Hepatobiliary scan

The Hepatobiliary Scan, commonly referred to as a HIDA scan (Hepatobiliary Iminodiacetic Acid scan), is a specialized nuclear medicine test used to evaluate the functionality of the liver, gallbladder, and bile ducts. This system, known as the hepatobiliary system, plays a crucial role in the production, storage, and excretion of bile, which helps in fat digestion and the removal of metabolic waste. A HIDA scan allows clinicians to trace the flow of bile from the liver through the bile ducts into the small intestine, identifying any functional blockages, leakage, or delayed emptying. This scan is often requested when there is unexplained upper abdominal pain, jaundice, or suspicion of gallbladder dysfunction or bile duct obstruction. The procedure is non-invasive, safe, and extremely useful in evaluating both acute and chronic hepatobiliary diseases, especially when other imaging techniques like ultrasound, CT, or MRI fail to provide definitive answers.

What is the Hepatobiliary System?

1. The liver produces bile—a yellowish-green fluid that aids in digesting dietary fats and removing toxins from the body.
2. This bile flows through bile ducts into the gallbladder, where it is stored until needed.
3. Upon eating, the gallbladder contracts and releases bile into the small intestine through the common bile duct.
4. Proper flow and regulation of bile are essential for digestion and liver health. Any disruption in this flow can result in conditions such as biliary atresia, cholecystitis, bile leaks, or gallbladder dysfunction.

What is a HIDA Scan?

• A HIDA scan uses a small amount of a radioactive tracer (usually Technetium-99m-labeled iminodiacetic acid derivative) that mimics the path of bile.
• Once injected into a vein, this tracer is taken up by hepatocytes (liver cells), secreted into the bile, and follows its natural pathway through the biliary system.
• A gamma camera captures images in real-time, allowing visualization of bile production, storage, and excretion.
• In some cases, additional medications such as cholecystokinin (CCK) or morphine are administered to assess gallbladder contraction or improve visualization of bile ducts.

Indications for a HIDA Scan

A hepatobiliary scan may be recommended in several clinical scenarios, such as:

• Evaluation of acute or chronic cholecystitis (gallbladder inflammation)
• Assessment of biliary atresia vs neonatal hepatitis in infants with prolonged jaundice
• Gallbladder ejection fraction (GBEF) measurement in suspected biliary dyskinesia
• Investigation of right upper quadrant pain with normal ultrasound findings
• Assessment of bile leaks following liver or gallbladder surgery
• Monitoring of liver transplant function
• Evaluation of biliary obstruction or stenosis
• Functional analysis in sphincter of Oddi dysfunction or biliary pain syndromes

How the Procedure is Performed

1. The patient is positioned under a gamma camera in a comfortable, supine position.
2. An intravenous injection of a radiopharmaceutical agent (Tc-99m HIDA compound) is administered.
3. Dynamic imaging begins immediately and continues for 60–90 minutes, tracking the tracer’s journey through the liver, gallbladder, and bile ducts.
4. In some cases, delayed images at 2–4 hours may be required to evaluate bile flow in slow or borderline cases.
5. If gallbladder ejection fraction (GBEF) is being assessed, a fatty meal or cholecystokinin (CCK) may be given mid-scan to stimulate gallbladder contraction.
6. Morphine may be administered to increase pressure at the sphincter of Oddi, helping force bile into the gallbladder and improve visualization.

Gallbladder Ejection Fraction (GBEF)

One of the most valuable components of a HIDA scan is the calculation of GBEF, which helps evaluate gallbladder contractility:

• A normal GBEF is considered to be above 35–40%.
• A reduced GBEF suggests biliary dyskinesia or functional gallbladder disorder, where the gallbladder does not empty properly even without gallstones. 
• This is particularly helpful in patients who experience recurrent biliary colic but have a normal ultrasound.

Comparison with Other Imaging Techniques

While a HIDA scan is functional, other modalities like ultrasound, CT, and MRI provide anatomical views:

• Ultrasound is the first-line modality for evaluating gallstones and gallbladder wall thickening but cannot assess gallbladder function.
• CT scans are useful in identifying biliary obstruction, tumors, or infections but lack detail about bile flow.
• MRCP (Magnetic Resonance Cholangiopancreatography) provides high-resolution images of bile ducts but does not offer real-time data on bile movement.
• HIDA scan stands out for its ability to show functional abnormalities—e.g., delayed bile excretion, gallbladder non-visualization, or leakage—that are often missed on structural imaging.

Advantages of HIDA Scan

• Provides real-time functional imaging of the liver and biliary system
• Detects acute cholecystitis with high sensitivity and specificity
•  Evaluates postoperative bile leaks after surgery or trauma
• Measures gallbladder contractility (GBEF) non-invasively
• Differentiates biliary atresia from neonatal hepatitis in infants
• Assesses liver transplant function
• Non-invasive and minimal discomfort
• Safe for both adults and pediatric patients

Limitations

1. False negatives may occur if recent food or medications interfere with gallbladder contraction.
2. May not identify very small stones or strictures, which may require adjunct imaging.
3. Not recommended during pregnancy unless absolutely necessary.
4. Results can be affected by fasting status, liver function, or obstructive disease.

Safety and Preparation

• The procedure is very safe with minimal radiation exposure.
• The radiopharmaceutical used has no known serious side effects.
• Patients are advised to fast for 4–6 hours before the scan to ensure accurate results.
• Some medications, especially opioids or gallbladder-affecting drugs, may need to be paused prior to the scan (under physician guidance).
• Post-test, patients can resume normal diet and activity. Drinking extra water is encouraged to help clear the tracer from the body.

Results and Interpretation

A nuclear medicine specialist will interpret the scan and evaluate:

• Time taken for liver uptake of the tracer
• Visualization of the gallbladder and small intestine
• Time of bile duct emptying
• Gallbladder ejection fraction (if performed)
•  Presence of any leaks, obstructions, or non-functioning areas

Results are usually available within 24 hours and help guide surgical, medical, or endoscopic management.

Conclusion

The Hepatobiliary (HIDA) scan is an essential tool in the functional evaluation of the liver, gallbladder, and bile ducts. Unlike anatomical imaging modalities, this test provides a dynamic assessment of bile flow, enabling clinicians to accurately diagnose cholecystitis, biliary dyskinesia, bile leaks, and post-transplant complications. Its ability to measure gallbladder ejection fraction and detect functional abnormalities makes it invaluable in the workup of patients with unexplained right upper quadrant pain, jaundice, or suspected gallbladder disease. When performed at the right time and interpreted properly, a HIDA scan can avoid unnecessary surgeries, guide effective treatment, and significantly improve patient outcomes.