Joint Design of Excitation and Refocusing Pulses for Fast Spin Echo Sequences in Parallel Transmission

INTRODUCTION Fast spin echo (FSE) sequence [1] has been widely used in various MR applications, which, like other sequences, can suffer from the inhomogeneous B1 at high field. Parallel transmission of RF pulses [2, 3] has been shown to be quite effective in correcting B1 inhomogeneity. However, no FSE application with parallel transmission has been seen in the literature yet primarily due to the lack of method for designing parallel transmit pulses for FSE that satisfy the CPMG condition [4]. In this paper, we first show that designing excitation and refocusing pulse pair for FSE is a joint design problem. Then we formulate the design problem as a novel optimal control problem, where the optimal pulse pair is sought jointly to drive the magnetization vector to its desired state while maintaining the CPMG condition. Bloch simulation results are shown to demonstrate the superior performance of the pulses designed by the proposed method to those from conventional methods.