Assessment of calf muscle contraction by diffusion tensor imaging

The goal of this study was to assess the changes of water diffusion during contraction and elongation of calf muscles using diffusion tensor (DT) MRI in normal volunteers. Twenty volunteers (mean age, 29 +/- 4 years) underwent DT MRI examination of the right calf. Echo planar imaging sequence was performed at rest, during dorsal flexion and during plantar flexion. The three eigenvalues (lambda 1, lambda 2, and lambda 3), apparent diffusion coefficient (ADC) and fractional anisotropy (FA) of the diffusion tensor were calculated for medial gastrocnemius (mGM) and tibialis anterior (TA). A fiber tractography was performed on both muscles. Non-parametric Wilcoxon and Mann Whitney tests were used for statistical evaluation. At rest, lambda 1, lambda 2 and ADC of mGM were higher than their counterparts of TA (P<0.01). During dorsal flexion, the three eigenvalues and ADC of TA significantly increased (P<0.05) as their counterparts of mGM slightly decreased (P=NS). Opposite variations were detected during plantar flexion of the foot. Visual analysis evidenced a relationship between 3D representations of MRI fibers and physiological state of muscles. Contraction of calf muscles produces changes in DT parameters, which are related to the physiological state of the muscle.