Background: In ultrasound elastography, reconstruction of tissue elasticity\n(e.g., Youngâ��s modulus) requires regularization and known information of forces\nand/or displacements on tissue boundaries. In practice, it is challenging to choose an\nappropriate regularization parameter; and the boundary conditions are difficult to\nobtain in vivo. The purpose of this study is to develop a more applicable algorithm that\ndoes not need any regularization or boundary force/displacement information.\nMethods: The proposed method adopts the bicubic B-spline as the tissue motion\nmodel to estimate the displacement fields. Then the estimated displacements are input\nto the finite element inversion scheme to reconstruct the Youngâ��s modulus of each\nelement. In the inversion, a modulus boundary condition is used instead of force/\ndisplacement boundary conditions. Simulation and experiments on tissue-mimicking\nphantoms are carried out to test the proposed method.\nResults: The simulation results demonstrate that Youngâ��s modulus reconstruction of the\nproposed method has a relative error of ?3.43 �± 0.43% and root-squared-mean error of\n16.94 �± 0.25%. The phantom experimental results show that the target hardening artifacts\nin the strain images are significantly reduced in the Youngâ��s modulus images. In both\nsimulation and phantom studies, the size and position of inclusions can be accurately\ndepicted in the modulus images.\nConclusions: The proposed method can reconstruct tissue Youngâ��s modulus distribution\nwith a high accuracy. It can reduce the artifacts shown in the strain image and correctly\ndelineate the locations and sizes of inclusions. Unlike most modulus reconstruction\nmethods, it does not need any regularization during the inversion procedure.\nFurthermore, it does not need to measure the boundary conditions of displacement or\nforce. Thus this method can be used with a freehand scan, which facilitates its usage in\nthe clinic.
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