A 3D MRI image is acquired as a series of spherical shells of increasing
radius. Each shell is sampled by one or more interleaved spiral sampling
trajectories and to shorten the scan time one or more spiral sampling
trajectories are skipped in the larger shells that sample the periphery
of k-space. Motion correction of the acquired k-space data is
accomplished by reconstructing tracking images from each of the shells
and locating markers therein which indicate object movement from a
reference position. The k-space data is corrected using this movement
information.