Advanced design of MRI inversion pulses for inhomogeneous field conditions by optimal control

Abstract

Non-selective inversion pulses find widespread use in MRI applications, where requirements on them are increasingly demanding. With the use of high and ultra-high field strength systems, robustness to $\Delta B_0$ and $B_1^{+}$ inhomogeneities, while tackling SAR and hardware limitations, has rapidly become important. In this work, we propose a time-optimal control framework for the optimization of $\Delta B_0$ - and $B_1^{+}$ -robust inversion pulses. Robustness is addressed by means of ensemble formulations, while allowing inclusion of hardware and energy limitations. The framework is flexible and performs excellently for various optimization goals. The optimization results are analyzed extensively in numerical experiments. Furthermore, they are validated, and compared with adiabatic RF pulses, in various phantom and in vivo measurements on a 3 T MRI system.

Keywords: Inhomogeneous B 0 and B 1 ; MRI; RF pulse design; time-optimal control.