P1A-1 An Alternative Technique of Displacements Synthetic Reconstruction in Transient Elastography

Soft tissue elasticity can be measured in radiation force transient elastography by following shear waves propagation through the medium. These waves are created in the medium by an ultrasound radiation force generated by a focused transducer. To follow the shear waves propagation, we measure displacements induced by these waves through the medium using a 5 MHz linear array transducer connected to an ultrasound imaging system. We propose in this work an alternative multi-element imaging system which requires a transmit/receive system with only one transmit channel and one receive channel. The medium image is then beamformed using synthetic transmit/receive subapertures in which a focusing in reception is used. A synthetic reconstruction method with contributions of only few elements (to reduce the experiment time) is used to reconstruct the medium image. This reconstruction method is tested and validated on a cylindrical metallic target. After that, we test the performance of our imaging system on a tissue-mimicking phantom by reconstructing the medium image at different times (during shear wave propagation) and measuring displacements using inter-correlated ultrasound methods on the reconstructed images. The sensitivity of the displacement estimator depends on several parameters (sampling frequency, transducer characteristics, kernel length, signal-to-noise ratio (SNR) of the tracked radio-frequency (RF) lines. Since the SNR of the beamformed image lines depends on the reconstruction method used, a second reconstruction method was proposed to enhance the SNR of the beamformed RF lines and, thus, reduce the noise level of displacement estimation. In this method, more contributions of RF lines are added to beamform RF lines of the medium image. The two methods are then compared in terms of robustness and sensitivity