Circumferential guided wave measurement in a cortical bone-mimicking cylindrical phantom

It is well accepted that direct quantitative ultrasound (QUS) measurements at the hip may improve osteoporotic fracture risk prediction. It has recently been reported that the cortical shell at the femoral neck behaves as a waveguide supporting the propagation of circumferential waves. In this study, the extension of the DORT method (Decomposition of the Time Reversal Operator) [C. Prada et al., J. Acoust. Soc. Am. 104, 801-807 (1998)] to the measurement of circumferential guided mode the phase velocities in a tube of bone mimicking phantom is proposed. The scattering response of the phantom was measured with a dedicated 128-element cylindrically focused array working in the frequency bandwidth 0.4-1.6 MHz. Several guided modes (A, A₁, S₁, S₂ and A₃) could be identified and their measured phase velocities were in good agreement with the fluid-loaded plate model and simulated experiments. These results suggest that the inverse problem can be solved with the aim of characterizing the thickness and elastic properties of the waveguide, which represent a significant step towards future bone applications.