This paper considers the following two cases of missing cone problem: the limited angle tomography and time-varying object tomography.Based on the spatial and Fourier domain properties of Radon transform

a sinogram extrapolation technique is proposed.The missing data in sinogram is extrapolated using a novel least mean square error criterion and a complete sinogram can be restored. This complete sinogram is then used for image reconstruction by standard methods. The derivation of the sinogram extrapolation formulations is given. An iterative algorithm for solving these formulations is also given. Computer simulation results are presented to demonstrate the efficiency of the proposed technique.