Contrast enhanced ultrasonography (CEU) involves the intravenous injection of gas-filled microbubbles to enhance the ultrasound image of the organs and mainly to assess tissue vascularity and blood flow. We and others have used CEU to assess changes in RBF in response to physiologic stimuli and therapeutic interventions. Here we propose a prospective, pilot diagnostic study to validate the use of CEU, in assessing RBF in cirrhotic patients with AKI, and to assess the utility of CEU to differentiate between causes of AKI in cirrhotic patients.