Quantitative assessment of the rotator cuff using various advanced imaging techniques has recently gained interest, with the aim of identifying biomarkers to assist in surgical management following rotator cuff tears [1, 2]. It has been observed that the pennation angle (PA) is sensitive to early pathological muscle changes (i.e., fatty infiltration and musculotendinous retraction) following rotator cuff injury [3, 4] and may be useful to predict the outcome following surgical cuff repair.

Therefore, the objective of this study was to develop a low-complex two-dimensional method to measure PAs of the supraspinatus (SSP) muscle using DTI and to evaluate its test-retest reliability, inter-reader agreement, and intra-reader agreement.

Among the imaging techniques that are capable of visualizing muscular architecture, diffusion tensor imaging (DTI) has been successfully used to characterize the microstructure of healthy and pathological skeletal muscle [5]. Due to the structural anisotropy of muscle fibers, it is possible to compute a diffusion tensor that reveals the primary direction of diffusion (the first Eigenvector of the tensor), and to provide information about diffusion anisotropy and diffusion magnitude. These data then facilitate the estimation of architectural parameters such as the PA [6] or by integrating the information from adjacent voxels, the three-dimensional (3D) reconstruction of the fiber trajectory known as “tractography”.