Shear wave elastography of the supraspinatus muscle and tendon: Repeatability and preliminary findings.

Shear wave elastography (SWE) is a promising tool for estimating musculoskeletal tissue properties, but few studies have rigorously assessed its repeatability and sources of error. The objectives of this study were to assess: (1) the extent to which probe positioning error and human user error influence measurement accuracy, (2) intra-user, inter-user, and day-to-day repeatability, and (3) the extent to which active and passive conditions affect shear wave speed (SWS) repeatability. Probe positioning and human usage errors were assessed by acquiring SWE images from custom ultrasound phantoms. Intra- and inter-user repeatability were assessed by two users acquiring five trials of supraspinatus muscle and tendon SWE images from ten human subjects. To assess day-to-day repeatability, five of the subjects were tested a second time, approximately 24h later. Imaging of the phantoms indicated high inter-user repeatability, with intraclass correlation coefficient (ICC) values of 0.68-0.85, and RMS errors of no more than 4.1%. SWE imaging of the supraspinatus muscle and tendon had high repeatability, with intra- and inter-user ICC values of greater than 0.87 and 0.73, respectively. Day-to-day repeatability demonstrated ICC values greater than 0.33 for passive muscle, 0.48 for passive tendon, 0.65 for active muscle, and 0.94 for active tendon. This study indicates the technique has good to very good intra- and inter-user repeatability, and day-to-day repeatability is appreciably higher when SWE images are acquired under a low level of muscle activation. The findings from this study establish the feasibility and repeatability of SWE for acquiring data longitudinally in human subjects.