Pulsed NMR relaxometry of striated muscle fibers.

The longitudinal (T1) and transverse (T2) proton (1H) nuclear magnetic resonance (NMR) relaxation of fast- and slow-twitch muscle fibers are examined using rat muscle tissues in which one fiber type predominates. Both continuum and discrete exponential component fits are made to Carr-Purcell-Meiboom-Gill (CPMG) and inversion recovery pulse sequence measurements. In addition, experiments which illustrate the large sources of variability that have led to apparent conflicts in the literature are presented. Based on the results of this study, unique NMR features that distinguish fast- and slow-twitch muscle fibers are presented. The feasibility of differentiating fast- and slow-twitch muscle fibers using magnetic resonance (MR) imaging is briefly discussed.