Combined imaging of potassium and sodium in human skeletal muscle tissue at 7 T

Purpose To validate the feasibility of quantitative combined potassium (K-39) and sodium (Na-23) 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. Methods Quantitative(23)Na and(39)K MRI acquisition protocols were implemented on a 7 T MR system. A double-resonant(23)Na/K-39 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 x 2.5 x 15 mm(3)/7.5 x 7.5 x 30 mm(3)for(23)Na/K-39 MRI. Two aTSC and aTPC examinations in muscle tissue were performed during the same day on 10 healthy subjects. Results The proposed acquisition and postprocessing workflow for(23)Na and(39)K 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(39)K in calf muscle tissue,T2*components ofT2f*= (1.2 +/- 0.2) ms andT2s*= (7.9 +/- 0.9) ms, as well as a residual quadrupolar interaction of omega q over bar = (143 +/- 17) Hz, were determined. The fraction of the fast component was f = (58 +/- 4)%. Conclusion Using the presented measurement and postprocessing approach, a reproducible aTSC and aTPC determination using(23)Na and(39)K MRI at 7 T in human skeletal muscle tissue is feasible in clinically acceptable acquisition durations.