A phantom study to cross-validate multimodality shear wave elastography techniques

Abstract

As various quantitative shear wave elastography techniques are being implemented commercially and used clinically, it is important to understand what elastic modulus is measured by those techniques and to assess technical factors influencing measurement accuracy. Cross-validated in this study were four shear wave elastography techniques including ultrasound elastography point quantification (ElastPQ), magnetic resonance elastography (MRE), 1-D transient elastography (TE), and a Verasonics ultrasound system based elastography feature. ElastPQ is an acoustic radiation force (ARF) based technique implemented on an ultrasound system iU22 for a curvilinear probe C5-1. MRE measurements were made at a shear wave frequency of 100 Hz. The 1-D TE system uses an external mechanical vibrator at 100 Hz to generate shear waves and a 7.5 MHz single element transducer to track shear wave propagation. The Verasonics ultrasound system with a linear probe L7-4 uses a plane wave transmit imaging mode to measure propagation speed of shear waves induced by ARF. Six custom-made elasticity phantoms were measured selectively and were assumed purely elastic by the four techniques. The results show good agreement between two ARF based techniques: ElastPQ and Verasonics based feature. When comparing ElastPQ to 1-D TE, the discrepancy for the hardest phantom could be explained by the diffraction artifact in the latter system. Further improvements on the 1D-TE reconstruction algorithm are ongoing. The overestimation by ElastPQ and Verasonics against MRE could be attributed to frequency dispersion due to slight viscosity in phantoms. MRE measures shear wave speed at a single frequency 100 Hz, whereas the other two estimate an effective group velocity over a larger bandwidth for a broadband shear wave signal. 1-D TE and MRE measurements are in closest agreement due to similar shear wave frequencies. More validation of these techniques is required on real patients in clinical settings.