Accelerated 2D Cartesian MRI 

We designed an 8-channel local B0 coil array, with a 16-transmit/32-receive RF coil within its support, to investigate the ultimate image acceleration by nearly arbitrary spatial-temporal gradient modulations, as a more general technique than wave-CAIPI and FRONSAC. To understand the sampling behaviors for different field shapes with an optional combination with RF receivers’ sensitivity, we extend a mathematical framework for parallel imaging based on reproducing kernel Hilbert space, and visualize the spin precession sampling in a quantitative k-space encoded by the nonlinear B0 fields, within arbitrary acquisition durations (e.g., one or all phase encoded steps) to examine the optimal modulation field and trajectory for 2D Cartesian MRI. Additionally, a mathematical algorithm based on subspace signal extraction (i.e., extending ESPIRiT) is developed to improve the local B0 field estimations and image reconstruction. Finally, with a comprehensive safety evaluation including B-field, E-field, PNS stimulation and acoustic measurements, in-vivo accelerated scans with local B0 coil modulations have been performed to validate our methodology, as a significant step to push the MRI speed further with local B0 coil array and arbitrary gradient modulations.