A HIDA scan (hepatobiliary iminodiacetic acid scan), also called cholescintigraphy, is performed in order to assess the patency and functioning of the gallbladder and the bile ducts. A radioactive tracer chemical, called iminodiacetic acid, is injected into a vein. Over time, the radioactive chemical goes to the liver and is excreted into the bile ducts. A special scanner that picks up radioactive signals (similar to a Geiger counter) allows the generation of images of the liver, gallbladder, and bile ducts to be recorded. Although the contrast material utilized is radioactive, the scan itself does not involve any radiation exposure to the patient.
HIDA scans are usually done when patients have signs of gallbladder disease, including chronic indigestion, fever, white or clay colored bowel movements, colicky right upper quadrant pain, jaundice, nausea, vomiting.
The gallbladder is an organ that is located behind the liver. It is a muscular pouch that contains fluid called bile which is crucial to the digestion of fats. When crystals form in the bile, the crystals can clump together and create gallstones. Gallstones can irritate the inside of the gallbladder, causing it to become swollen and painful. This condition is called cholecystitis. Gallstones can also block the ducts that lead from the gallbladder, the liver, or the pancreas to the upper part of the small intestine, the duodenum. When this happens, pain in the right upper quadrant of the abdomen can be quite severe. Under very rare circumstances, the obstruction may be caused not by a gallstone, but by the presence of a parasite, blood clot, or tumor. Blockages may also result in jaundice, an increase in bilirubin in the blood which can cause the whites of the eyes and the skin to turn yellow. Sometimes, obstruction of the biliary system leads to bacterial infection, a condition called cholangitis.
Bile— A fluid produced by the liver and stored in the gallbladder. Bile is important for the appropriate digestion of fats in the intestine.
Biliary system— The term used to describe the system of ducts that carries the bile flow through the liver and the gallbladder, and ultimately empties into the duodenum.
Cholangitis— A bacterial infection of the biliary system.
Cholecystitis— Swelling and inflammation of the gall bladder.
Duodenum— The first part of the small intestine. The duodenum receives stomach contents, as well as digestive juices from the gallbladder, liver, and pancreas.
Jaundice— A condition in which elevated bilirubin in the bloodstream causes the whites of the eyes and the skin to turn yellow.
95% of the time, gallbladder inflammation or cholecystitis is due to the presence of gallstones. Gallstones strike about 0.6% of the general population. Some ethnic groups are more prone to gallstones than others (for example, more than 75% of Native Americans over the age of 60 have gallstones). Between the ages of 20 and 60, women are thre times as likley as men to develop gallstones.
During a HIDA scan, a radioactive dye or tracer is injected into a vein in the arm. As the tracer proceeds through the liver, gallbladder, and small intestine, a scanner positioned over the abdomen records a series of images. Scans are preformed at set intervals (usually about every 5-10 minutes) over the course of the 90-minute examination. If the tracer is moving very slowly through the patient’s system, the patient may be asked to return as late as the next day in order to repeat a scan to see whether tracer is still present.
Another chemical, called cholecystokinin or CCK, may also be used during the course of a HIDA scan. CCK stimulates the gallbladder to contract, and images taken following CCK injection can give important information about how well the gallbladder is functioning.
Bismuth (found in certain heartburn medicines) and barium (used to perform x-ray studies such as upper and lower GI series) can both interfere with the scanning results. Therefore, patients should be advised to delay undergoing a HIDA scan by at least four days after the use of bismuth or barium. Patients are also asked to stop eating and drinking during the four to twelve hours prior to the HIDA scan. Women who are breastfeeding and who undergo a HIDA scan should feed their baby with formula for two days following the procedure, and should pump and discard their breast milk, since it will be contaminated with the radioactive dye.
Patients are often asked to eat a fatty meal the night before having a HIDA scan.
There is no aftercare necessary following a HIDA scan. The patient can return to a normal diet and normal activities.
HIDA scans pose very little risk to the patient, although some patients do experience pain during the course of the exam, due to contraction of the inflamed gall bladder. Under rare circumstances, patients may exhibit signs of allergy to the tracer.
Normal results of a HIDA scan show the gallbladder in the appropriate anatomical location, with normal measurements and shape. Scanning over time reveals that the tracer progresses in an appropriate and timely fashion through the liver, into the gallbladder, and then into the duodenum.
A HIDA scan is abnormal when the gallbladder is not normal size, or if a blockage (from either a gallstone or inflammation) prevents the gallbladder or duodenum from being visualized because the tracer cannot flow freely through the normal route. Liver disease may be present if the liver does not take up the tracer from the bloodstream. If tracer is evident outside of the usually path of the biliary system, there may be some kind of a leak from the bile ducts or the gallbladder. If cholecystokinin has been administered, swelling or scarring of the gallbladder wall may be indicated by the continued presence of radioactive tracer in the gallbladder, which cannot perform its normally activity of contracting to empty bile into the duodenum.
Feldman, M., et al.Sleisenger & Fordtran’s Gastrointestinal and Liver Disease. 8th ed. St. Louis: Mosby, 2005.
Grainger, R. G., et al. Grainger & Allison’s Diagnostic Radiology: A Textbook of Medical Imaging. 4th ed. Philadelphia: Saunders, 2001.
Mettler, F. A. Essentials of Radiology, 2nd ed. Philadelphia: Saunders, 2005.
Rosalyn Carson-DeWitt, MD