Investigation on anisotropy of elastic properties in tendon using shear wave elasticity imaging

Non-invasive evaluation of tendon structure and function is of great use clinically. We proposed that the shear wave elasticity imaging has a better potential in differentiating normal and destructed tendon tissue than high frequency sonography. Four in vitro porcine tendons were studied in this research. High frequency ultrasound could provide good spatial resolution to monitor the detail structure changes by collagenase alterations. By analyzing the speckle changes based on defining a signal to noise ratio (SNR), we could quantitatively estimate the structure differences. The SNR alteration in the region of interest (ROI) before and after collagenase injection is close to 4%. The changes induced by structure alterations are not obvious even through in high frequency ultrasound imaging. Further to analyze the changes of shear wave speed, the differences before and after collagenase injection in longitudinal and transverse section of tendon were 21.3% and 8.3%, respectively. From our results, we found the changes of shear wave speed were much more than speckle intensity alterations after collagenase injection. Moreover, the decrease ratio of shear wave speed in longitudinal section is much more than in transverse section. In other words, to diagnose the tendon disease could prior to investigate on the changes of mechanical property in longitudinal section of tendon. The changes of shear wave speed could provide a batter characteristic for differentiation of normal or diseased tissue.