Correcting corrupted-phases by blood perfusion, diffusion and body motion in MRI imaging.

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When taking perfusion or diffusion images of small flow, artifact is easily caused by body motion. In this research, we developed artifact correction algorithms for translational, rotational, and expanding-shrinking body motions.(1) Translational rigid body motion : Using the fact that Fourier transform F (x, n) of MRI signal f (x, n) in the n-th view (phase encode) shows the object position along the frequency axis (x), we corrected the corrupted phases by a body motion. We have also developed a method which can correct independently of x-axis the body motion alosng y-axis.(2) Rotational rigid body motion : For a step rotation with unkown rot ation center and rotation angle, first we estimated the rotaion angle so that energy in outside region of the reconstructed image becomes minimum. Then we applied the phase retreaval algorithm to reduce the phase disturbance caused by the off-origin of the rotation center.(3) Expanding-shrinking deformable body motion : In case of such as abdomen expanding and shrinking proportionally in x-and y-axs, we have shown that we can reduce the artifact by ; first obtain x-directional motion from the projection onto the frequency axis as the same as (1), and then correct phases corresponding to y-axis by the phase retreaval algorithm.These algorithms can also be applied to the artifact correction caused by body motion of child and old person who cannot lay still for the image taking time of several to several ten minutes with conventional MRI.In order to make the algorithm more close to the practical use, it's a future task to model the more flexible motion with more number of freedom.