title: A two-step optical flow method for strain estimation in elastography: Simulation and phantom study.
abstract: Optical flow (OF) method has been used in ultrasound elastography to estimate the strain distribution in tissues. However the bias of strain estimation by OF has previously been shown to be close to 20%. The objective in this paper is to improve the performance of OF-based strain estimation, a two-step OF method with a local warping technique is proposed in this paper. The local warping technique effectively decreases the decorrelation of the signals, and hence improves the performance of strain estimation. Simulations on both homogeneous and heterogeneous models with different strains are performed. Experiments on a heterogeneous tissue-mimicking phantom are also carried out. Simulation results of the homogeneous model show that the two-step OF method reduces the bias of strain estimation from 23.77% to 1.65%, and reduces the standard deviation of strain estimation from 2.9×10(-3) to 0.47×10(-3). Simulation results of the heterogeneous model shows that the signals-to-noise ratio (SNRe) of strain estimation is improved by 2.1 and 5.3dB in the inclusion and background, respectively, and the contrast-to-noise ratio (CNRe) is improved by 6.8dB. Finally, results of phantom experiments show that, by using the proposed method, the SNRe is increased by 4.0dB and 8.9dB in the inclusion and background, respectively, while the CNRe is increased by 13.1dB. The proposed two-step OF method is thus demonstrated capable of improving the performance of strain estimation in OF-based elastography.
authors.affiliation: Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing 100084, China.
authors.forename: Xiaochang
authors.initials: X
authors.lastname: Pan
authors.affiliation: Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing 100084, China; Center for Biomedical Imaging Research, Tsinghua University, Beijing 100084, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Gao
authors.affiliation: Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing 100084, China.
authors.forename: Shengzhen
authors.initials: S
authors.lastname: Tao
authors.affiliation: Division of Electronics and Information Technology, National Institute of Metrology, Beijing 100013, China.
authors.forename: Ke
authors.initials: K
authors.lastname: Liu
authors.affiliation: Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing 100084, China. Electronic address: deabj@tsinghua.edu.cn.
authors.forename: Jing
authors.initials: J
authors.lastname: Bai
authors.affiliation: Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing 100084, China; Center for Biomedical Imaging Research, Tsinghua University, Beijing 100084, China. Electronic address: luo_jianwen@tsinghua.edu.cn.
authors.forename: Jianwen
authors.initials: J
authors.lastname: Luo
mesh_terms: D003198:Computer Simulation; D054459:Elasticity Imaging Techniques / Q000379:methods*; D015233:Models, Statistical; D019047:Phantoms, Imaging; D059629:Signal-To-Noise Ratio; D013314:Stress, Mechanical
keywords: Elastography; Local warping; Optical flow; Strain estimation