Characterization of ultrasound attenuation and angular distribution from trabecular bone phantom material using refracto-vibrometry

Abstract

Ultrasound is being researched and used for diagnosing osteoporosis. Researchers use trabecular bone from humans as a test material, but such bone is bio-hazardous, not uniform, and of limited size. Recently it has been demonstrated that the open-cell polyurethane foam, known as “Sawbones” could be utilized as a substitute for trabecular bone in ultrasound studies. In the current study, rectangular slices of Sawbones trabecular bone phantom material were insonified with a 25 mm diameter 500 kHz ultrasound transducer oriented both normal to the surface and at an angle. Refracto-vibrometry (RV), an interferometric method for optically measuring ultrasound, was compared with conventional transducer measurements of ultrasound transmission through the bone phantom samples. The measurement beam from a Polytec PSV-400 scanning laser Doppler vibrometer was directed through a water tank towards a stationary retroreflective surface. Acoustic wave fronts (density variations) which pass through the ~50µm diameter measurement laser cause variations in the integrated optical path length. The measured signals were used to determine parameters such as normalized broadband ultrasonic attenuation (nBUA) at numerous scan points. This enabled measurements of the spatial and angular distribution of the transmitted ultrasonic field through the sample that are not possible using a conventional single-element ultrasonic transducer.