What is the liver protocol during Computed Tomography (CT)?

Liver Protocol for CT Imaging

The standard liver protocol for CT imaging should include a multiphasic approach with arterial, portal venous, and delayed phases to optimize detection and characterization of liver lesions. 1

Essential Components of Liver CT Protocol

Contrast Administration

• Use intravenous contrast with an injection rate of 4-5 mL/sec for optimal arterial phase imaging 1
• Employ weight-based contrast dosing (approximately 1.7 mL/kg) rather than fixed dosing to improve liver enhancement 2
• Fixed injection duration is critical for precise estimation of scan timing for each phase 3

Imaging Phases

• Non-contrast phase: Optional but recommended for patients with prior liver-directed therapy or when hemorrhage/calcification is suspected 1
• Arterial phase: Critical for detection of hypervascular lesions and lesion characterization 1
  • Optimal timing: 20-25 seconds after contrast trigger when using 4 mL/sec injection rate 4
• Portal venous phase: Essential for detection of hypovascular metastases 1
  • Typically acquired 60-70 seconds after contrast injection 1
• Delayed phase (3-5 minutes): Improves lesion characterization 1

Technical Parameters

• Slice thickness: 2.5-5 mm (thinner slices improve lesion detection) 1
• kVp: 120-150 1
• mA: 80-300 1
• Consider bolus-tracking technology to optimize scan timing 5

Protocol Variations Based on Clinical Context

For Suspected Hepatocellular Carcinoma (HCC)

• Multiphasic imaging is essential as HCC typically shows arterial hypervascularity and "washout" on portal venous phases 1
• Include all phases (non-contrast, arterial, portal venous, delayed) for patients who have received liver-directed therapy 1
• Consider dual-energy CT to create virtual unenhanced images and reduce radiation dose 1

For Suspected Metastases

• For hypovascular metastases (most common type): Portal venous phase is most sensitive (85-91.5% sensitivity) 1
• For hypervascular metastases (from neuroendocrine tumors, renal cell carcinoma, thyroid carcinoma, melanoma):
  • Arterial phase is critical as these lesions may be missed if only portal venous phase is performed 1
  • Multiphase imaging required as up to 59% of these metastases may be isodense on either arterial or portal venous phases 1

For Post-Treatment Surveillance

• Include non-contrast phase for patients who have received liver-directed therapy 1
• First follow-up imaging at 1 month post-treatment, followed by imaging every 3 months 1

Common Pitfalls and Considerations

• Inadequate contrast injection rate (<4 mL/sec) may result in suboptimal arterial phase imaging 1
• Insufficient contrast dose in larger patients leads to poor liver enhancement 2
• Improper timing of arterial phase can miss hypervascular lesions 4
• Recent research suggests that a three-phase protocol (excluding non-contrast phase) may be adequate for HCC diagnosis when combined with advanced image analysis, potentially reducing radiation exposure 6

Special Considerations

• For patients with renal insufficiency, consider alternative imaging modalities such as MRI 1
• For obese patients, adjust technical parameters and contrast dose to maintain image quality 2
• Real-time bolus tracking significantly increases mean hepatic enhancement and improves portal venous hepatic CT scanning 5