Effect of passive muscle length change on apparent diffusion coefficient: Detection with clinical MR imaging

Purpose: We investigated whether change in muscle microstructure associated with passive extension and contraction affects proton diffusivity. Material and Methods: In 6 male subjects, we compared apparent diffusion coefficients (ADC) along the posterior-to-anterior (ADC-PA), right-to-left (ADC-RL) and superior-to-inferior (ADC-SI) directions of the right tibialis anterior muscle with the ankle joint in passive plantar flexion and passive dorsiflexion. Results: Compared to the respective ADCs at plantar flexion, the ADC-PA (P=0.002) and ADC-RL (P=0.008) were significantly greater, but ADC-SI (P=0.008) significantly lower at dorsiflexion. Conclusion: Our results indicate that change in muscle microstructure associated with passive extension and contraction would affect proton diffusivity, and this alteration of proton diffusivity could be detected by measuring ADC with a clinical magnetic resonance scanner.