A HIDA scan is most often done to evaluate your gallbladder. It's also used to look at the bile-excreting function of your liver and to track the flow of bile from your liver into your small intestine. A HIDA scan images liver function, which complements images of body structure (anatomy) provided by X-ray and ultrasound.
A HIDA scan may help in the diagnosis of several diseases and conditions, such as:
- Gallbladder inflammation (cholecystitis)
- Bile duct obstruction
- Congenital abnormalities in the bile ducts, such as biliary atresia
- Postoperative complications, such as bile leaks and fistulas
- Assessment of liver transplant
Your doctor may use a HIDA scan as part of a test to measure the rate at which bile is released from your gallbladder (gallbladder ejection fraction).
A HIDA scan carries few risks. Risks may include:
- Allergic reaction to medications containing radioactive tracers used for the scan
- Bruising at the injection site
Tell your doctor if there's a chance you could be pregnant or if you're breast-feeding. In most cases nuclear medicine tests, such as the HIDA scan, aren't performed in pregnant women because of potential harm to the fetus.
Risks of radiation
The amount of radioactive tracer injected into your arm during a HIDA scan is very small. The radioactive tracer gives off radiation for several hours and then becomes inactive. The gamma camera that takes images of your liver, gallbladder, bile duct and small intestine during a HIDA scan doesn't give off any radiation. If you're concerned about the amount of radiation you'll be exposed to during a HIDA scan, talk with your doctor.
To prepare for your HIDA scan, your doctor may ask you to:
- Fast for a few hours. Expect to fast for a minimum of four hours before your HIDA scan. You may be allowed to drink clear liquids.
- Delay taking some medications. Certain medications may interfere with your HIDA scan, so your doctor may ask that you delay taking your medications on the day of your scan. Tell your doctor about any medications you're taking.
- Take medications that enhance the scan. Certain medications may make it easier for the nuclear radiologist to interpret the results of your HIDA scan. Whether you will need these medications depends on the reason for your scan. In some cases you may receive an infusion or injection of a medication in addition to the injected radioactive tracer. The medications may be injected immediately before or during your HIDA scan. In rare instances you may be asked to start taking a medication a few days before your scan.
You'll be asked to change into a hospital gown before your HIDA scan begins. Your health care team will position you on a table, usually on your back. The radioactive tracer is then injected into a vein in your arm.
The tracer travels through your bloodstream to your liver, where it's taken up by the bile-producing cells. The radioactive tracer travels with the bile from your liver into your gallbladder and through your bile ducts to your small intestine.
You may feel some pressure while the radioactive tracer is injected into your vein.
As you lie on the table, a special gamma camera is positioned over your abdomen taking pictures of the tracer as it moves through your body. The gamma camera takes pictures continually for about an hour.
You'll need to keep still during the HIDA scan. This can become uncomfortable, but you may find that you can lessen the discomfort by taking deep breaths and thinking about other things. Tell your health care team if you're uncomfortable.
The radiologist will watch on a computer the progress of the radioactive tracer through your body. The HIDA scan may be stopped when the radioactive tracer is seen in the gallbladder and enters your small intestine. This typically takes about an hour. In some cases extra imaging will be performed if original images aren't satisfactory, if morphine is given to help visualize the gallbladder or if the medication CCK is given to look at the contraction of the gallbladder.
After your HIDA scan
In most cases you can go about your day after your HIDA scan. You'll likely still have some of the radioactive tracer in your body. The substance will leave your body by natural decay or through your urine over the next day or two.
In most cases, the doctor who interprets the HIDA scan images (nuclear radiologist) will send the results to your doctor, who will discuss them with you.
In HIDA scan images viewed on a computer monitor, the radiotracer appears as regions of dark color on a lighter background. The more dark color in a given area, the greater the amount of radioactive tracer present. The movement of this dark color throughout the series of HIDA scan images indicates that the radioactive tracer was able to move freely through your liver, bile ducts and gallbladder and into the small intestine. If the radioactive tracer is missing from certain areas on a scan, it may indicate a blockage or other problem.
HIDA scans on their own usually can't diagnose a problem. Your doctor considers them along with your signs and symptoms, other test results, and other imaging to arrive at a diagnosis.
Results of a HIDA scan include:
- Normal. A normal result means that the radioactive tracer moved freely along with the bile from your liver into your gallbladder and small intestine. No problems were detected.
- Slow movement of radioactive tracer. If the radioactive tracer moves through your bile ducts very slowly, this may indicate a blockage or obstruction, or a problem in liver function.
- No radioactive tracer seen in the gallbladder. If the radioactive tracer isn't seen in your gallbladder, this may indicate acute inflammation (acute cholecystitis).
- Abnormal low gallbladder ejection fraction. If the amount of radiotracer leaving the gallbladder is low after giving the medication CCK, this may indicate chronic inflammation (chronic cholecystitis).
- Radioactive tracer detected in other areas. If the radioactive tracer is found outside of your biliary system, this may indicate a leak.
Your doctor will discuss your specific results with you.