A nuclear medicine (NM) hepatobiliary scan is an imaging test that tracks bile as it moves from your liver through your bile ducts and into your gallbladder and small intestine. It’s most commonly used to diagnose gallbladder inflammation, bile duct blockages, and bile leaks after surgery. You may also hear it called a HIDA scan, cholescintigraphy, or hepatobiliary scintigraphy.
Unlike an ultrasound or CT scan, which show the physical structure of your organs, a hepatobiliary scan shows how well those organs are actually working. It can detect problems like a blocked bile duct before any structural changes become visible on other imaging.
How the Scan Works
The test uses a small amount of radioactive tracer injected into a vein in your arm. This tracer is designed to mimic bilirubin, a substance your liver naturally processes and excretes into bile. Once injected, the tracer binds to a protein in your blood, travels to your liver, gets picked up by liver cells, and is released into your bile ducts, just like real bile would be.
A special gamma camera positioned over your abdomen detects the radiation from the tracer as it moves through your system. This produces a series of images showing the tracer flowing from your liver into your bile ducts, filling your gallbladder, and eventually passing into your small intestine. If the tracer gets stuck, fails to reach certain areas, or leaks where it shouldn’t, that tells the radiologist something specific is wrong.
Conditions It Diagnoses
The most common reason for ordering a hepatobiliary scan is suspected acute cholecystitis, which is sudden gallbladder inflammation usually caused by a gallstone blocking the duct that connects the gallbladder to the rest of the bile system. When that duct is blocked, the tracer never reaches the gallbladder. Persistent nonfilling of the gallbladder on the scan is diagnostic for acute cholecystitis and can be detected immediately after the blockage begins.
Beyond acute gallbladder problems, the scan can evaluate:
- Chronic gallbladder disease: The gallbladder may fill but empty poorly, or fill in an irregular pattern.
- Bile duct obstruction: Reduced or absent flow through the ducts, sometimes detectable before the ducts even appear dilated on ultrasound.
- Bile leaks: After gallbladder surgery or liver procedures, the tracer may appear outside the expected pathway, pinpointing the leak.
- Biliary atresia: In newborns with prolonged jaundice, the scan helps determine whether bile ducts are absent or nonfunctional.
- Sphincter of Oddi dysfunction: The muscle controlling bile flow into the intestine may not open properly.
What Happens During the Procedure
You’ll need to fast for several hours before the scan, typically four to six hours, so that bile has time to accumulate in your gallbladder. If you’ve eaten recently, the gallbladder may have already emptied, which can make the images harder to interpret.
At the appointment, you’ll lie on a table while a technologist injects the tracer into your arm. The gamma camera is positioned close to your abdomen but doesn’t touch you. Imaging starts shortly after the injection, and the camera captures a series of pictures as the tracer moves through your system. The whole process typically takes one to four hours. In some cases, you may need to return for additional images up to 24 hours later.
If the gallbladder hasn’t filled after about an hour and there’s no sign of a bile duct blockage, you may be given a low dose of morphine through your IV. This causes the muscle at the end of the common bile duct to tighten, which redirects bile flow toward the gallbladder. If the gallbladder still doesn’t fill after morphine, the scan is considered positive for acute cholecystitis.
Gallbladder Ejection Fraction
When chronic gallbladder disease is suspected, the scan often includes a second phase to measure how well the gallbladder contracts. After the tracer fills the gallbladder, you’re given a hormone through your IV that triggers the gallbladder to squeeze. The camera measures what percentage of bile the gallbladder empties. This number is your gallbladder ejection fraction.
A normal ejection fraction is generally 38% or higher, though some studies define the lower cutoff at 35%. An abnormally low number suggests the gallbladder isn’t emptying well, which can cause symptoms like pain after eating, bloating, and nausea even when no gallstones are present. This measurement is one of the key factors in deciding whether gallbladder removal might relieve your symptoms.
Use in Newborns
In infants with persistent jaundice, a hepatobiliary scan helps distinguish biliary atresia, a serious condition where bile ducts are missing or damaged, from other causes of newborn jaundice like neonatal hepatitis. The key finding is whether any tracer makes it into the intestines. If no bile reaches the bowel, biliary atresia is the likely diagnosis.
The scan is highly sensitive for this purpose, correctly identifying about 95% of infants who actually have biliary atresia in one retrospective study. Its negative predictive value is also strong at 96%, meaning a normal result makes biliary atresia very unlikely and can spare infants from more invasive testing. The main limitation is that other causes of newborn cholestasis can mimic biliary atresia on the scan, leading to some false positives. Doctors often combine scan results with blood markers to improve accuracy.
Safety and Side Effects
The radioactive tracer has a half-life of about six hours, meaning it loses half its radioactivity in that time and is rapidly cleared from your body. The radiation dose is low, comparable to what you’d receive from other routine diagnostic imaging. Drinking extra fluids after the scan helps flush the tracer from your system faster.
Side effects are uncommon. The tracer can occasionally cause mild nausea, abdominal discomfort, or a rash. Serious allergic reactions are rare. If morphine is used during the scan, you might experience temporary nausea or lightheadedness. The test itself is painless beyond the initial needle stick, and there are no activity restrictions afterward.
How Results Are Reported
A radiologist reviews the images and looks at several key features: how quickly the liver takes up the tracer, whether the bile ducts are visible and unobstructed, whether the gallbladder fills, and whether tracer reaches the small intestine within a normal timeframe.
A normal scan shows the tracer moving smoothly from the liver through the bile ducts, filling the gallbladder, and entering the small intestine. Abnormal findings vary depending on the condition being evaluated. In acute cholecystitis, the gallbladder simply never appears. In a bile duct obstruction, the tracer may pool in the liver or ducts without passing through. In chronic gallbladder disease, you might see delayed or irregular filling of the gallbladder, slow transit into the intestine, a low ejection fraction, or some combination of these patterns. For suspected bile leaks, tracer appearing outside the normal biliary pathway confirms the diagnosis and helps localize the leak.