Generalized GRAPPA operators for wider spiral bands: rapid self-calibrated parallel reconstruction for variable density spiral MRI.

A rapid and self-calibrated parallel imaging reconstruction method is proposed for undersampled variable density spiral datasets. A set of generalized GRAPPA for wider readout line operators are used to expand each acquired spiral line into a wider spiral band, therefore fulfilling Nyquist sampling criterion throughout the k-space. The calibration of generalized GRAPPA for wider readout line operators is performed using the fully sampled central k-space region. The resulting generalized GRAPPA for wider readout line operator weights are adaptively regularized to minimize the error in the newly-generated data at different k-space locations. Simulation and experimental results demonstrate that the technique can be used either to achieve a significant acceleration and/or to reduce off-resonance artifacts due to a shorten readout duration.