Hepatobiliary iminodiacetic acid

Hepatobiliary Iminodiacetic Acid

Hepatobiliary iminodiacetic acid (HIDA) is a radiopharmaceutical agent used in nuclear medicine imaging to evaluate the function of the liver, gallbladder, and bile ducts. It is particularly useful in diagnosing conditions such as acute cholecystitis, bile duct obstruction, and congenital abnormalities of the biliary system.

Chemical Composition and Mechanism

HIDA is a derivative of iminodiacetic acid, which is a chelating agent. When labeled with the radioactive isotope technetium-99m (Tc-99m), it forms Tc-99m HIDA, which is the active compound used in imaging. The chemical structure allows it to be taken up by hepatocytes and excreted into the bile, following the natural pathway of bile excretion.

Clinical Applications

Diagnostic Imaging

Tc-99m HIDA scans, also known as hepatobiliary scintigraphy or cholescintigraphy, are used to assess the function of the liver and biliary system. The procedure involves intravenous injection of the radiotracer, followed by imaging with a gamma camera. The distribution and flow of the tracer are monitored to evaluate:

• Liver Function: The uptake of HIDA by the liver can indicate hepatocyte function.
• Gallbladder Function: Non-visualization of the gallbladder may suggest acute cholecystitis.
• Biliary Obstruction: Delayed or absent tracer flow into the intestines can indicate bile duct obstruction.

Acute Cholecystitis

In cases of suspected acute cholecystitis, a HIDA scan can confirm the diagnosis by demonstrating non-visualization of the gallbladder due to cystic duct obstruction.

Biliary Atresia

In neonates with jaundice, a HIDA scan can help differentiate biliary atresia from other causes of neonatal jaundice by assessing bile flow into the intestines.

Procedure

The patient is injected with Tc-99m HIDA intravenously. Imaging begins shortly after injection and continues for about 1-2 hours. The patient may be given a fatty meal or a cholecystokinin analog to stimulate gallbladder contraction and assess its function.

Safety and Side Effects

HIDA scans are generally safe, with minimal radiation exposure. Side effects are rare but may include allergic reactions to the radiotracer. The procedure is contraindicated in pregnant women due to radiation exposure.

Also see

• Cholecystitis
• Biliary Atresia
• Nuclear Medicine
• Radiopharmaceutical