Designing RF Refocusing Pulses for Parallel Transmit Spin Echo Sequences

Dan Xu¹, Kevin F. King¹

Most existing applications of parallel transmission have been restricted to gradient echo due to lack of systematic design of parallel transmit refocusing pulses. In this paper, we propose a new optimal control based method to design parallel transmit refocusing pulses for spin echo sequences with a single refocusing pulse per repetition time. The method addresses pulse nonlinearity by including Bloch equation in the formulation, designs pulses that refocus a spin ensemble, and optimizes nutation directions to achieve homogenous refocusing. Simulation results show that refocusing pulses designed by the proposed method produce better homogeneity than pulses designed by conventional methods.