Inflamed gall bladder. Ultrasound scan of acute cholecystitis (inflammation of the gall bladder) in a 29-year-old woman. The gall bladder (black, oval-shaped, centre) is seen with thickened walls (grey). It is a sac (7-10 centimetres long) that stores bile, a fat-digesting fluid that is made in the liver and passed from the gall bladder to the intestines. Bile is normally clear on ultrasound scans, appearing black. Here, increased brightness shows thickening of the bile. Acute cholecystitis is caused by a bacterial infection. It is treated with rest and antibiotic drugs. Ultrasound scans use reflected high-frequency sound waves to build- up a picture of internal body structures.