Special Report: Standardizing Pulse-Echo Quantitative Ultrasound Biomarkers for Liver Steatosis
Key findings
- There is an important unmet need for a widely available, cost-effective test to quantify liver steatosis
- Some manufacturers of ultrasound scanners have implemented pulse-echo quantitative ultrasound (PEQUS) technology, which is based on quantifying acoustic properties of tissue in a system-independent manner
- To facilitate the translation of these biomarkers into clinical practice, healthcare professionals, scientists, and industry and government representatives are collaborating on standardizing the measurement, reporting, and testing of PEQUS biomarkers
Because of the increasing incidence of nonalcoholic fatty liver disease and the emergence of liver fat–reducing therapies, radiologists urgently need a practical way to quantify liver steatosis. The ideal biomarker would be noninvasive, widely available, and cost-effective and could be safely applied serially for disease monitoring.
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A public–private partnership facilitated by the Radiological Society of North America (RSNA) is developing standards for quantitative biomarkers for measuring liver steatosis. Anthony E. Samir, MD, MPH, chief of Ultrasound Imaging Services and director of the Center for Ultrasound Research & Translation at Massachusetts General Hospital, and assistant professor of Radiology at Harvard Medical School, served as the senior author of the group's recent report in Radiology.
Limitations of Qualitative Biomarkers
Transabdominal B-mode ultrasound is useful for distinguishing moderate-to-severe steatosis from normal liver, but it's insensitive to mild steatosis. In addition, the subjective assessment of brightness contrast is influenced by the manufacturer, transducer, frequency, waveform characteristics, and operator experience.
The hepatorenal index, a semiquantitative method for evaluating steatosis, assumes a normal renal cortex and may be inaccurate in patients with kidney disease. The hepatorenal index is also of limited use in differentiating between mild and no steatosis, and there is no consensus on cutoff values.
Moreover, all these techniques are subject to confounding by fibrosis, glycogen, and infiltrative processes.
PEQUS Biomarkers
To overcome these limitations, some manufacturers of ultrasound scanners have implemented pulse-echo quantitative ultrasound (PEQUS) technology. PEQUS is based on quantifying the acoustic properties of tissue: the attenuation coefficient, backscatter coefficient, and speed of sound.
The report explains the technical principles of quantifying each of these biomarkers and describes the challenges to their implementation. At this time, there are insufficient data to recommend one PEQUS biomarker or method of implementation over another.
Harmonization Efforts
Considering the large number of ultrasound vendors offering liver fat quantification systems, there's substantial opportunity for divergence in methods.
In 2020 the Quantitative Imaging Biomarkers Alliance of the RSNA joined with the American Institute of Ultrasound in Medicine, a multidisciplinary association, to create a PEQUS Biomarker Committee. The committee represents the interests of multiple stakeholders, including clinicians, academics, government experts, and industry partners.
To reach consensus on how to measure, report, and test PEQUS biomarkers, the committee plans a prospective, multisite study of liver-mimicking phantoms. The study will include 10 ultrasound system vendors who have implemented PEQUS features, as well as 24 clinical, academic and government institutions in North and South America, Europe and Asia.
Each vendor will specify a scanner to be tested by at least three sites. The goals are to assess the intraoperator and interoperator variability of the three biomarkers, and the intersite and intervendor reproducibility.
The committee also expects to work toward standardizing other features on ultrasound systems (e.g., quality metrics, color maps, and reporting metrics) to reduce user confusion and improve the adoption of PEQUS biomarkers.
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