RSNA QIBA ultrasound shear wave speed Phase II phantom study in viscoelastic media

Abstract

Using ultrasonic shear wave speed (SWS) estimates has become popular to noninvasively evaluate liver fibrosis, but significant inter-system variability in liver SWS measurements can preclude meaningful comparison of measurements performed with different systems. The RSNA Quantitative Imaging Biomarker Alliance (QIBA) ultrasound SWS committee has been developing elastic and viscoelastic (VE) phantoms to evaluate system dependencies of SWS estimates. The objective of this study is to compare SWS measurements between commercially-available systems using phantoms that have viscoelastic properties similar to those observed in normal and fibrotic liver. CIRS, Inc. fabricated three phantoms using a proprietary oil-water emulsion infused in a Zerdine R hydrogel that were matched in viscoelastic behavior to healthy and fibrotic human liver data. Phantoms were measured at academic, clinical, government and vendor sites using different systems with curvilinear arrays at multiple focal depths (3.0, 4.5 & 7.0 cm). The results of this study show that current-generation ultrasound SWS measurement systems are able to differentiate viscoelastic materials that span healthy to fibrotic liver. The deepest focal depth (7.0 cm) yielded the greatest inter-system variability for each phantom (maximum of 17.7%) as evaluated by IQR. Inter-system variability was consistent across all 3 phantoms and was not a function of stiffness. Median SWS estimates for the greatest outlier system for each phantom/focal depth combination ranged from 12.7-17.6%. Future efforts will include performing more robust statistical analyses of these data, comparing these phantom data trends with viscoelastic digital phantom data, providing vendors with study site data to refine their systems to have more consistent measurements, and integrating these data into the QIBA ultrasound shear wave speed measurement profile.

Evaluation of Inter-System Variability in Liver Stiffness Measurements

“…Previous elastic phantom studies demonstrated inter-system variability ranging from 6 -12 % in elastic phantoms with a nominal SWS of 1.0 and 2.0 m/s [7]. In visco-elastic phantoms that more accurately simulate the liver, the median SWS estimates for the greatest outliers in each phantom/focal depth combination ranged from 12.7 -17.6 % [8].…”

Shear Wave Speed Measurements Using Crawling Wave Sonoelastography and Single Tracking Location Shear Wave Elasticity Imaging for Tissue Characterization

“…Their results suggest a bias in elastic property estimation which varies with each quantitative modality and highlights the difficulty in finding a reference method to assess the elastic properties. In [13] and [14], inter-laboratory studies of SWS estimation were performed in elastic and viscoelastic phantoms, respectively. These studies found a significant difference among measurements at different depths.…”

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“…Working on elastic phantoms, a statistically significant difference in the SWS estimates among systems and depth of measurement in the phantom was shown, whereas no statistically significant differences were found among operators using the same or equivalent systems under the same conditions [129]. Similar results were obtained using phantoms with viscoelastic properties similar to those observed in normal and fibrotic liver [130]. The measurements were performed at multiple focal depths (3.0, 4.5 and 7.0 cm).…”