Characterizing tendon microstructure using metrics associated with the angular dependence of ultrasound backscatter.

A high-frequency, quantitative ultrasound technique, based on the angular dependence of the ultrasound backscatter (AIB), was developed to characterize tendon microstructural alignment and detect alterations in alignment with diabetes and aging. Backscattered echoes (58-MHz, bandwidth 31-86 MHz) were obtained from murine tail tendon, skin, and liver at 31 insonation angles. AIB parametric images and the average AIB for a region-of-interest were computed at each angle. AIB measurements were angular-dependent in tendons having aligned collagen fibers and were angular-independent in skin and liver. Quantitative ultrasound metrics characterizing AIB as a function of insonation angle included (1) AIB¯N,max, the maximum AIB; (2) ΔAIB¯N, the change in AIB within ten degrees of its maximum; and (3) M, the linear rate of change of the derivative of the AIB as a function of insonation angle. All three metrics were significantly different in murine aged, wild-type tendons and young, diabetic tendons compared to young, wild-type tendons, indicating that scattering strength was reduced, and tendon disorganization was increased in aged, wild-type tendons and young, diabetic tendons compared to young, wild-type tendons. This work demonstrates the utility of an ultrasound technique employing metrics associated with the angular dependence of ultrasound backscatter to characterize tendon microstructure non-invasively.