To validate the feasibility of quantitative combined potassium (³⁹K) and sodium (²³Na) MRI in human calf muscle tissue, as well as to evaluate the reproducibility of the apparent tissue potassium concentration (aTPC) and apparent tissue sodium concentration (aTSC) determination in healthy muscle tissue.

Quantitative ²³Na and ³⁹K MRI acquisition protocols were implemented on a 7 T MR system. A double‐resonant ²³Na/³⁹K birdcage RF coil was used. Measurements of human lower leg were performed in a total acquisition time of TA_Na = 10:54 min/TA_K = 8:06 min and using a nominal spatial resolution of 2.5 × 2.5 × 15 mm³/7.5 × 7.5 × 30 mm³ for ²³Na/³⁹K MRI. Two aTSC and aTPC examinations in muscle tissue were performed during the same day on 10 healthy subjects.

The proposed acquisition and postprocessing workflow for ²³Na and ³⁹K MRI data sets provided reproducible aTSC and aTPC measurements. In human calf muscle tissue, the coefficient of variation between scan and re‐scan was 5.7% for both aTSC and aTPC determination. Overall, mean values of aTSC = (17 ± 1) mM and aTPC = (85 ± 5) mM were measured. Moreover, for ³⁹K in calf muscle tissue, components of = (1.2 ± 0.2) ms and = (7.9 ± 0.9) ms, as well as a residual quadrupolar interaction of = (143 ± 17) Hz, were determined. The fraction of the fast component was f = (58 ± 4)%.

Using the presented measurement and postprocessing approach, a reproducible aTSC and aTPC determination using ²³Na and ³⁹K MRI at 7 T in human skeletal muscle tissue is feasible in clinically acceptable acquisition durations.