Human soleus muscle architecture at different ankle joint angles from magnetic resonance diffusion tensor imaging

Area of Science:

• Biomechanics
• Medical Imaging
• Human Anatomy

Background:

• Muscle fiber orientation is crucial for physiological cross-sectional area, force production, and mechanics.
• Determining in vivo muscle architecture, especially in complex structures like the human soleus, presents significant challenges.

Purpose of the Study:

• To map the in vivo fiber architecture of the human soleus muscle at rest.
• To investigate changes in soleus fiber architecture between neutral and plantarflexed ankle positions using diffusion tensor imaging (DTI).

Main Methods:

• Employed MRI-based diffusion tensor imaging (DTI) at 3 Tesla on six subjects.
• Acquired DTI data in neutral and plantarflexed ankle positions.
• Analyzed diffusion tensor eigenvalues, fractional anisotropy (FA), and eigenvector orientations in soleus subcompartments post-denoising.

Main Results:

• DTI-derived fiber architecture aligned with previous cadaver-based models.
• Increased plantarflexion led to a ~14% rise in diffusion tensor eigenvalues across all soleus subcompartments.
• Fractional anisotropy (FA) showed varied trends (decrease in posterior/marginal, increase in anterior soleus).
• Significant eigenvector angle changes observed: ~41° in posterior and ~48° in anterior soleus with plantarflexion.

Conclusions:

• DTI provides detailed, subject-specific in vivo muscle architecture data for the human soleus.
• Ankle position significantly influences soleus fiber orientation and diffusion properties.
• These findings support the use of DTI for advanced modeling of muscle performance and disease-related changes.