Ultrasonic characteristics of in vitro human cancellous bone

Abstract

Cancellous bone is comprised of a connected network of trabeculae and is considered as an inhomogeneous and anisotropic acoustic medium. The fast and slow longitudinal waves are clearly observed when the ultrasonic wave propagates parallel to the direction of the trabeculae. The propagation speed of the fast wave increases with bone density and that of the slow wave is almost constant. The fast wave amplitude increases proportionally and the slow wave amplitude decreases inversely with bone density. Human in vitro femoral head was sectioned to 10-mm-thick slices perpendicularly to the femoral cervical axis. These cancellous bone samples were subjected to the ultrasonic measurement system LD-100 using a narrow focused beam. The propagation speed and the amplitude of the transmitted wave both for the fast and slow waves were measured at 1-mm intervals. The local bone density corresponding to the measured points was obtained using a microfocus x-ray CT system. Experimental results show that the propagation speeds and amplitudes for the fast and slow waves are characterized not only by the local bone density, but also by the local trabecular structure.