Nobody walks into an emergency room saying “help! I’ve got cholecystitis!” As with most abdominal emergencies, the patient will describe various symptoms (including abdominal pain, naturally), which help the emergency physician and radiologist to decide which method to use, in order to find the problem. If the radiologist suspects a problem with the gallbladder, then the method of choice is very often ultrasound, which uses soundwaves to produce pictures.
This patient has acute cholecystitis, with a gallstone in the gallbladder (yellow arrow). There is sludge (star) in the gallbladder and thickening of the wall of the gallbladder. The fluid around it (white arrows) is a sign of inflammation.