Magnetic resonance trajectory correcting with GRAPPA operator gridding

摘要

Apparatus, methods, and other embodiments associated with magnetic resonance (MR) trajectory correcting using GRAPPA operator gridding (GROG) are described. One example method includes identifying an on angle or regular portion of a projection in an MR trajectory and then computing base GROG weights for that portion. The example method includes identifying a shift direction and a shift amount for the projection. The shift direction is configured to shift the projection towards a desired point in k-space and the shift amount is configured to shift the projection by a desired amount in the shift direction. With a shift direction and amount available, the example method corrects for a gradient delay by manipulating the MR source signal data using the shift direction and the shift amount. In one embodiment, a gradient delay can be determined and used to calibrate an MRI apparatus.

主权项

1. A trajectory correcting method that is performed by a computer in a magnetic resonance (MR) apparatus, the method comprising:
identifying with the computer of the MR apparatus, a portion of a set of MR source signal data associated with on-angle portions of a set of projections in an MR trajectory, where the MR source signal data is electronic data that has been acquired by the MR apparatus; determining with the computer of the MR apparatus, a set of base GROG weights for the on angle portions of the set of projections in an MR trajectory, where the GROG weights are GRAPPA operator gridding (GROG) weights, GRAPPA being a generalized auto-calibrating partially parallel acquisition technique; identifying a shift direction for an individual projection, from the set of projections in an MR trajectory where the shift direction facilitates shifting the individual projection towards a desired point in k-space;
where identifying the shift direction of an individual projection, from the set of projections in an MR trajectory comprises:
determining, with the computer of the MR apparatus, an estimate of the center of k-space; with the estimate of center of k-space being determined from a measured echo-peak magnitude (EPM) from within the set of MR source signal data that is associated with the on-angle portions, of the set of projections, of an MR trajectory;generating, a set of candidate points from the on-angle portions of the set of MR source signal data, with the computer of the MR apparatus; andselecting the shift direction based, at least in part, on a re-determining of the estimate of the center of k-space using the set of computer generated candidate points; identifying a shift amount for the individual projection, with the computer of the MR apparatus by comparing, an initial estimate for the location of center of k-space and a final estimate for the location of the center of k-space; where the shift amount facilitates shifting the individual projection by a desired amount in the shift direction; manipulating the set of MR source signal data based, at least in part, on the shift direction and the shift amount identified for the individual projection, by shifting the on-angle portions, of the set of projections of the MR source signal data in the identified shift direction, by the identified shift amount and thereby align the set of projections in order to have the individual projection(s) pass through the desired point in k-space; and reconstructing a magnetic resonance image from the manipulated MR source signal data with the computer of the MRI apparatus.