Hepatobiliary Imaging Overview

Hepatobiliary Imaging

• Biliary Tract Components: Canaliculi, right and left hepatic ducts, common hepatic duct, cystic duct, common bile duct, and sphincter of Oddi.
• Bile Flow: Bile flows from canaliculi to hepatic ducts, then common hepatic duct, and finally to the duodenum via the sphincter of Oddi.
• Gallbladder Function: Stores bile when the sphincter of Oddi is contracted and releases it into the duodenum for digestion.
• Bile Function: Emulsifies fats, promotes peristalsis, and aids in fatty acid absorption.
• Bile Production: Bile is produced by erythrocyte breakdown and hepatocyte metabolism.
• Bile Secretion Stimulation: Cholecystokinin (CCK) stimulates gallbladder bile release when fatty foods enter the duodenum.

Clinical Indications

• Upper Abdominal Pain: Hepatobiliary imaging helps rule out cystic duct obstruction (acute cholecystitis) in patients with upper abdominal pain.
• Jaundice: Imaging differentiates between causes of jaundice, including biliary tract obstruction.
• Post-Surgical Evaluation: Images assess bile drainage and reflux following surgical procedures.
• Cold Defects (Tc99m-sulfur colloid): May indicate normal or abnormal variants in the biliary system.
• Pediatric Applications: Detects choledochal cysts, biliary atresia, and other congenital biliary tree anomalies.

Radiopharmaceuticals

• Agents: Mebrofenin, disofenin, lidofenin (Tc-labeled iminodiacetic acids).
• Drug Distribution: Compounds are extracted from the blood by hepatocytes and transported into canaliculi with bile.
• Bile Flow Tracking: IDA compounds follow bile flow, visualizing the biliary system.
• Factors Affecting Uptake: IDA compound structure, hepatic blood flow, hepatocyte health, and bilirubin level.
• Bilirubin Effects: High bilirubin levels reduce tracer uptake, potentially requiring higher dosages.
• Dosage: Adult dosage of 99mTc-IDA varies from 2 to 8 mCi, adjusted for serum bilirubin.

Patient Preparation

• Cystic Duct Obstruction: Bile flow into the gallbladder rules out cystic duct obstruction.
• Medication Discontinuation: Narcotics, sedatives, and drugs that relax the sphincter of Oddi should be stopped before imaging.
• Morphine Effects: Opiates increase sphincter tone, promoting gallbladder filling.
• Fasting: 2–4 hours before, but not exceeding 24 hours, to prevent gallbladder emptying of tracer.
• Fasting Rationale: Prevents tracer emptying after a fatty meal.

Imaging Procedure

• Procedure Start: Imaging begins after tracer injection using a scintillation camera with a low-energy collimator.
• Patient Position: Supine position for simultaneous liver, biliary tract, and small intestine imaging.
• Image Acquisition: Sequential 5-minute images over 45–60 minutes.
• Initial Projections: Anterior oblique or right lateral views after the first hour for bowel assessment.
• Delayed Imaging: Obtain views up to 24 hours if gallbladder or bile ducts aren't initially visualized.
• Delayed Small Intestine Views: Acquire if gallbladder and common bile duct are visualized but no tracer in the small intestine.

Sincalide (Kinevac)

• Usage: Empties the gallbladder before injecting the radioactive tracer.
• Administration: 0.01–0.02 g/kg intravenously over 3–5 minutes, 30–60 minutes before injection.
• Indications: Prolonged fasting, hyperalimentation.
• Administration Timing: Typically given 60 minutes after tracer to visualize the gallbladder and calculate GBEF.
• Effect on Gallbladder: Empties the gallbladder; administered before and after tracer for GBEF calculation.
• Morphine Interaction: Avoid administering after morphine to avoid potential interference and inaccurate GBEF.
• Gallbladder Emptying Time: Typically begins 2 minutes after, lasting approximately 11 minutes.
• Acquisition: 30-minute image acquisition at 1-2 frames/minute after infusion.
• Normal GBEF: Generally 35% or greater; less than 35% may suggest acute acalculous cholecystitis.
• Contraindications: Hypersensitivity, intestinal obstruction.
• Side Effects: Nausea, abdominal pain, urge to defecate, dizziness, flushing.

Morphine Sulfate (Astranorph, Duramorph)

• Administration: Intravenously if gallbladder isn't visualized within 40–60 minutes after tracer.
• Effect: Contracts sphincter of Oddi, increasing bile duct pressure, forcing tracer into the gallbladder.
• Nonvisualization After Morphine: Increased likelihood of acute cholecystitis.
• Dose: 0.04–0.1 mg/kg intravenously over 2–3 minutes.
• Imaging Duration: Continued for approximately 30 minutes post-injection.
• Contraindications: Premature infants, respiratory distress, morphine allergy, acute pancreatitis.

Phenobarbital (Luminal)

• Use: Differentiates biliary atresia from other neonatal jaundice causes.
• Administration: Pretreatment at 5 mg/kg/day for 3–5 days before imaging.
• Interpretation: Tracer excretion into the bowel within 24 hours suggests non-obstructive jaundice; otherwise, it suggests biliary atresia.
• Contraindications: Patient allergies or respiratory depression.
• Adverse Effects: Respiratory depression, drowsiness, hyper-excitability in children, rash, nausea, vomiting.

Image Findings

• Tracer Uptake Times: Hepatocytes (minutes), hepatic ducts/gallbladder (15–30 minutes), gallbladder (45–60 minutes), small intestine (30 minutes).
• Low GBEF (<35%): Possible acute acalculous cholecystitis.
• Nonvisualization of Gallbladder: Indicates cystic duct obstruction (acute cholecystitis).
• Delayed Gallbladder Visualization: Possible chronic cholecystitis.
• Small Intestine Issues: May indicate common bile duct obstruction.
• Bile Outside the System: Possible bile leak.

Technical Considerations

• Prolonged Fasting: Thick, viscous bile can lead to gallbladder non-visualization.
• Elevated Bilirubin: Increased bilirubin delays hepatocyte tracer clearance, possibly requiring identification on lateral/oblique views due to kidney excretion.