Dispersion curve measurements of a fluid filled femoral neck mimicking phantom

Quantitative ultrasonic measurements at the hip are supposed to improve fracture risk prediction. The cortical shell of the femoral neck is now known to behave as a waveguide, supporting the propagation of circumferential waves. Measurement of circumferential waves dispersion curves using the DORT method (Decomposition of the time reversal operator [1]) on an empty tube of bone mimicking material was recently reported. In the present study, the method is adapted to the measurement of the dispersion curves of a tube of bone-mimicking material filled with a marrow-mimicking fluid. Difficulty compared with the empty tube arises from interferences of reflections on cavity walls with circumferential waves. Mixing of these two contributions makes the identification of guided waves focal spots in the backpropagation plane difficult. Based on comparison of results of two simulated experiments, involving separately the two contributions, a criterion of selection of relevant focal spots was proposed. Filtering of the backpropagation plane using this criterion was added to the DORT process and then applied to experimental and simulated signals. Several branches of dispersion curves were experimentally obtained.