Estimating the properties of bone phantom cylinders through the inversion of axially transmitted low-frequency...

Early detection of osteoporosis has increasingly focused on ultrasonic methods, particularly guided waves in axial transmission to assess cortical bone properties. This study demonstrates the potential of low-frequency measurements (<500 kHz) for accurately inferring cortical mechanical and geometrical properties. A custom ultrasonic transducer centered at 350 kHz was used to acquire data, processed via a 2D fast Fourier transform to obtain dispersion curves. These were compared with simulations generated using the semi-analytical iso-geometric analysis (SAIGA) method, modeling a quasi-cylindrical bone geometry in void or immersed in olive oil. By incorporating an excitability parameter into the inversion algorithm, the proposed method achieved a less than 5% discrepancy between bone phantom properties determined via SAIGA inversion and bulk wave pulse-echo measurements, demonstrating its accuracy and potential for in vivo applications. Results also showed that high-wavenumber modes predominantly reflect material properties, whereas low-wavenumber modes below 100 kHz are sensitive to the overall bone geometry, highlighting the importance of low frequencies for a global bone characterization.