What is the protocol for a liver ultrasound scan?

Liver Ultrasound Scanning Protocol

For routine liver ultrasound examination, patients should fast for a minimum of 3 hours prior to the procedure, though recent evidence suggests fasting may not be strictly necessary for adequate image quality in most cases. 1

Pre-Procedure Preparation

Patient Fasting Requirements

• A minimum 3-hour fasting period is recommended when performing liver stiffness measurements or elastography, as meal ingestion increases liver stiffness values and can lead to overestimation of fibrosis 1
• For standard B-mode ultrasound imaging alone, prolonged fasting may not significantly improve image quality, and unnecessary fasting should be avoided to prevent patient distress and hypoglycemia 2
• No specific preparation is required for basic abdominal or liver ultrasound beyond the fasting consideration 1

Pre-Scan Imaging Review

• Recent liver imaging (within 3 months) should be reviewed before any procedure to identify anatomical variations, focal lesions, or contraindications 1
• This review helps determine the optimal scanning approach and identifies any structures requiring targeted evaluation 1

Standard Scanning Protocol

Technical Approach

• Ultrasound is the primary screening modality for liver assessment due to its wide availability, lack of ionizing radiation, cost-effectiveness, and ability to be performed without sedation 1
• The examination should evaluate multiple parameters systematically rather than relying on parenchymal echo alone, as this improves diagnostic accuracy 3

Key Anatomical Structures to Assess

The following structures should be systematically evaluated and documented 2:

• Liver parenchyma (echogenicity, texture, focal lesions)
• Gallbladder
• Common hepatic duct (proximal common duct)
• Common bile duct (distal common duct)
• Pancreatic head, body, and tail
• Origin of the superior mesenteric artery
• Portal vein and hepatic veins

Specific Liver Parenchymal Assessment

When evaluating for diffuse liver disease, document 4, 5:

• Hepatomegaly or size changes
• Parenchymal echogenicity (increased echogenicity reliably indicates fatty infiltration)
• Liver surface contour (nodularity suggests cirrhosis)
• Right lobe to caudate lobe ratio (decreased ratio indicates cirrhosis)
• Indirect signs of portal hypertension (collateral vessels, splenomegaly)

Fatty Liver Grading

Use a 5-parameter scoring system rather than parenchymal echo alone, as this significantly improves diagnostic performance (AUROC 0.89 vs 0.82) 3:

• Parenchymal brightness/echogenicity
• Liver-to-kidney contrast
• Deep beam attenuation
• Vessel wall clarity
• Hepatic vein visualization

Important caveat: Ultrasound sensitivity is significantly reduced when liver fat content is below 12.5%, and it cannot reliably distinguish between adjacent grades of steatosis 3

Surveillance Protocols for High-Risk Patients

Hepatocellular Carcinoma Screening

For patients with cirrhosis or chronic hepatitis B with risk factors 6:

• Perform ultrasound examination every 6 months as the standard surveillance interval
• Consider combining ultrasound with alpha-fetoprotein (AFP) testing to increase sensitivity, though this decreases specificity 6
• For nodules ≥1 cm detected on screening, proceed to multiphasic contrast-enhanced CT or MRI for characterization 6

Image-Guided vs. Unguided Scanning

• Ultrasound assistance or guidance should be used whenever possible to minimize complications and improve diagnostic yield, particularly when targeting focal lesions 1
• Real-time ultrasound guidance is mandatory for biopsy of focal liver lesions to ensure accurate needle placement 1
• Ultrasound assistance can change the chosen biopsy site in up to 15% of cases to avoid adjacent structures 1

Advanced Techniques

Elastography Integration

When assessing for fibrosis or cirrhosis, consider adding 1:

• Vibration-controlled transient elastography (TE) - most widely validated method
• Point shear wave elastography (pSWE) or 2D shear wave elastography (2D-SWE) - integrated into ultrasound devices
• Acoustic radiation force impulse (ARFI) - useful in patients with obesity, ascites, or NAFLD 1

Critical limitation: Elastography results can overestimate fibrosis in the presence of inflammation, obstructive cholestasis, recent food ingestion, exercise, or venous congestion - these must be excluded before interpretation 1

Contrast-Enhanced Ultrasound

• Emerging technique using gas-filled microbubbles for lesion characterization 1
• Requires IV access but no sedation 1
• May be useful in patients with advanced chronic liver disease 1

Common Pitfalls to Avoid

• Do not perform ultrasound within 3 hours of meal ingestion if elastography or stiffness measurement is planned, as this causes falsely elevated values 1
• Do not rely solely on parenchymal echogenicity for fatty liver diagnosis; use multiple ultrasonographic parameters 3
• Recognize that ultrasound has limited sensitivity for detecting steatosis below 12.5% liver fat content and cannot adequately discriminate between adjacent fibrosis stages 1, 3
• Ultrasound is of limited usefulness in acute hepatitis and should not be the primary diagnostic tool in this setting 4
• Image quality may be suboptimal in morbidly obese patients, those with significant ascites, or nodular cirrhotic livers - consider alternative imaging (CT or MRI) in these cases 1