Osmotic effects on the T-2 relaxation decay of in vivo muscle

Saline solutions are commonly employed as a vehicle for drugs administered intramuscularly. In this study, in vivo measurements of spin-spin relaxatio n (T-2) processes by magnetic resonance imaging (MRI) were performed to inv estigate the distribution of water in rat masseter muscle tissue after intr amuscular injection of saline solutions of varying tonicity. Prior to salin e injection, image-based T-2 relaxation decay of muscle was monoexponential . After injection of saline, the T-2 relaxation decay became multiexponenti al. Non-negative least squares (NNLS) analysis of the decay curves revealed two relaxation components: a fast component (T-2 = 20-40 ms) and a slow co mponent (T-2 = 150-400 ms), which are assigned to intra- and extracellular water protons, respectively. Injection of hypertonic saline solutions signi ficantly increased the extracellular water component in muscle tissue compa red to isotonic saline solutions, an effect which lasted for more than 60 m in. These findings suggest that MRI techniques may be useful to investigate the effect of hyper- or hypotonic solutions on muscle tissue in vivo. (C) 2001 Wiley-Liss, Inc.