Non-idealized system (NIS) optimization of EPI sequences at ultra-high field.

Motivation: MRI scanners are built under the assumption of near perfect responses of each subsystem. Computing advances mean that this may no longer be necessary, enabling exploration of cheaper, efficient alternatives. Goal(s): To allow high-performance scanning with less emphasis on hardware performance, reducing costs and improving access. Approach: We consider non-idealized system optimization where hardware imperfections are built into a forward model used to optimize pulse sequences via the MR-zero framework. We experimentally demonstrate NIS using measured GIRFs from a 7T system to optimize EPI sequences. Results: NIS optimization produces sequences that substantially reduce image artefacts even for scenarios that previously exceeded hardware constraints. Impact: NIS optimization embraces gradient system imperfections, discovering novel acquisition strategies to inherently mitigate them. Although demonstrated on a state-of-the-art 7T scanner, the concept of including imperfections directly into sequence design offers a means to maximize performance of any scanner hardware.