Potassium (39K) & Sodium (23Na) MRI of dystrophic skeletal muscle tissue at 7T: impact of fatty infiltration on measured tissue ion concentrations

Motivation: Combined 23Na/39K MRI at 7T can highlight ion disturbances related to patho-physiological processes within dystrophic muscle tissue. However, quantification of the apparent tissue potassium concentration (aTPC) using 39K MRI is challenging due to low signal-to-noise and rapid signal decay. Goal(s): Here, we investigated the feasibility of quantitative 39K MRI in dystrophic muscle tissue. Approach: The lower leg of 14 FSHD patients and 11 healthy controls was examined using 39K/23Na and 1H MRI at 7T. Results: We found a strongly reduced aTPC in fat infiltrated muscles. After correction for reduced potassium concentration in fat, aTPC values in dystrophic muscles were similar to healthy muscles. Impact: Potassium concentration in fatty tissue is strongly reduced compared to healthy skeletal muscle tissue. This has to be considered when investigating and interpreting aTPC values measured with 39K MRI in fat-replaced skeletal muscle tissue.