Cancellation of motion artifact in MRI due to 2D rigid translational motion

A new algorithm for cancelling MRI artifact due to translational motion in the image plane is described. Unlike the conventional iterative phase retrieval algorithm, in which there is no guarantee for the convergence, a direct method for estimating the motion is proposed. In the previous approach, the motions in the readout(x-) direction and the phase encoding(y-) direction are estimated simultaneously. However, the feature of the each x- and y-directional motion is different. Based on the analysis of their features, each x- and y-directional motion is cancelled by different algorithms in two steps. First, we notice that the x-directional motion corresponds to a shift of the x-directional spectrum of the MRI signal, so the x-directional motion can be cancelled by shifting the spectrum in inverse direction. Next, the y-directional motion is cancelled using a new constraint, with which the motion component and the true image component can be separated. The algorithm is shown to be effective by simulations. (C) 1997 Elsevier Science Ltd.