Abstract: In order to get accurate strain estimation in ultrasound elastography， it is important to eliminate the decorrelation caused by the lateral displacement of the longitudinal compression. A new strain estimation method was proposed by combining the twodimensional companding and optical flow method. First， the twodimensional Hibert transformation was used to convert the original ultrasound RF signals to the analytical signals by the envelop detection. Then， the block matching method was used to get the motion vectors of 16 subblocks. Based on the motion vectors， a linear regression method was used to estimate the parameters of the twodimensional companding. After the twodimensional companding， the optical flow method was employed to estimate the subpixel motion. Experimental results showed that the overall strain estimation accuracy and robustness could be enhanced by the proposed twodimensional companding methods. The longitudinal displacement and longitudinal strain obtained by the proposed method were basically consistent with those obtained by the finite element simulation， which proved the correctness of the new method.

Key words: ultrasound, elastography, optical flow method, 2D companding, strain estimation