Design of non-selective refocusing pulses with phase-free rotation axis by gradient ascent pulse engineering algorithm in parallel transmission at 7Â T

► We report a new MRI radiofrequency pulse design algorithm based on optimal control. ► Spin refocusing non-uniformities are addressed using tailored RF pulses. ► The target rotation matrix is synthesized with a phase-free rotation axis. ► In vitro spin-echo experiments demonstrate the potential of the optimization algorithm. ► Performance obtained is quantified using Quantum Process Tomography.