Using self-consistency for an iterative trajectory adjustment (SCITA).

PURPOSE: To iteratively correct for deviations in radial trajectories with no need of additionally performed calibration scans. THEORY AND METHODS: Radially acquired data sets-even when undersampled to a certain extend-inherently feature an oversampled area in the center of k-space. Thus, for a perfectly measured trajectory and neglecting noise, information is consistent between multiple measurements gridded to the same Cartesian position within this region. In the case of erroneous coordinates, this accordance-and therefore a correction of the trajectory-can be enforced by an algorithm iteratively shifting the projections with respect to each other by applying the GRAPPA operator. The method was validated in numerical simulations, as well as in radial acquisitions of a phantom and in vivo images at 3T. The results of the correction were compared to a previously proposed correction method.
RESULTS: The newly introduced technique allowed for a reliable trajectory correction in each of the presented examples. The method was able to remove artifacts as effectively as methods that are based on data from additional calibration scans.
CONCLUSION: The iterative technique introduced in this paper allows for a correction of trajectory errors in radial imaging with no need for additional calibration data.