A recurring need in MRI and MRS is to acquire signals from multiple nuclei, 1H proton and 23Na sodium, in the same study. However, a dual-tune volume coil implemented in a single structure leads to SNR and B1-efficiency penalties for the X-nucleus. We numerically investigated how B1-fields interact between either a traveling-wave coil existing outside the bore, or a local dipole array, paired with a birdcage 23Na-coil. For applications to head and knee imaging at 7T, an easily-implemented traveling-wave coil may provide sufficient proton signal for anatomical localization and B0 shimming, without significantly reducing the performance of the X-nucleus coil.
