Magnetic Resonance Elastography and Portal Hypertension: Influence of the Portal Venous Flow on the Liver Stiffness
Résumé
The invasive measurement of the hepatic venous pressure gradient is still considered as the reference method to assess the severity of portal hypertension. Even though previous studies have shown that the liver stiffness measured by elastography could predict portal hypertension in patients with chronic liver disease, the mechanisms behind remain today poorly understood. The main reason is that the liver stiffness is not specific to portal hypertension and is also influenced by concomitant pathologies, such as cirrhosis. Portal hypertension is also source of a vascular incidence, with a substantial diversion of portal venous blood to the systemic circulation, bypassing the liver. This study focuses on this vascular effect of portal hypertension. We propose to generate and control the portal venous flow (to isolate the modifications in the portal venous flow as single effect of portal hypertension) in an anesthetized pig and then to quantify its implications on liver stiffness by an original combination of MRE and 4D-Flow Magnetic Resonance Imaging (MRI). A catheter balloon is progressively inflated in the portal vein and the peak flow, peak velocity magnitude and liver stiffness are quantified in a 1.5T MRI scanner (AREA, Siemens Healthcare, Erlangen, Germany). A strong correlation is observed between the portal peak velocity magnitude, the portal peak flow or the liver stiffness and the portal vein intraluminal obstruction. Moreover, the comparison of mechanical and flow parameters highlights a correlation with the possibility of identifying linear relationships. These results give preliminary indications about how liver stiffness can be affected by portal venous flow and, by extension, by hypertension.