Bringing GRAPPA to non-Cartesian MRI through SPARKLING: An application to MP-RAGE anatomical MRI

Motivation: Well established clinically used parallel imaging techniques like GRAPPA and CAIPIRINHA are mostly limited to Cartesian sampling, and their extension to non-Cartesian sampling is not direct. Goal(s): We propose to extend the SPARKLING framework to ensure GRAPPA accelerated Cartesian sampling in k-space center, while allowing non-Cartesian sampling in the periphery. Approach: Through affine constraints, we can enforce Cartesian acceleration in the center of k-space, while allowing non-Cartesian sampling in the periphery. Results: Using 2x2 GRAPPA with SPARKLING trajectories for anatomical MRI with MPRAGE sequences enables 10x acceleration, achieving 1mm isotropic whole-brain scans in 1 minute. Impact: This novel technique will help bring conventional multi-coil acceleration to non-Cartesian imaging, which can be used independently to massively accelerate MR scans, enabling faster and higher resolution imaging, which will be beneficial for varied clinical applications.