Assessment of Human Skeletal Muscle Contraction and Force by Diffusion Tensor Imaging

We aimed to investigate the association between mobility and skeletal muscle strength by using magnetic resonance diffusion tensor imaging (DTI). This study included 20 healthy male volunteers (mean age, 21.8 ± 1.1 years). The maximum voluntary strength (MVC) of each participant was measured with the ankle joint in plantar and dorsal flexion using an instrument for measuring muscle strength. Moreover, magnetic resonance imaging (MRI) was performed with the ankle joint at rest, in plantar flexion, and in dorsal flexion. For imaging, a 1.5-T MRI device was used, and a diffusion-weighted stimulated echo-planar imaging pulse sequence. Tensor eigenvalues (λ), fractional anisotropy (FA), and the apparent diffusion coefficient (ADC) were calculated from data obtained by DTI. The resulting MRI data were compared to the data on muscle mobility or strength and statistically analyzed. Regarding changes in DTI indices during muscle movements, anisotropy of the tibialis anterior was significantly increased from rest to plantar flexion (P < 0.01), whereas no significant change was observed in dorsal flexion (n.s.). In contrast, the extent of significant changes in anisotropy of the medial gastrocnemius (mGC) and soleus (SOL) was small at plantar flexion (mGC, P < 0.01; SOL, n.s.), whereas the indices were significantly increased at dorsal flexion (P < 0.01). Regarding the correlation between MVC of each skeletal muscle and the DTI indices, FA and λ3 were significantly correlated in movements involving the muscles, whereas no significant correlation was observed in movements not involving them. Changes in intramuscular water molecules by elongation and contraction of the skeletal muscle fibers could be assumed to affect changes in diffusional anisotropy. When muscles contract, the space between myocytes was reduced and they might become increasingly dense. Moreover, diffusional anisotropy increased with Corresponding author.