A hepatobiliary iminodiacetic acid scan, commonly known as a HIDA scan, is a diagnostic imaging procedure. This test evaluates the function of the liver, gallbladder, and bile ducts, helping medical professionals understand how bile is produced, stored, and flows through the body’s biliary system. Also referred to as cholescintigraphy or hepatobiliary scintigraphy, the HIDA scan uses a small amount of a radioactive substance to create images.
Why a HIDA Scan is Performed
A HIDA scan is often performed to investigate the cause of abdominal pain, particularly in the upper right side, which may indicate issues with the gallbladder or bile ducts. A primary reason for this scan is to diagnose gallbladder inflammation, known as cholecystitis. This condition can be acute, appearing suddenly, or chronic, involving repeated episodes of inflammation.
The scan also helps identify blockages within the bile ducts, which can prevent bile from flowing properly from the liver to the small intestine. Such obstructions can be caused by gallstones or other factors. Furthermore, a HIDA scan assesses liver function related to bile production and flow, and can evaluate congenital problems like biliary atresia in newborns, where bile ducts are abnormally formed. It can also be used to check for bile leaks or fistulas that may occur after surgery, and to monitor the function of a liver transplant.
Preparing for the Scan
Preparing for a HIDA scan involves a few specific instructions to ensure accurate results. Patients are typically required to fast for at least four hours before the scan, consuming no food or drink other than water. Some medical providers may allow clear liquids, but solid food should be avoided.
It is also important to inform the medical team about any medications being taken, especially opioid or morphine-based pain medications, as these might interfere with the scan results and should be avoided for a period before the test. Additionally, individuals who are pregnant or breastfeeding should notify their doctor, as the radioactive tracer can affect a fetus or be present in breast milk.
The Scan Procedure Explained
The HIDA scan procedure begins with the patient lying on an examination table. A healthcare professional will insert an intravenous (IV) catheter into a vein in the arm or hand. This IV line is used to administer a small amount of a radioactive tracer, specifically technetium-99m iminodiacetic acid (Tc-99m HIDA), into the bloodstream.
Once injected, this tracer travels through the bloodstream to the liver, where it is taken up by bile-producing cells and excreted into the bile ducts. A special imaging device called a gamma camera is positioned over the abdomen to track the tracer’s movement. This camera detects the gamma rays emitted by the tracer, creating a series of images that show its journey from the liver, through the bile ducts, into the gallbladder, and eventually into the small intestine.
The imaging process can take anywhere from one to four hours, depending on how quickly the tracer moves through the system and whether additional images are needed. During this time, it is important for the patient to remain still to ensure clear images. In some cases, a medication called cholecystokinin (CCK), or sincalide, may be administered during the scan. This hormone causes the gallbladder to contract and release bile, which helps assess its ability to empty, a measurement known as the gallbladder ejection fraction.
Interpreting Your Results
Medical professionals interpret HIDA scan results by observing the flow and accumulation of the radioactive tracer within the biliary system. A normal result indicates that the tracer moved freely from the liver into the gallbladder and then into the small intestine. This suggests proper function of the liver, bile ducts, and gallbladder.
Abnormal findings can suggest various issues. If the tracer moves slowly, it might indicate a blockage in the bile ducts or a problem with liver function. If the gallbladder does not fill with the tracer at all, this often points to acute cholecystitis, which is severe inflammation of the gallbladder, usually due to a blockage.
A low gallbladder ejection fraction, assessed when CCK is administered, suggests that the gallbladder is not contracting efficiently. This can be a sign of chronic gallbladder inflammation. If the tracer is detected outside the normal biliary pathway, it may indicate a bile leak.