NMR of skeletal muscle. Differences in relaxation parameters related to extracellular/intracellular fluid spaces.

The relationships between the T1 and T2 relaxation times, tissue water content and extracellular fluid space of two types of skeletal muscle groups were studied in rabbits and rats by means of NMR proton spectroscopy (10 MHz). Although there was no significant difference in the total water content between muscles rich in type I (74.5 +/- .8%; soleus) or type II (75.0 +/- .7%; gastrocnemius) fibers, the respective T1 (521 +/- 25 vs. 486 +/- 16 millisecond; p less than .01) and T2 (39.5 +/- 1.8 vs. 36.5 +/- 1.0 millisecond; p less than .01) relaxation times were consistently prolonged. The longer relaxation times of the soleus as compared with the gastrocnemius muscle were related to a larger extracellular fluid space as measured by (35S) sulfate +34.5%; p less than .01). For this reason, it seems likely selective changes in these spaces will be detectable by NMR proton imaging.