A HIDA scan, formally known as a Hepatobiliary Iminodiacetic Acid scan, is a specialized imaging procedure that evaluates the function of the liver, gallbladder, bile ducts, and small intestine. This non-invasive tool visualizes the flow of bile, a digestive fluid produced by the liver, through the biliary system. By tracking bile’s path, the HIDA scan helps identify various issues affecting these organs.
Understanding the HIDA Scan
A HIDA scan is a nuclear medicine imaging test that assesses liver, bile duct, and gallbladder function. It involves injecting a small amount of a radioactive tracer, typically technetium-99m, into the bloodstream. This tracer mimics bilirubin, allowing it to be absorbed by the liver and excreted into the bile ducts.
As the tracer moves through the biliary system, a gamma camera detects the emitted gamma rays. These signals are converted into images, allowing medical professionals to observe the tracer’s journey from the liver, into the gallbladder, and through the bile ducts to the small intestine. This tracking reveals the patency of the bile ducts and the functional capacity of the gallbladder.
The primary purpose of a HIDA scan is to assess bile flow and identify obstructions, inflammation, or other functional issues within the biliary system. It frequently diagnoses conditions such as acute cholecystitis, which is sudden inflammation of the gallbladder often caused by a blockage. The scan can also detect chronic cholecystitis and assess for bile leaks, which can occur after surgery or injury.
A HIDA scan also evaluates the gallbladder’s ejection fraction, measuring how effectively it contracts and releases bile. This measurement is useful in diagnosing conditions like biliary dyskinesia, where the gallbladder’s ability to empty is impaired without a clear obstruction. The HIDA scan offers a detailed picture of biliary system health, complementing structural imaging tests like ultrasound.
Preparing for and Undergoing the Scan
Patients are required to fast for at least four to six hours before the procedure, consuming no food or drink except water. This fasting ensures the gallbladder is relaxed and ready to fill with the radiotracer, preventing false readings.
Inform your healthcare provider about any medications, especially opiate-based pain relievers. Certain medications, such as morphine or codeine, can affect the bile ducts and interfere with scan accuracy. You may be advised to stop taking them for a period, often six to 24 hours, before the test.
During the procedure, you will lie on a table, and a small amount of radioactive tracer will be injected into a vein in your arm. A gamma camera will then be positioned over your abdomen to capture images as the tracer moves through your liver, gallbladder, and bile ducts.
The imaging process typically takes 60 to 90 minutes, though it may extend up to four hours. Remain as still as possible to ensure clear images. In some instances, medication like cholecystokinin (CCK) or morphine may be administered intravenously to stimulate gallbladder contraction or aid visualization, which might cause mild abdominal cramping.
Interpreting Your HIDA Scan Results
After the HIDA scan, a healthcare professional, often a radiologist, interprets the images to assess radiotracer flow through your biliary system. A normal HIDA scan indicates the tracer moved smoothly from your liver, filled your gallbladder, and then passed into your small intestine. This pattern suggests your liver is producing bile effectively, your bile ducts are open, and your gallbladder is functioning correctly by filling and emptying as expected.
Abnormal results can point to various issues. If the radiotracer does not appear in the gallbladder within one to four hours, it can suggest an obstruction of the cystic duct, often associated with acute cholecystitis. This non-visualization occurs because the tracer cannot enter the blocked gallbladder.
Slow movement or delayed filling may indicate a partial blockage, reduced liver function, or chronic gallbladder inflammation. If the gallbladder fills but empties slowly after CCK stimulation, it might suggest a functional problem, such as chronic cholecystitis or biliary dyskinesia. If the tracer is seen outside the expected pathway, it could indicate a bile leak. Findings are considered alongside symptoms and other diagnostic tests for a comprehensive diagnosis.
Safety Considerations
HIDA scans are generally safe procedures with minimal risks. The primary concern involves exposure to a small amount of radiation from the injected radiotracer. The radiation dose is comparable to natural background radiation an average person receives in a year, or a head CT scan. The radioactive material loses reactivity quickly and is eliminated from the body primarily through urine and stool within a day or two.
Patients may experience minor side effects, such as bruising or slight discomfort at the injection site. Allergic reactions are extremely rare. If CCK is used, some individuals might experience temporary abdominal cramping or nausea, which typically subsides quickly.
Medical professionals take precautions to minimize radiation exposure, and the benefits generally outweigh these small risks. HIDA scans are typically avoided during pregnancy due to potential risks to the developing fetus. Inform your healthcare provider if you are pregnant, suspect you might be pregnant, or are breastfeeding, as alternative diagnostic methods may be considered.