A HIDA scan, or hepatobiliary iminodiacetic acid scan, is a specialized nuclear medicine imaging test. It uses a small amount of a radioactive tracer, often a variant of iminodiacetic acid (IDA), injected into the bloodstream. The tracer travels to the liver, gallbladder, bile ducts, and small intestine. A gamma camera captures images of its movement, providing insights into how these organs function in bile production and transport.
Purpose of a HIDA Scan
HIDA scans are performed to investigate problems within the biliary system, which includes the liver, gallbladder, and bile ducts. The scan helps diagnose conditions such as acute cholecystitis, a sudden inflammation of the gallbladder often caused by gallstones blocking the cystic duct. It also helps identify chronic cholecystitis, involving repeated episodes of gallbladder inflammation, usually due to intermittent blockages.
The procedure evaluates the patency, or openness, of the bile ducts and the contractile function of the gallbladder. By tracking the tracer’s movement, doctors can detect obstructions, such as those caused by gallstones, or assess for bile leaks that might occur after surgery or trauma. A HIDA scan can also measure the gallbladder ejection fraction, which indicates how well the gallbladder releases bile, aiding in the diagnosis of functional issues.
The HIDA Scan Procedure
Before a HIDA scan, patients are asked to fast for about four to six hours, though clear liquids may be allowed. It is important to inform the healthcare provider about any medications or supplements, as some might affect the scan’s accuracy. Patients who are pregnant or breastfeeding should also notify their doctor, as the scan may be postponed.
During the procedure, the patient lies on an examination table, and an intravenous (IV) line is inserted. The radioactive tracer is then injected. A gamma camera is positioned over the abdomen to capture images as the tracer moves through the liver, gallbladder, bile ducts, and into the small intestine. Patients must remain still during this imaging process to ensure clear and accurate pictures.
The scan takes about 60 minutes, but it can extend up to a few hours. In some cases, a medication like cholecystokinin (CCK) may be administered to stimulate the gallbladder to contract and release bile. This helps assess the gallbladder’s emptying function and can cause mild abdominal cramping. Morphine may also be given to enhance gallbladder visualization.
Interpreting HIDA Scan Results
The images from a HIDA scan provide a visual representation of bile flow through the biliary system. A normal HIDA scan shows the radioactive tracer moving freely from the liver into the gallbladder and then into the small intestine within approximately one hour. This indicates that the liver, gallbladder, and bile ducts are functioning as expected.
Abnormal findings can point to various issues. If the gallbladder does not visualize, meaning the tracer does not enter it, this suggests an acute inflammation of the gallbladder or an obstruction of the cystic duct, due to gallstones. Slow movement of the tracer through the biliary system can indicate a blockage or a problem with liver function. A low gallbladder ejection fraction, particularly after CCK administration, suggests that the gallbladder is not contracting efficiently, which can be a sign of chronic inflammation. If the tracer is observed outside the normal biliary pathway, it may indicate a bile leak.
Safety and Important Considerations
HIDA scans are generally considered safe, with very few associated risks. The radiation exposure from the tracer is minimal, comparable to annual background radiation. Most of the tracer leaves the body through urine and stool within a day or two, and drinking plenty of water can help expedite its elimination.
Despite the low radiation dose, HIDA scans are not recommended for pregnant individuals due to potential risks to the developing fetus; alternatives like ultrasound or MRI are often considered. Breastfeeding individuals may need to pump and discard breast milk for 1 to 2 days after the scan to prevent contamination. Allergic reactions to the radioactive tracer or other medications used during the scan are rare but can occur, as can minor bruising at the injection site.