Physical models of cortical bone conditions, fabricated by a 3D printer to test for sensitivity of axial transmission technique

Conditions of bone health such as variations of the thickness of cortical layer, intracortical porosity and low mineralization were simulated by a series of phantoms made of hard plastics using 3D printing. The phantoms presented edge-type strips mimicking cortical layer of long bones with a known gradient of the thickness by the length. Ultrasonic testing was performed as profiling by the phantoms' length in the axial transmission mode at frequencies 75 and 500 kHz through a covering soft layer and building time-distance plots of acquired signals. The results demonstrated ability of the axial transmission technique to discriminate between different simulated bone conditions in the presence of soft layers of varied thickness, as well as alternating the wave patterns by the soft layer with its specific features at low and high frequencies. The study indicates the need to incorporate the frequency-specific soft tissue factor in the comprehensive analysis of bone condition based on temporal and attenuation parameters of ultrasound propagation.