Editorial: Innovations in MR hardware from ultra-low to ultra-high field - Frass-Kriegl, Roberta; Broche, Lionel Marc; Ginefri, Jean-Christophe; Ladd, Mark E.; Roat, Sigrun; Sarracanie, Mathieu; Winkler, Simone Angela S.; Laistler, Elmar (Frontiers in Physics, 2022)