Nuclear medicine scan for the gallbladder is called a HIDA scan (hepatobiliary iminodiacetic acid scan). The test is most commonly done to look for disease of the gallbladder like inflammation or dysfunction. It is also done to look at the bile ducts or leaks of bile.
How is a HIDA scan done?
This test involves injecting a radiopharmaceutical into your vein by a technologist. This then travels to the liver and bile producing cells. Bile helps with digestion. The radiopharmaceutical then travels into the gallbladder which stores bile. It then travels through the bile duct to the intestine.
The radiopharmaceutical gives off radiation which is imaged with a special camera. There is a normal expected sequence of visualization of the liver, gallbladder, bile ducts, and intestine during the first hour as the radiopharmaceutical moves with the bile.
Why is a HIDA scan ordered?
The most common reason the test is ordered in my experience to look for gallbladder inflammation or cholecystitis. An acutely inflamed gallbladder will not show up on a HIDA scan. The gallbladder normally has a connection with the main bile duct via the cystic duct. When the gallbladder is inflamed, the connection is blocked. The gallbladder will not fill with the radiopharmaceutical. Imaging may be needed for 4 hours to make sure the gallbladder does not fill.
Sometimes the test is done to see how the gallbladder empties. This is called the ejection fraction. Cholecystokinin is a hormone which is injected and stimulates the release of bile into the intestine. Imaging is performed for an hour and the ejection fraction of the gallbladder is calculated. An ejection fraction lower then 40% means there is gallbladder dysfunction.
Bile duct obstruction
The HIDA scan can also tell us if there is bile duct obstruction. The bile duct connects the liver and gallbladder to the intestine. The bile duct can be obstructed from stones, tumors, scarring in addition to other causes. The HIDA scan will show lack of passage of the radiopharmaceutical into the intestine with a complete obstruction. Often imaging with MRI will give us a specific reason for the blockage.
Bile leaks can be diagnosed with HIDA scans. Bile leaks are most common after injury to the bile duct. This is most common with surgery, like when the gallbladder is removed. This can also occur after trauma to the liver. The HIDA scan will show accumulation of the radiopharmaceutical outside the intestines in the abdomen.
HIDA scans are performed by a technologist and interpreted by a radiologist or nuclear medicine physician. The physician may request additional or delayed imaging. HIDA scans can have false positive or false negative results so the clinical team must use all information to reach the correct diagnosis.
A positive HIDA scan for gallbladder inflammation often means surgery is needed. A bile duct blockage also needs an intervention to relive the obstruction. A HIDA scan is therefore an important commonly done test that often has important impact on management.