Coil reduction in parallel excitation with large array

Parallel excitation using coil array has been introduced in MRI as an effective method to design multi-dimensional spatially selective RF pulses. Generally, all transmit coil elements are used simultaneously in parallel excitation. In case of large array, RF pulse design requires significant computation time and memory size. In this paper, a method using reduced number of coils for parallel excitation is proposed to take advantage of localized coil transmit sensitivity in large array. Specifically, a subset of coils in the large array can be selected based on coil sensitivity coverage and desired excitation pattern. Simulation results with both spiral and EPI k-space trajectories show that proposed method is effective in achieving high excitation resolution at different acceleration factors while the computation time and memory requirement are greatly reduced.