Abstract
ObjectiveTo investigate the accuracy and precision of ultrasound shear wave elasticity measurements as a function of target elasticity and acquisition depth.Materials and methodsUsing five ultrasound systems (VTQ, VTIQ, EPIQ 5, Aixplorer, and Aplio 500), two operators independently measured shear wave elasticities in two phantoms containing five different target elasticities (8±3, 14±4, 25±6, 45±8, and 80±12 kPa) at depths of 15, 30, 35, and 60 mm. Accuracy was assessed by evaluating measurement errors and the proportions of outliers, while factors affecting accuracy were assessed using logistic regression analysis. Measurement errors were defined as differences between the measured values and 1) the margins of the target elasticity, and 2) the median values of the target elasticity. Outliers were defined as measured values outside the margins of the target elasticity. Precision was assessed by calculating the reproducibility of measurements using the within-subject coefficient of variation (wCV).ResultsMean measurement errors and the proportions of outliers were higher for high than for low target elasticities (p<0.001), but did not differ in relation to acquisition depth, either within an elastography system or across the different systems. Logistic regression analysis showed that target elasticity (p<0.001) significantly affected accuracy, whereas acquisition depth (p>0.05) did not. The wCV for the 80±12 kPa target (31.33%) was significantly higher than that for lower elasticity targets (6.96–10.43 kPa; p<0.001). The wCV did not differ across acquisition depths. The individual elastography systems showed consistent results.ConclusionsTargets with high elasticity showed lower accuracy and lower precision than targets with low elasticity, while acquisition depth did not show consistent patterns in either accuracy or precision.
Highlights
Ultrasound (US) elastography is a noninvasive imaging modality for assessment of tissue stiffness
Logistic regression analysis showed that target elasticity (p0.05) did not
Logistic regression analysis showed that target elasticity significantly affected accuracy (p < 0.001), whereas acquisition depth did not (p > 0.05)
Summary
Ultrasound (US) elastography is a noninvasive imaging modality for assessment of tissue stiffness. US elastography techniques can be classified as shear wave or strain imaging [1,2], and three modalities are available for shear wave imaging: transient elastography, point shear wave speed measurement, and shear wave speed imaging. Shear waves are generated by controlled external vibrations in transient elastography (Fibroscan, Echogen), and by acoustic radiation force impulses in point shear wave speed measurement (Virtual Touch Quantification [VTQ]; EPIQ 5) and shear wave speed imaging (Virtual Touch Image Quantification [VTIQ]; Aixplorer; Aplio) [1]. New US elastography systems are currently being developed, and US shear wave elastography has been approved for clinical use by the United States Food and Drug Administration (FDA). To validate shear wave elastography as a quantitative imaging biomarker, its accuracy and precision should be guaranteed. Accuracy and precision are essential and fundamental for quantitative imaging modalities [3]
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