Influence of heterogeneities on liver steatosis evaluation by Fibroscan® (CAP™): relevance of a liver guidance tool

Purpose: Controlled Attenuation Parameter (CAP) is a measure of ultrasound attenuation developed to assess steatosis on the Fibroscan®. CAP performance in clinical studies always showed satisfactory results. However, CAP is based on the hypothesis that liver parenchyma is homogeneous whereas it is not everywhere (blood vessel, nodules, etc.). The objective of here is to determine the influence of heterogeneities on CAP and show the clinical relevance of a liver guidance tool, developed to target the homogeneous parenchyma.

Material and methods: Influence of heterogeneities was assessed on:

Field II simulations: overall attenuation varied from 100 up to 350 dB/m at 3.5 MHz. Hypo or hyper echogenic (+/- 3.6 and 12 dB) heterogeneities were embedded (size: 2 – 10 mm) at depth from 25 – 65 mm so as to cover heterogeneities usually observed in liver parenchyma;

Tissue mimicking phantoms: acquisitions were performed in the homogeneous and heterogeneous parts of two phantoms: the model G403GS (Gammex), a custom-made ultrasound phantom (ATS) with hyper and hypo echogenic inclusions with different sizes at different depths;

Clinical data: 30 patients from 3 steatosic groups (no/moderate/massive steatosis) were assessed using the Fibroscan®. Each acquisition zone was tagged as homogenenous/heterogeneous by two expert operators.

For each acquisition, CAP and the liver guidance tool were assessed.

Results: Preliminary results show that the size, amount and characteristics of heterogeneities influence CAP (cf. Fig 1). Relative difference can be up to 50% in phantoms which may induce false diagnosis.

Conclusion: The liver guidance tool allows the detection of homogenous parenchyma zone and its use in clinical practice is promising to enhance liver steatosis evaluation using Fibroscan®.