A Reliability Index of Shear Wave Speed Measurement for Shear Wave Elastography

Shear wave elastography is widely used for the noninvasive measurement of tissue stiffness. Assessing liver fibrosis, for example, by measuring shear wave propagation speed is gaining popularity. Elastography data, however, is often contaminated with low SNR and the results become unreliable. Quantification of the reliability of shear wave measurement, therefore, has a significant practical importance. We propose a performance index called "Reliability Measurement Index (RMI)" which is calculated by the weighted sum of two factors: the residual of the wave equation and the magnitude of the shear wave. The residual error accounts for the deviation from the wave equation due to error sources including measurement noises and motion artifacts. Magnitude of induced shear wave is also used to reflect the SNR of the signal. The proposed approach has been successfully implemented on a commercial diagnostic ultrasound system (RS-80A with Prestige, Samsung Medison, Korea). The proposed performance index has been tested in both phantom and in-vivo studies. Initial studies show that high values of RMI are strongly correlated with reproducible measurements. The proposed index can be utilized to filter out unreliable measurements and result in performance improvement of shear wave elastography.