Development of a Pulse Sequence with Alternating Excitation for Respiratory-Sorted B1+ and B0 Field Mapping in 23Na Human Torso MRI

23Na MRI is a promising imaging method, but suffers from lower SNR, hence from longer acquisition times and lower image resolution than 1H MRI. Especially in the torso, motion and magnetic field inhomogeneities impede quantitative analysis of 23Na concentrations. To tackle this, a new pulse sequence is presented that yields self-gated respiratory-sorted B1+ and B0 maps from a single measurement. B1+ mapping with the new sequence is less prone to motion artefacts, since k-space projections of two flip angles are acquired in an interleaved manner. This reduces the influence of varying respiration, which can lead to artefacts in conventional mapping.