A HIDA scan is a specialized diagnostic imaging test used to assess the function of the biliary system. This system includes the liver, which produces bile; the bile ducts that transport it; the gallbladder, which stores it; and the small intestine, where bile aids in digestion. The scan evaluates how these organs produce, store, and release bile.
How a HIDA Scan Works
A HIDA scan, also known as hepatobiliary iminodiacetic acid scan or cholescintigraphy, utilizes a small amount of a radiotracer. This radiotracer, commonly technetium-99m labeled with iminodiacetic acid, is injected intravenously into the bloodstream. Once injected, the tracer mimics the natural flow of bile, traveling through the liver, bile ducts, gallbladder, and into the small intestine.
A specialized camera, known as a gamma camera, is positioned over the abdomen to detect the gamma rays emitted by the tracer. These are then converted into images, allowing medical professionals to observe the tracer’s pathway and assess bile production and flow dynamics. This provides insights into the functional status of the biliary system, helping to identify potential abnormalities.
Key Conditions Identified
A HIDA scan helps diagnose several conditions affecting the biliary system. One common diagnosis is acute cholecystitis, a sudden inflammation of the gallbladder. If the gallbladder does not visualize on the scan, it indicates a blockage of the cystic duct, typically caused by gallstones, preventing tracer entry.
The scan also identifies chronic cholecystitis, a long-standing inflammation of the gallbladder. When cholecystokinin (CCK) is administered during the scan to stimulate gallbladder contraction, a low gallbladder ejection fraction (GBEF) can suggest chronic inflammation or functional issues like biliary dyskinesia, indicating inefficient bile emptying.
HIDA scans are valuable for detecting bile duct obstructions. If the radiotracer shows slow movement or fails to pass into the small intestine, it suggests a blockage within the bile ducts, possibly from gallstones or other issues. Tracer outside normal biliary pathways indicates a bile leak, often a complication following surgery or trauma. In infants, the scan can diagnose congenital abnormalities like biliary atresia, where bile ducts are underdeveloped or absent.
What to Expect During the Scan
During a HIDA scan, patients typically lie on their back on an examination table. An intravenous (IV) line is inserted into a vein, usually in the arm, for radiotracer injection. A gamma camera is positioned over the abdomen to capture images as the tracer moves through the biliary system.
Patients must remain as still as possible during imaging to ensure clear pictures. The scan typically lasts one to four hours, though delayed images may be required up to 24 hours later.
If the scan includes an assessment of gallbladder function, cholecystokinin (CCK) may be administered via the IV to stimulate gallbladder contraction. This may cause mild abdominal cramps, similar to discomfort after a fatty meal. The procedure is generally painless, but existing pain from the underlying condition may persist.
Preparing for Your HIDA Scan
Preparation is important for an accurate HIDA scan. Patients must fast for four to twelve hours before the scan to ensure the gallbladder is empty and responsive. Fasting over 24 hours can lead to inaccurate results if the gallbladder does not fill.
Discuss all current medications with your healthcare provider, as some, particularly opioid pain relievers, can interfere with scan results and may need to be temporarily stopped. Pregnant or breastfeeding patients must inform medical staff, as the radiotracer could affect the fetus or pass into breast milk, possibly requiring scan postponement or temporary breastfeeding cessation.
Wear comfortable, loose-fitting clothing and remove any jewelry or metal objects from the abdominal area, as these can interfere with imaging equipment. Specific instructions will be provided by your healthcare provider or imaging center.