The initial diagnostic test for acute pancreatitis is usually an abdominal ultrasound. An abdominal ultrasound is a noninvasive imaging test that uses high-frequency sound waves to create a picture of the structures inside the abdomen, including the pancreas. An abdominal ultrasound can show inflammation in the pancreas, as well as any blockages or abnormal growths. Ultrasounds can also detect fluid buildup in the abdomen, which is a sign of acute pancreatitis. Other tests that may be used to diagnose acute pancreatitis include blood tests, CT scans, and MRI scans.