Liver Ultrasound Probe Positioning and Transducer Placement for Liver Scanning (Abdominal USG)

1. Left Lobe of Liver (Transverse View)

• Place the probe in the midline under the costal margin in transverse orientation.

• Ask the patient to take a deep breath to bring the liver into view.

• Structures visualized: Left lobe, caudate lobe, and left portal vein (LPV).

2. Left Lobe of Liver (Longitudinal View)

• Rotate the probe 90° clockwise into longitudinal orientation.

• Sweep towards the left upper quadrant to visualize the splenic vein, splenic artery, and stomach.

• Identify the pancreas and edge of the left lobe.

3. Porta Hepatis and Bile Duct

• Keep the probe in longitudinal orientation and move slightly to the right.

• Identify the portal vein and its entry into the liver (porta hepatis).

• Rotate slightly anticlockwise to locate the common bile duct (CBD).

4. Right Lobe and Hepatic Veins (Transverse View)

• Place the transducer parallel and just below the right costal margin in transverse orientation.

• Ask the patient to take a deep breath to visualize hepatic veins and IVC.

• Structures visualized: Right hepatic vein (RHV), middle hepatic vein (MHV), and left hepatic vein (LHV).

5. Right Lobe Medial to Kidney (Longitudinal View)

• Move the probe further to the right of the patient.

• Sweep left and right to visualize the right lobe and its relation to the kidney.

• Structures visualized: Hepatic veins, portal veins, gallbladder.

6. Right Lobe and Hepatic Veins (Oblique Subcostal View)

• During deep inspiration, angle the probe toward the patient’s right shoulder.

• Scan under the costal margin to evaluate hepatic veins and their drainage into the IVC.

Key measurements & normal reference values

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1. Craniocaudal (CC) length

• The CC length is measured in a sagittal or oblique longitudinal plane, typically in the right lobe of the liver, often along the right mid-clavicular line (MCL). 

• One strongly referenced method: from the uppermost right hemi-diaphragm to the inferior tip of the right lobe, through a horizontal line parallel to the anterior liver wall. 

• Normal adult values: In the MCL measurement, values >15.5-16 cm are often considered enlarged. 

• Example: A study found for the adult right lobe: 13.0 ± 1.5 cm for females and 14.1 ± 1.3 cm for males. 

• Technique tip: Patient supine, take a deep inspiration (which lowers diaphragm and pulls liver down) to better visualize the dome and inferior border. Use longitudinal plane, good acoustic window. 

2. Transverse diameter (Width)

• The transverse diameter is measured in a transverse/axial plane, typically the widest span of the liver from side to side. 

• Typical normal range: ~20-23 cm in adults. 

• Technique tip: Place the probe in a transverse orientation (often subcostal or intercostal) sweeping across to capture maximum lateral extent of liver.

3. Anteroposterior (AP) (Depth) measurement

• AP measurement captures the depth/“thickness” of the liver in the anterior-posterior dimension. 

• Some studies report the AP dimension for liver in healthy adult volunteers: ~15.8 ± 1.9 cm (CI 12.6/19.8 cm) in one MRI-based study (useful benchmark though not USG). 

• In ultrasound practice, AP measurements are used less often than CC/width for routine hepatomegaly screening, but can be useful adjuncts.

4. Volume estimation

• Liver volume can be estimated using formulae derived from linear measurements. For example, in the referenced video description:

  Liver Volume (cm³) = 343.71 + [0.84 × A × B × C]
  Where:

  • A = Left lobe AP diameter

  • B = Craniocaudal length

  • C = AP measurement (Right lobe) 

• Important caveat: Correlation between simple linear dimensions and true volume isn’t perfect; one study found poor correlation (CC r = 0.393, AP r = 0.359) using MRI as reference. 

• Technique tip: Ensure consistent measurement planes, avoid oblique angulation, and use same protocol if doing serial follow-up.

Step-by-step measurement approach

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1. Patient position & preparation

   • Supine position, consider slight head-end elevation.

   • Ask deep breath hold to lower the diaphragm. 

   • Use subcostal and intercostal windows as needed (especially if rib shadowing/gas). 

2. Locate appropriate lobe and plane

   • For CC length: Move probe to right mid-clavicular line (or mid-axillary line in some studies) in longitudinal orientation. Visualise from hepatic dome (under diaphragm) to inferior tip of right lobe. 

   • For transverse diameter: Place probe transversely across liver, sweep to capture maximum lateral span.

   • For AP depth: Use image where liver appears in transverse/axial or oblique section and measure front-to-back (anterior to posterior).

3. Place measurement calipers correctly

   • Ensure measurement is along a straight line (not curved), parallel to anterior liver wall for CC. 

   • Avoid rib shadows, bowel gas. Use acoustic windows carefully.

   • Document respiratory phase — ideally during breath hold.

4. Record values & compare to reference ranges

   • For example: CC length >15.5-16 cm may suggest hepatomegaly. 

   • Transverse ~20-23 cm typical normal in adult.

   • Keep consistent protocol if doing serial measurements.

5. Volume estimate (if required)

   • Use formula if validated in your institution. Be cautious of limitations: linear measurement approximations may not reflect actual volume accurately. 

   • Document method used for volume calculation (e.g., “Liver volume estimated via [method]”).

Pitfalls & practical tips

• The full inferior tip of the right lobe may be difficult to visualise (rib shadowing, patient habitus) — thus measurement may be underestimated. 

• Body habitus (obesity, large waist circumference) can influence liver size and measurement accuracy. 

• Different operators/machines might get slightly different values — hence intra- and inter-observer consistency matters. 

• Ensure measurement plane is reproducible for follow-up studies.

• Be aware of anatomical variants like a Riedel’s lobe (which may increase apparent size without pathology).