Overview of Hepatobiliary Scintigraphy
Hepatobiliary scintigraphy is a special type of imaging test used to examine the liver and bile duct system. This method uses a tracker or “radiotracer” that works its way through your body and allows doctors to capture images of these organs. The first tracker used for this test was a compound called iminodiacetic acid (IDA). After it was observed that IDA is effective in visualizing the liver and bile ducts, this test is often referred to as a HIDA scan. Over time, the original compound has been tweaked, and the first version is no longer available for commercial use. These tracers, including the modern ones used today, are injected into your bloodstream, travel to your liver, and then move into your bile duct system. They follow the same path as bilirubin, which is a substance your liver makes and gets rid of through the bile. This is why this test has been so useful in identifying diseases like acute cholecystitis (inflamed gallbladder), chronic gallbladder disease, bile leaks, blockages in the bile ducts, and a condition called biliary atresia which is a blockage in the ducts that carry bile from the liver to the gallbladder.
For the initial examination of suspected gallbladder diseases, an ultrasound is typically the first test utilized. An ultrasound is a more readily accessible test, faster to perform, doesn’t need a lot of preparation, and avoids the use of radiation. It might also point doctors in the direction of other possible diagnoses. However, it may not be as sensitive or accurate in assessing gallbladder diseases, so the Hepatobiliary scintigraphy or HIDA scan remains an essential part of evaluating patients who have upper right abdominal pain or other signs of liver or gallbladder disease.
Anatomy and Physiology of Hepatobiliary Scintigraphy
The biliary system is a network of organs and tubes, including the gallbladder and ducts, that make and move a substance called bile. Bile is produced by liver cells and then gets sent into tiny tube-like structures called biliary canaliculi. These tiny tubes combine to form bigger pipes called intralobular and interlobular ducts. These further combine into left and right hepatic ducts, which are primary passageways leading out of the liver.
These two ducts join together to form the common hepatic duct, which then combines with the cystic duct coming from the gallbladder, forming the common bile duct. This common bile duct runs next to the hepatic artery and portal vein, inside a region called the portahepatis. It then merges with the pancreatic duct and enters into the second part of the small intestine through an opening called the ampulla of Vater. Surrounding this opening is a muscle called the sphincter of Oddi, which controls when the bile can enter the small intestine by opening and closing the ampulla.
Why do People Need Hepatobiliary Scintigraphy
Hepatobiliary scintigraphy is a test that checks the health and function of liver cells, bile ducts, gallbladder, and the sphincter of Oddi (a muscle that controls the flow of digestive juices from the pancreas and gallbladder into the intestines). This test can help doctors diagnose several health issues, including:
- Acute cholecystitis, which is sudden inflammation of the gallbladder. This can be caused by gallstones (calculous) or due to bile build-up (acalculous).
- Chronic gallbladder disease, also known as functional gallbladder disease or chronic cholecystitis, which is a long-lasting inflammation of the gallbladder.
- Biliary leak, which occurs after damage to the bile ducts. This is often seen after gallbladder removal or liver surgery, and following liver injuries.
- Biliary obstruction, which is a blockage in the bile ducts. This can be caused by gallstones, narrowing of the ducts, tumors in the bile ducts or pancreas, and problems with the sphincter of Oddi.
- Biliary atresia, a rare birth defect that if not corrected can cause severe liver damage. Surgery during the first few months of life can prevent major damage, and allows the child to grow and eventually receive a liver transplant if necessary.
Acute cholecystitis is a common reason to undergo this test. Gallstones cause most cases, leading to a blockage in the gallbladder duct. The rest are due to bile stasis, which is when bile can’t flow normally and leads to inflammation. Bile stasis primarily occurs in the very old, the very young, those who are critically ill (like trauma, burn, and patients with compromised immune systems), and patients on total parenteral nutrition (a feeding method).
Remember, hepatobiliary scintigraphy is a helpful tool to differentiate between biliary atresia and severe neonatal hepatitis, which can both cause jaundice in newborns.
When a Person Should Avoid Hepatobiliary Scintigraphy
There are very few and exceptional cases when the radioactive tracer used for medical tests can’t be tolerated by a patient. The only definite restriction is if the individual had a severe allergic reaction, known as anaphylaxis, to this radioactive substance before.
The more common concerns lie in how well the patient prepares for the testing procedure. To do this, doctors will check if the patient has taken any certain medications before the test.
Many different drugs can influence the functioning of your gallbladder. The most common drug that affects the procedure is opioids, which are often used to manage the patient’s pain. Morphine, which belongs to the opioid family, can tighten a muscle in your bile duct known as the sphincter of Oddi. This tightening creates a blockage that can seem like a real, physical barrier, leading to a wrong diagnosis. To avoid such situations, opioids should be avoided for at least 6 hours before the test. Additionally, opioids can affect the normal functioning of the gallbladder. So, if a chronic gallbladder disease test is scheduled, opioids should not be taken to prevent misleading results.
There are also other medicines that can affect how well your gallbladder works. Before starting a chronic gallbladder disease assessment, doctors may need to weigh the pros and cons of continuing or stopping these drugs. What drugs are these? They are:
- Atropine
- Benzodiazepines
- Ethanol (Alcohol)
- Indomethacin
- Nicotine
- Nifedipine
- Oral contraceptives (birth control pills)
- Octreotide
- Theophylline
Equipment used for Hepatobiliary Scintigraphy
Technetium-99m is a type of radioactive form of technetium that can be combined with substances called iminodiacetic acid (IDA) elements and their similar forms. Today, most often, we use Technetium-99m mebrofenin. We prefer it because it gets picked up efficiently by the liver, allowing us to produce images that show the biliary system (network of tubes conducting bile from the liver into the intestines). This is particularly useful when trying to diagnose conditions that involve this system, such as acute (sudden and severe) or chronic (long-term) biliary diseases.
To capture these images, we use a machine called an HBS (hepatobiliary scintigraphy) that comes with a large field-of-view gamma camera. This camera uses a component called a low-energy all-purpose collimator to capture the images of the 140 keV photons emitted by Technetium-99m.
Who is needed to perform Hepatobiliary Scintigraphy?
According to the rules set by the Society of Nuclear Medicine for general imaging, three types of trained professionals are needed to carry out certain tasks. These tasks involve setting up the equipment, giving certain drugs that show up on scans, and looking at the results of the scan.
The first professional is a physician who has specialized training and certification in either nuclear medicine or radiology, including nuclear radiology. This means they are experts in using radioactive substances or imaging technology to diagnose and treat various conditions.
The second is a medical physicist, who is certified by either the American Board of Science in Nuclear Medicine or by the American Board of Radiology. Medical physicists are like the engineers of the medical world. They ensure that all the equipment works properly and safely.
The third professional is a nuclear technologist, who is certified by the Nuclear Medicine Technology Certification Board. Nuclear technologists prepare and administer the radioactive drugs that help create images of your body for the doctor to examine.
Preparing for Hepatobiliary Scintigraphy
Before having a hepatobiliary scintigraphy, which is a scan used to look at your liver, gallbladder, bile ducts, and small intestine, the patient’s preparation will vary depending on what the doctor is looking to find out from the scan. The preparation for checking cholecystitis (inflammation of the gallbladder) differs from prep for a biliary leak (when bile leaks from the bile ducts), and is different again for evaluation of biliary atresia (a blockage in the tubes (ducts) that carry bile from the liver to the gallbladder).
For Acute Cholecystitis:
Patients should avoid eating for 4 to 6 hours before the radioactive tracer injection used for the scan. Fatty foods can trigger the release of a body chemical that contracts the gallbladder and can affect the results of the scan. Being hungry for this period generally allows the gallbladder to relax for the best scan results. Starving for more than 24 hours can cause the bile in the gallbladder to thicken and may lead to a false positive result (a false alarm suggesting inflammation of the gallbladder). To ensure the best results, a synthetic hormone, sincalide, should be given before the scan to help empty the gallbladder. Pain relief medications, known as opiates, should be avoided for at least 6 hours if there is a concern for a blockage in the bile duct.
For Chronic Biliary Disease:
Just like with acute cholecystitis, patients should avoid eating for 4 to 6 hours before the scan, but no more than 24 hours. Pain relief medications called opiates should be suspended for at least 6 hours, as they may affect the results.
For a Biliary Leak:
No special preparations are needed for this scan, including fasting or avoiding certain medications.
For Biliary Obstruction:
As with cholecystitis scans, patients should avoid food for 4 to 6 hours before the scan, and opiates should be withheld for at least 6 hours. This is to prevent the painkillers from slowing down the flow of a kind of tagged material from the bile duct into the small intestine, which could falsely suggest a real blockage.
For Biliary Atresia:
Phenobarbital, a type of medication, helps to improve the results of the scan when used to check for biliary atresia. This medication improves the liver’s ability to handle bilirubin, a yellow pigment that is produced when the liver breaks down old red blood cells. By doing this, it helps to reduce the chance of a false positive result. The recommended dose is 5 mg per kilogram of body weight per day for five days before the scan.
How is Hepatobiliary Scintigraphy performed
During the first hour of your examination, you’ll be lying on a table with a special camera (known as a gamma camera) overhead. A substance that can be observed by the camera, also known as a radiotracer, will be introduced into your system. This allows the camera to take pictures of your internal organs from the front every minute. After an hour, the camera takes images from different angles to get a clearer view of your common bile duct, gallbladder, and an area of your gut called the duodenum. These images help the doctor understand the activity within these areas and how they move relative to each other.
After the first hour, the next steps will depend on the results of those initial images and your symptoms. There are different approaches for different situations.
If you are suspected of having a condition called acute cholecystitis (inflammation of the gallbladder), it’s the absence of the radiotracer in the gallbladder after the initial hour that raises concerns. To confirm this, more images would be taken after 3 hours or more. But sometimes, a quick diagnosis is critical. In such cases, a low dose of a medicine called morphine might be given. Morphine forces bile (digestive juice) to flow into the gallbladder. If the duct leading to your gallbladder is not blocked, we’d see the gallbladder filling within 30 minutes or so. This method allows the entire exam to be completed in about 1.5 hours. If the gallbladder is still not visible after delayed imaging or morphine administration, this confirms acute cholecystitis. If the gallbladder does fill up, then it’s an indication that this condition is absent.
When the focus is more on the liver’s function, in severe cases there might be very little excretion of the radiotracer into the bowel. In such cases, you might need delayed imaging lasting up to a day to be sure that a cystic duct is not blocked.
If the doctor is investigating chronic gallbladder disease (a long-term inflammation of the gallbladder), the fact that the gallbladder is slow to fill or doesn’t empty well after the first hour may suggest this condition. However, since most of the patients with this condition show normal gallbladder filling within the first hour, a substance called CCK will be administered to help diagnose it. The amount of bile juice ejected by the gallbladder is then measured. If the ejection is less than a certain percentage, it may suggest chronic gallbladder disease.
If you have a biliary leak (leakage from your bile duct), the substance observed by the camera would be found in areas it’s not supposed to be, like outside the liver, biliary tree, and bowel. If there is a considerable leak, this may be visible during the first hour of imaging. Delayed images may be taken up to a day later to spot any slow or small leaks.
If the radio tracer is not visible in the bowel within the first hour, it might be due to a blocked bile duct, a condition called biliary obstruction, a common occurrence in some individuals, or a result of a previous treatment with CCK. This delayed image could take up to a day. The severity of the blockage can be estimated by how much the tracer reaches the bowel. In a condition called biliary atresia (a birth defect that leads to complete biliary obstruction), it’s suggested when no radiotracer is seen in the bowel by the end of 24 hours.
Possible Complications of Hepatobiliary Scintigraphy
During a usual HeartBlood Scan (HBS), a patient is exposed to a certain amount of low-level radiation (3 to 4 mSv), which is similar to the background radiation one would naturally encounter in a year. To put it in perspective, a chest x-ray exposes you to a far smaller amount of radiation (0.001 mSv), while a head CT scan could expose you to between 1 to 5 mSv for a single scan.
What Else Should I Know About Hepatobiliary Scintigraphy?
Hepatobiliary scintigraphy is a specialized imaging test that tracks the path of bilirubin, a substance produced by the liver. This test is useful because it uses a radioactive tracer that is absorbed by liver cells, then excreted into the bile ducts and eventually into the gallbladder and first part of the small intestine, known as the duodenum. This allows doctors to accurately and effectively evaluate and diagnose diseases related to the gallbladder and bile ducts such as inflammation (cholecystitis), blockages, or leaks. Hepatobiliary scintigraphy can also somewhat assess the functioning condition of the liver, though to a lesser degree.
