hepatic and biliary disorders
Imaging Tests of the Liver and Gallbladder
Cholescintigraphy
With the increasing availability of MRCP, the usefulness of HIDA scan has decreased significantly. Cholescintigraphy is done after the patient fasts. An IV technetium-labeled iminodiacetic compound (eg, hydroxy or diisopropyl iminodiacetic acid [HIDA or DISIDA]) is injected; these substances are taken up by the liver and excreted in bile, then enter the gallbladder. In Acute Cholecystitis , which is usually caused by impaction of a stone in the cystic duct, the gallbladder does not appear on a scintigraphic scan because the radionuclide cannot enter the gallbladder. Such nonvisualization is diagnostically quite accurate (except for false-positive results in some critically ill patients). However, cholescintigraphy is rarely needed clinically to diagnose acute cholecystitis. If acalculous cholecystitis is suspected, the gallbladder is scanned before and after administration of cholecystokinin (used to initiate gallbladder contraction). The decrease in scintigraphic counts indicates the gallbladder ejection fraction. Reduced emptying, measured as the ejection fraction, suggests acalculous cholecystitis. Cholescintigraphy also detects bile leaks (eg, after surgery or trauma) and anatomic abnormalities (eg, congenital choledochal cysts, choledochoenteric anastomoses). After cholecystectomy, cholescintigraphy can quantitate biliary flow; biliary flow helps identify papillary stenosis (sphincter of Oddi dysfunction). However, in acute or chronic cholestatic hepatic disorders, cholescintigraphy is not accurate as a diagnostic test because, with cholestasis, hepatocytes excrete lower amounts of the radiotracer into the bile. 