding challenge because of the double vascular inflow (arterial and venous inflow with different pattern in pressure and flow volume) and because of the compensatory system named HABR (hepatic arterial buffer response) that comes into play both in ordinary situation (e.g. after a meal) and in pathological diseases. Actually, procedures able to measure the liver blood inflow are invasive and limited to the venous inflow such as the "thermodiluition catheter technique". Non-invasive diagnostic techniques commonly in use for others body districts are now under investigation for the analysis of liver hemodynamic: - Phase Contrast Magnetic Resonance Angiography (PC-MRI), a MR technique that allows a non invasive measurement of the flow in major vessels; - Perfusion Dynamic Contrast Enhanced – MRI (DCE-MRI), a technique that tries to quantify the microcirculatory status of an organ by means of a 4D dynamic acquisition and a contrast agent gadolinium based injection. To process liver perfusion DCE-MRI data, several models have been proposed, differing for the number of inflow vessels – typically one input (only portal flow) or two inputs (both portal and arterial flow) - or for the number of liver’s compartments, specifically one or two in “Mono Compartment” and “Dual Compartment” models respectively. In this work, data were acquired with DCE-MRI and PC-MRI techniques in patient with cirrhosis disease immediately before and after TIPS implant. From theory and experimental data it was possible to determine an uncertainty level for each output parameter. The analysis of DCE-MRI data - processed with Dual Input Mono Compartment and Dual Input Dual Compartment models- showed that DCE-MRI is a robust technique able to measure liver perfusion parameters. The comparison between PC-MRI data and invasive measurements of portal flow obtained with the thermodilution catheter technique made possible to quantify the MRI data uncertainty, promoting PC-MRI as a standard tool to measure flow also in structure like the liver being affected by cardiac and respiratory movements. Thanks to the obtained results, the evaluation of changes in hepatic hemodynamic due to TIPS implant could be assessed. In particular, after TIPS implant, though portal flow increases, almost all of the his blood drains through the shunt and not in every case the hepatic artery is able to compensate for lack of venous supply; the Mean Transit Time (MTT), that is the time the blood remains in liver, increases, but according to the “Dual Input Dual Compartment model” the MTT of the vascular part decreases. The results of this work can therefore lead to a new approach to TIPS implant, like diameter customization during a follow up based on the DCE-MRI and the PC-MRI datasets analysis.