How is cholescintigraphy (hepatobiliary imaging) performed? What is a normal study?
The technique for a basic cholescintigraphic study is the same for nearly all of its clinical indications. The patient is injected with a technetium-99m–labeled iminodiacetic acid (IDA) derivative. Although commonly referred to as a HIDA scan, hepatic IDA is no longer used in imaging. Disofenin and mebrofenin are used currently because of improved pharmacokinetics. High bilirubin levels (greater than 5 mg/dL for disofenin and greater than 10 mg/dL for mebrofenin) can cause a competitive inhibition of radiopharmaceutical uptake; however, administering a higher dose can overcome this impediment.
After injection, sequential images, usually 1 minute in duration, are routinely obtained for 60 minutes. Normally, the liver rapidly clears the radiopharmaceutical. On images displayed at normal intensity, blood pool activity in the heart is faint or indiscernible by 5 minutes after injection. Persistent blood pool activity and poor liver uptake are indications of hepatocellular dysfunction. Right and left hepatic ducts, the common bile duct, and small bowel are typically visualized within 30 minutes. The gallbladder usually is seen within 30 minutes but can still be considered normal if visualized within 1 hour, provided the patient has not eaten within 4 hours. By 1 hour, nearly all the activity is in the bile ducts, gallbladder, and bowel; the liver is seen faintly or not at all. In all of the studies listed in Question 3, failure to see an expected structure at 1 hour (e.g., gallbladder in acute cholecystitis, small bowel in biliary atresia) requires delayed imaging (4 hours for evaluation for acute cholecystitis, 24 hours for biliary atresia). In some cases, various manipulations, such as sincalide infusion or morphine injection, are performed after the initial 60-minute images.