Abstract: To estimate the motion information in the region of interest(ROI),firstly central slice theorem is generalized and differential constraint condition is derived. Secondly,the finite Hilbert transform algorithm is adopted to evaluate the partial derivatives of image function along the azimuthal and radial directions,respectively. Finally,the motion vector feld in the polar coordinate system is determined by an improved equation of opticN flow. Compared wim general motion estimate methods,the proposed method is not required to calculate the derivatives using the difference operation in image domain,therefore may show a much higher accuracy,and the motion vector field in the polar coordinate system is much suitable for medical diagnostic requirement. The feasibility of the proposed algorithm has been also validated by using numerical simulation