Performance comparison of optical flow and block matching methods in shearing and rotating models

Abstract

Accurate estimation of myocardial motion based on ultrasound imaging is of great value for evaluation of cardiac function. Typically, myocardium undergoes complex motion and deformation including shear deformation and rotation. Thus a compression model is insufficient for investigating the performance of different algorithms. In this study, simulated shearing and rotating models are used to study the performance of optical flow (OF) and block matching (BM) methods based on ultrasound radio-frequency (RF) data. A deforming model was simulated with applied axial shear strains of 2- 6%, respectively. In addition, a rotating model was simulated with rotation angles of 0.5°-4°, respectively. Axial strains of 0%, 1% and 2% were also applied to these two models to study the influence of applied strain on the estimation of axial shear strain and rotation. To quantify the estimation performance, the root mean square error (RMSE) was used as the evaluation criterion. The results show that OF has lower RMSEs of the estimated displacement, strain and rotation angle than BM, especially at large axial shear strains and rotation angles. For the shearing model, the RMSEs of axial strains, lateral strains, and axial shear strains are reduced by up to 95.5%, 70.3% and 90.0%, respectively. For the rotating model, the RMSEs of axial strains, lateral strains, and rotation angles are reduced by up to 96.9%, 93.4% and 89.7%, respectively. OF is proved to outperform BM and thus is recommended to be used for shear strain and rotation estimation. The validations of phantom and in-vivo experiments are still required.