HIDA scans are diagnostic imaging procedures used to evaluate the liver, gallbladder, and bile ducts. This article provides a clear understanding of HIDA scans, addressing common concerns regarding radiation exposure, potential reactions, and specific situations requiring caution.
Understanding HIDA Scans
A HIDA scan, also known as hepatobiliary iminodiacetic acid scan or cholescintigraphy, is an imaging test that assesses the function of your liver, bile ducts, and gallbladder. The procedure involves injecting a small amount of a radioactive tracer, typically technetium-99m, into a vein in your arm. This tracer is absorbed by the liver, then travels with bile into the bile ducts, the gallbladder for storage, and finally into the small intestine.
A specialized camera, called a gamma camera, tracks the movement of the tracer through your biliary system, capturing images that highlight its path. These images help healthcare providers diagnose conditions such as acute or chronic gallbladder inflammation (cholecystitis), blockages in the bile ducts, bile leaks, or other issues affecting liver function. In some cases, a medication like cholecystokinin (CCK) may be administered during the scan to stimulate the gallbladder and evaluate its ability to contract and release bile.
Radiation Exposure and Safety
The primary concern for many patients undergoing a HIDA scan is radiation exposure. The radioactive tracer, Technetium-99m, emits a small amount of ionizing radiation. The typical effective radiation dose from a HIDA scan is approximately 2.5 millisieverts (mSv). This dose is considered low, comparable to the natural background radiation an average person receives in a year or the radiation from a head CT scan.
Technetium-99m has a relatively short physical half-life of about 6 hours, meaning half of its radioactivity decays every six hours, ensuring it rapidly loses its radioactive properties. The body also quickly eliminates the tracer, further minimizing prolonged exposure. Medical professionals adhere to the principle of “as low as reasonably achievable” (ALARA), employing the lowest possible amount of radioactive material to obtain diagnostic images while minimizing patient exposure.
Potential Considerations and Reactions
Beyond radiation exposure, other potential considerations and reactions associated with HIDA scans are generally minor and rare. Some individuals may experience slight discomfort or bruising at the injection site. These localized effects are usually temporary and resolve quickly.
Allergic reactions to the radiopharmaceutical itself are very uncommon. If cholecystokinin (CCK) is given to stimulate gallbladder contraction, it might cause mild abdominal cramping or nausea, which typically subsides shortly after administration. Any pain experienced during the scan is often due to the underlying condition being investigated, such as gallbladder inflammation, rather than the procedure itself.
Situations Requiring Special Caution
Certain patient populations or conditions necessitate extra consideration before undergoing a HIDA scan. Pregnancy is a primary concern, and HIDA scans are generally avoided in pregnant individuals due to potential harm to the developing fetus from radiation exposure. Inform your healthcare provider immediately if there is any possibility of pregnancy.
For breastfeeding individuals, the radioactive tracer can pass into breast milk. To prevent infant exposure, healthcare providers typically recommend temporarily interrupting breastfeeding for a period, usually 1 to 3 days, following the scan. During this time, mothers may need to pump and discard their milk or use previously stored milk or formula. Additionally, individuals with severe liver disease or known allergies to any components of the radiotracer or other medications used during the scan should discuss these concerns with their doctor.