Determining the ideal measurement site and respiratory condition for liver transient elastography: toward clinical practice standardization

Objectives: Liver transient elastography (TE) has been endorsed by the WHO as the first-line diagnostic tool for liver diseases. Although unreliable and invalid results caused by intercostal space (ICS)-associated factors (including excessive subcutaneous fat and a narrow ICS relative to the transducer size) and operator inexperience are not uncommon, no standard guidelines for ideal probe placement are currently available. Herein, we conducted a prospective observational study to identify an ideal measurement site and respiratory condition for TE by characterizing anatomical and biomechanical properties of the ICSs using ultrasound B-mode and elasticity imaging.

Methods: Intercostal ultrasound was performed pointwise at four specific sites in 59 patients to simultaneously measure the width, stiffness, and skin‒liver capsule distance (SCD) of the ICSs over the liver, under end-inspiratory and end-expiratory conditions. Intersections between the 8th ICS and anterior axillary line, the 7th ICS and anterior axillary line, the 8th ICS and mid-axillary line, and the 7th ICS and mid-axillary line were defined as Sites 1 to 4, respectively.

Results: Results indicated that Sites 2 and 3 presented greater intercostal width; Sites 3 and 4 displayed lower intercostal stiffness; Sites 2 and 3 exhibited a shorter SCD. The ICSs were significantly wider and stiffer at end-inspiration. Additionally, the liver was more easily visualized at Sites 1 and 3.

Conclusion: We recommend Site 3 for TE probe placement owing to its greater width, lower stiffness, and smaller abdominal wall thickness. Performing TE at end-inspiration is preferred to minimize transducer-rib interferences. This study paves the way toward a standardized TE examination procedure.

Critical relevance statement: A standardized measurement protocol for WHO-recommended liver TE was first established to improve the success and efficiency of the examination procedure.

Key points: WHO-recommended TE is unreliable or fails due to intercostal space-related factors. The 8th intercostal space on the mid-axillary line and end-inspiration are recommended. This standardized protocol aids in handling challenging cases and simplifies operational procedures.