What are the steps to perform a liver scan using ultrasound?

Liver Ultrasound Scanning: Step-by-Step Protocol

Ultrasound is the primary screening modality for liver assessment, and should follow a systematic approach beginning with patient preparation, pre-scan imaging review, and methodical evaluation of liver parenchyma, surface characteristics, and vascular structures. 1

Patient Preparation

• Ensure a minimum 3-hour fasting period before the examination, particularly if liver stiffness measurements or elastography will be performed, as meal ingestion falsely elevates liver stiffness values and leads to overestimation of fibrosis 1
• For basic liver ultrasound without elastography, no specific preparation beyond fasting is required 1
• Position the patient supine or on their left side for optimal liver visualization 2

Pre-Scan Review

• Review any recent liver imaging obtained within the preceding 3 months to identify anatomical variations (such as Chilaiditi syndrome where bowel lies between liver and abdominal wall), focal lesions, or contraindications to the procedure 2, 1
• This review determines the optimal scanning approach and identifies structures requiring targeted evaluation 1

Systematic Scanning Technique

Initial Survey

• Begin with gray-scale B-mode ultrasound as the foundation of the examination, utilizing its advantages of wide availability, lack of ionizing radiation, cost-effectiveness, and ability to perform without sedation 1, 3
• Use tissue harmonic imaging when available to improve image resolution 4

Liver Parenchyma Assessment

• Evaluate parenchymal echogenicity systematically—increased echogenicity is a reliable criterion for diagnosing fatty liver 5
• Assess liver-to-kidney contrast as part of a 5-parameter scoring system for fatty liver grading 1
• Evaluate vessel wall clarity as another parameter in the scoring system 1
• Search for hypoechoic nodules in the liver parenchyma, which may represent regenerative nodules in cirrhosis; detection of hypoechoic nodules >10mm is critical for early hepatocellular carcinoma diagnosis 6

Liver Surface and Morphology

• Examine the liver surface for nodularity, which is characteristic of cirrhosis 6, 5
• Assess the liver edge—a rounded edge suggests cirrhosis 6
• Measure and document the right lobe-to-caudate lobe ratio, as a decreased ratio indicates cirrhosis 5

Vascular Structures

• Apply color Doppler ultrasound to evaluate the portal venous system 3
• Search for portosystemic collaterals, which are beneficial for managing esophagogastric varices and portosystemic encephalopathy 6
• Document splenomegaly and ascites as indirect evidence of portal hypertension 6, 5

Additional Structures

• Systematically evaluate and document the gallbladder 1
• Assess for biliary dilatation, as bile duct obstruction can cause abnormal liver tests 5

Image-Guided Approach

• Use ultrasound guidance whenever possible to minimize complications and improve diagnostic yield, particularly when targeting focal lesions 1
• Ultrasound guidance is especially important in patients with shrunken livers where accurate needle placement on the first pass reduces bleeding risk 2

Advanced Techniques (When Indicated)

• For fibrosis assessment, vibration-controlled transient elastography (TE) is the most widely validated method 1
• Point shear wave elastography (pSWE) or 2D shear wave elastography (2D-SWE) serve as alternative methods 1
• Acoustic radiation force impulse (ARFI) is particularly useful in patients with obesity, ascites, or NAFLD 1
• Contrast-enhanced ultrasound dramatically extends diagnostic capability by improving specificity in detection and characterization of focal lesions to rival CT and MRI 4

Surveillance Protocols

• For patients with cirrhosis or chronic hepatitis B with risk factors, perform ultrasound examination every 6 months as the standard surveillance interval 1

Critical Pitfalls to Avoid

• Never perform elastography or stiffness measurements within 3 hours of meal ingestion, as this causes falsely elevated values 1
• Recognize that ultrasound has limited sensitivity for detecting steatosis below 12.5% liver fat content and cannot adequately discriminate between adjacent fibrosis stages 1
• In morbidly obese patients, those with significant ascites, or nodular cirrhotic livers where image quality is suboptimal, consider alternative imaging with CT or MRI rather than persisting with inadequate ultrasound 1
• Avoid blind procedures without recent imaging review (within 3 months) to prevent inadvertent puncture of adjacent viscera 2
• Be aware that ultrasound has relatively low overall importance for distinguishing different etiologies of diffuse liver diseases, though it remains very sensitive for detecting complications of cirrhosis 7