Multicomponent T2 relaxation of in vivo skeletal muscle.

In vivo spin-spin (T2) relaxation measurements were acquired from the flexor digitorum profundus (FDP) of 13 subjects. A standard imaging T2 measurement technique [number of points (N) = 6, TE = 18 msec, signal-to-noise ratio (SNR) approximately equal to 300] yielded a single T2 value of 31 msec. A novel technique, projection presaturation combined with a CPMG sequence, was used to acquire data (N = 1000, TE = 1.2 msec, SNR 3500) from a cylindrical voxel (2 cm diameter, 5 cm length) within the FDP. All 13 subjects had at least four T2 components, at < 5, 21 +/- 4, 39 +/- 6, and 114 +/- 31 msec, with fractional areas of 11 +/- 2, 28 +/- 15, 46 +/- 12, and 11 +/- 5% respectively. The shortest and longest components have been observed in ex vivo muscle studies, probably corresponding to water associated with macromolecules and extracellular water, respectively. The middle T2 components are suggestive of an organization of in vivo intracellular water.