A HIDA scan, also known as hepatobiliary iminodiacetic acid scan, is a specialized diagnostic imaging test. This nuclear medicine procedure helps medical professionals evaluate the function of the liver, gallbladder, and bile ducts. It involves introducing a small amount of a radioactive tracer into the body to visualize the pathway of bile. The scan provides insights into how bile is produced, stored, and released.
Why a HIDA Scan is Performed
Medical professionals request a HIDA scan to investigate symptoms suggesting issues with the hepatobiliary system. One of its primary uses is to diagnose acute cholecystitis, which is the sudden inflammation of the gallbladder. The scan helps determine if a blockage in the cystic duct, often caused by gallstones, is preventing bile from entering or leaving the gallbladder.
The scan also detects obstructions in the bile ducts, which can impede the flow of bile from the liver to the small intestine. Such blockages might be caused by gallstones, tumors, or other conditions. By tracking the tracer’s movement, clinicians can identify where the bile flow is impaired.
A HIDA scan can assess the overall function of the gallbladder, even in the absence of acute inflammation. This includes evaluating conditions like chronic cholecystitis, a long-term inflammation, or biliary dyskinesia, where the gallbladder does not contract effectively. The test measures the gallbladder’s ejection fraction, indicating how well it releases bile.
What to Expect During a HIDA Scan
Preparing for a HIDA scan involves a period of fasting, for four to six hours before the procedure. This ensures the gallbladder is relaxed and ready to absorb the tracer. Patients should also inform their healthcare provider about any medications they are taking, as some might need to be temporarily stopped.
Upon arrival, a small amount of a radioactive tracer, such as technetium-99m mebrofenin, is injected into a vein in the arm or hand. This tracer is designed to mimic bilirubin, a component of bile, and is taken up by the liver and excreted into the bile ducts. The injection itself is similar to a routine blood draw.
After the injection, imaging begins using a specialized camera called a gamma camera. This camera detects the gamma rays emitted by the tracer as it moves through the liver, bile ducts, and gallbladder. Images are taken at regular intervals over about 60 to 90 minutes, allowing healthcare professionals to observe the tracer’s path.
An additional medication, like cholecystokinin (CCK) or sincalide, may be administered during the scan. This medication causes the gallbladder to contract, simulating a meal, and helps measure its ejection fraction. Patients might experience a mild cramping sensation or nausea when CCK is given, which is temporary. The total duration of the scan can range from one to four hours, depending on how quickly the tracer moves and if additional imaging is needed.
Understanding HIDA Scan Results
Interpreting HIDA scan results involves observing the tracer’s movement through the hepatobiliary system. A normal result shows the radioactive tracer appearing in the liver, then promptly filling the bile ducts, gallbladder, and finally entering the small intestine within about 60 minutes. This indicates proper bile production, unobstructed flow, and normal gallbladder function.
An abnormal HIDA scan can present in several ways, each pointing to different conditions. If the gallbladder does not visualize within 60 to 90 minutes, especially after the tracer has reached the bile ducts, it suggests acute cholecystitis. This non-visualization indicates a probable blockage of the cystic duct, preventing the tracer from entering the gallbladder.
Delayed visualization of the gallbladder, where it appears much later than expected (e.g., after four hours), can suggest chronic gallbladder inflammation or other long-standing issues. If the tracer does not appear in the small intestine, it may indicate a common bile duct obstruction, preventing bile from flowing into the digestive tract. An abnormally low gallbladder ejection fraction, below 35-38%, points to impaired gallbladder contraction, which can cause symptoms even without a blockage. These findings guide medical professionals in determining the most appropriate course of action, which may include further diagnostic tests or specific treatments.