Peak assignment in localized 1H MR spectra of human muscle based on oral creatine supplementation

1H-MR spectra of human skeletal muscle feature peak splittings due to dipolar coupling. Quantitative difference spectroscopy in a double-blind cross-over trial testing oral creatine supplementation revealed that most of the resonances affected by dipolar coupling can be assigned to creatine and/or phosphocreatine. The assignment was performed in two different skeletal muscles and confirmed by measurements at the magic angle where dipolar splittings vanish. Numerical spectral simulations revealed that the observed spectra are consistent with partly-averaged dipolar coupling among methylene and methyl protons of (phospho)creatine. The possible nature of the molecular dynamics leading to incomplete dipolar averaging is discussed.