Hepatic artery and portal flows are both regulated to assume the whole hepatic blood flow. Each counts for respectively 25% and 75%. That so-called "buffer response" assumes that when portal flow increases, hepatic artery flow decreases. During fluid challenge in intensive care unit, fluid challenge is often administered to improve hepatic perfusion. That observation is not demonstrated. The aim of the study is to test buffer response and portal flow during fluid challenge.

Prospective monocentric study at Amiens Hospital University. 20 volunteers subjects will be include after providing informed consent. Fluid challenge will be performed with 500 ml of intra venous NaCl (0.9%). Hepatic blood flow measurement will be performed using MRI.

Inclusion Criteria:

• Fasting for the last 12 hours.

Exclusion Criteria:

• Claustrophobia
• Any previous medical history disease;
• Any abdominal surgical disease
• Pregnancy or breastfeeding