Rapid autocorrection using prescan navigator echoes

Autocorrection is an adaptive motion correction algorithm that does not req uire an in vivo measurement of the motion record. A novel method for ensuri ng convergence of this algorithm when motion is severe is presented. A limi ted number of navigator echoes are acquired before the imaging sequence to obtain a "snap-shot" of the object. Phase differences between the navigator and image k-space data are used as an estimate of motion-induced phase shi fts in the image, followed by autocorrection. In phantom data a six-fold re duction in computation time compared to autocorrection alone was realized. These results indicate that this navigator/autocorrection combination may b e useful for reducing motion artifacts and computation time for MR exams wh en motion along the image phase encoding axis is severe. (C) 2000 Wiley-Lis s, Inc.