Shear wave elastography is commonly used for non-invasive evaluation of liver fibrosis. However, inter-system variability in data acquisition and processing methods can make it difficult to interpret and compare measurements from different systems. We are active participants on the RSNA QIBA Ultrasound Shear Wave Speed Biomarker Committee, which evaluates and proposes standardized methods for using shear wave speed measurements as a biomarker for staging liver fibrosis. Dr. Palmeri and Dr. Nightingale are members of the Systems Dependencies Subcommittee (co-chaired by Dr. Palmeri). Dr. Palmeri is also a member of the RSNA QIBA Magnetic Resonance Elastography Biomarker Committee.
Our specific efforts involve phantom calibration and analysis, as well as supporting an extensive finite element modeling effort to develop elastic and viscoelastic digital calibration phantoms for commercial systems. We have collaborated with other institutions and manufacturers around the world to develop simulation tools, standardized sequences, and data processing methods, which have been made publicly available:
- Source code for the digital phantoms on GitHub
- Digital phantom data on the Quantitative Imaging Data Warehouse (QIDW)
- Shear wave speed phantom sequences and processing code on GitHub
Dr. Palmeri conducted an AIUM Webinar that can be freely viewed online: “System-Dependent Factors Influencing Shear Wave Speed Measurements for Liver Fibrosis Characterization”.
The figure below shows shear waves propagating in a phantom with viscoelastic behavior similar to that observed in human liver. The shear waves were created with an acoustic radiation force impulse excitation using the proposed shear wave imaging sequence.
Current-generation ultrasound shear wave speed imaging systems were able to differentiate viscoelastic phantoms that modeled healthy, mildly fibrotic, and significantly fibrotic liver tissue (figure from Palmeri et al., 2015).
We have developed a standardized method for reporting group shear wave speeds and a phase velocity analysis, for the purpose of calibratingphantoms between different systems.
- Hall TJ, Milkowski A, Garra B, Carson P, Palmeri M, Nightingale K, et al. “RSNA/QIBA: shear wave speed as a biomarker for liver fibrosis staging,” Proceedings of the IEEE International Ultrasound Symposium, 2013. (https://doi.org/10.1109/ULTSYM.2013.0103)
- Palmeri M, Nightingale K, et al. “RSNA QIBA ultrasound shear wave speed phase II phantom study in viscoelastic media,” Proceedings of the 2015 IEEE Ultrasonics Symposium, 2015. (https://doi.org/10.1109/ULTSYM.2015.0283)
This work has been supported by the RSNA QIBA Ultrasound Shear Wave Speed Committee contract HHSN 268201300071C and FDA contract HHSF 223201400703P.