On the correlation between T₂ and tissue diffusion coefficients in exercised muscle: Quantitative measurements at 3T within the tibialis anterior

Purpose: To assess the transverse relaxation time T₂ and diffusion coefficient D before and following exercise in the tibialis anterior muscle and determine whether T₂ and D values were correlated. Methods: Measurements of T₂ and D were performed at 3 T within axial slices through the calf muscles of six healthy volunteers at 95 s intervals before and for 10-12 min after a dorsiflexion exercise to exhaustion. Results: The mean ± standard deviation (SD) of T₂ and D before exercise were 32 ± 1.55 ms and 1.52 ± 0.15 μm²/ms, and after exercise were 43 ± 2.5 ms and 1.72 ± 0.13 μm²/ms, respectively. The mean ± SD inter-individual recovery times of the % change in T₂ and D after exercise were 7.9 ± 4.2 and 10.9 ± 7.0 min, respectively. The T₂ and D values showed a significant correlation throughout the experiments (r ² = 0.45). Conclusions: The increase in T₂ of skeletal muscle after exercise is correlated with the increase of the diffusion coefficient D and the recovery times appear similar, indicating that any model used to explain T₂ increases with exercise must also account for increased diffusion coefficients.