[Diffusion Tensor Imaging of Rotator Cuff: Influence of Arm Position].

Diffusion tensor imaging (DTI) of skeletal muscles has been reported as capable to characterize physiological properties, tissue microstructure and architectural organization. However, the DTI indices may vary with the contractile state of the muscles, and in the rotator cuff muscles, a change in forearm position can result in variation of the DTI indices. The purpose of this study was to examine the influence of forearm position on the major DTI indices of the rotator cuff muscles. The DTI of right rotator cuff was acquired under the neutral position and external and internal rotation of the forearm in nine healthy volunteers. Fractional anisotropy (FA) and mean diffusivity (MD) of each muscle were calculated and compared among the three forearm positions. FA and MD were significantly different between external and internal rotation in infraspinatus, teres minor and subscapularis (p<0.05). We considered that this difference was due to the change in cross-sectional area of muscle fibers based on their contractile state. That is, when the muscle is contracted, its cross-sectional area is increased and the muscle fiber density in the short axis direction becomes less. This causes a change in FA and MD due to increase in λ2 and λ3 through increased diffusion of intercellular water in the short axis direction. In conclusion, the DTI indices of the rotator cuff muscles are affected by the forearm position.