Diffusion tensor imaging of the human calf muscle: Distinct changes in fractional anisotropy and mean diffusion due to passive muscle shortening and stretching

Abstract

The influence of passive shortening and stretching of the calf muscles on diffusion characteristics was investigated. The diffusion tensor was measured in transverse slices through the lower leg of eight healthy volunteers (29±7 years) on a 3 T whole-body MR unit in three different positions of the foot (40° plantarflexion, neutral ankle position (0°), and -10° dorsiflexion in the ankle). Maps of the mean diffusivity, the three eigenvalues of the tensor and fractional anisotropy (FA) were calculated. Results revealed a distinct dependence of the mean diffusivity and FA on the foot position and the related shortening and stretching of the muscle groups. The tibialis anterior muscle showed a significant increase of 19% in FA with increasing dorsiflexion, while the FA of the antagonists significantly decreased (∼20%). Regarding the mean diffusivity of the diffusion tensor, the muscle groups showed an opposed response to muscle elongation and shortening. Regarding the eigenvalues of the diffusion tensor, λ2 and λ3 showed significant changes in relation to muscle length. In contrast, no change in λ1 could be found. This work reveals significant changes in diffusional characteristics induced by passive muscle shortening and stretching. Copyright © 2009 John Wiley & Sons, Ltd.