The HIDA scan is most accurate in estab-lishing a diagnosis of acute cholecystitis. After injection, the technetium-labeled imminodi-acetic acid radioisotopes are taken up by the liver and excreted into the biliary tree. If the cystic duct is obstructed (as in patients with acute cholecystitis) the gallbladder will not be visualized. Ultrasound may show ductal dilation, the presence of wall thickening (<3 mm), or pericholecystic fluid, which is highly suggestive of acute cholecystitis