Reliability and robustness of muscle architecture measurements obtained using diffusion tensor imaging with anatomically constrained tractography

For detailed analyses of muscle adaptation mechanisms during growth, ageing or disease, reliable measurements of muscle architecture are required. Diffusion tensor imaging (DTI) and DTI tractography have been used to reconstruct the architecture of human muscles in vivo. However, muscle architecture measurements reconstructed with conventional DTI techniques are often anatomically implausible because the reconstructed fascicles do not terminate on aponeuroses, as real muscle fascicles are known to do. In this study, we tested the reliability of an anatomically constrained DTI-based method for measuring three-dimensional muscle architecture. Anatomical magnetic resonance images and diffusion tensor images were obtained from the left legs of eight healthy participants on two occasions one week apart. Muscle volumes, fascicle lengths, pennation angles and fascicle curvatures were measured in the medial and lateral gastrocnemius, soleus and the tibialis anterior muscles. Averaged across muscles, the intraclass correlation coefficient was 0.99 for muscle volume, 0.81 for fascicle length, 0.73 for pennation angle and 0.76 for fascicle curvature. Measurements of muscle architecture obtained using conventional DTI tractography were highly sensitive to variations in the stopping criteria for DTI tractography. The application of anatomical constraints reduced this sensitivity significantly. This study demonstrates that anatomically constrained DTI tractography can provide reliable and robust three-dimensional measurements of whole-muscle architecture. The algorithms used to constrain tractography have been made publicly available.