Relationship between abdominal ultrasound and fasting?

Must fast for 8 hrs.: In order for the ultrasound to see deep organs such as the pancreas and aorta, the beam needs to pass through your stomach. If your stomach has food and (invariably also) gas in it, the sound beam cannot penetrate to the deep organs. When you eat, your gallbladder contracts. The gallbladder is best evaluated when it is distended with bile, which takes eight hours to accumulate after eating.

See answer: Fasting allows your gallbladder to expand to the optimum size for evaluation. Also, fasting decreases the amount of stomach and bowel gas that could impede the ultrasound examination.