Purpose: To elucidate changes in the diffusion properties of muscle fiber between rest and active contraction.
Methods and materials: In 10 healthy adult volunteers (4 men, 6 women), we obtained diffusion tensor (DT) images (b=500 s/mm(2)) of bilateral calves using a 1.5-tesla clinical magnetic resonance (MR) imager. We first simultaneously scanned both calves at rest, then obtained scans of bilateral calves with plantar flexion of the right ankle using the same imaging parameters. We measured fractional anisotropy (FA) and lambda(1), lambda(2), and lambda(3) in the gastrocnemius medialis (GCM) and anterior tibialis (AT) muscles of both calves by seeding the region of interest at the thickest part, then calculated the right-to-left ratio of the FA and eigenvalues in each muscle and compared each ratio between rest and contraction by paired t-test.
Results: In the GCM, the FA ratio increased from 1.05 at rest to 1.17 after contraction, and contraction elevated the lambda1 and 2 ratios from 0.99 in resting muscles to 1.06 (lambda(1)) and 1.07 (lambda(2)). In contrast, the AT showed a decrease of the lambda(1) ratio from 0.99 at rest to 0.96 at elongation and of the lambda(2) ratio, from and 1.01 at rest to 0.94 at elongation. Statistically significant differences were observed in the FA (P<0.05), lambda1 and lambda2 (P<0.01) in the GCM, and the lambda1 and lambda2 (P<0.05) in the AT.
Conclusion: The higher FA and lambda(1) and lambda(2) values of muscles at contraction than rest presumably reflect complicated changes, including microscopic morphological changes of the diffusion-restricting factor, focal temperature, and perfusion. We found that change in perfusion could affect the AT, and changes in focal perfusion and temperature could influence the GCM.