Ultrasonic propagation in cancellous bone

The theoretical modelling of ultrasonic propagation in cancellous bone is pertinent to the improvement of ultrasonic techniques for diagnosing the bone disease osteoporosis. For such techniques to be confidently used in the clinical management of osteoporosis, fundamental research is required to establish an understanding of how ultrasonic waves travel in porous, or cancellous bone. This thesis concerns investigation into various theoretical models of propagation in porous media. These studies are supported by in vitro experiments on bovine cancellous bone around 1 MHz. Previous applications to bone of established theories, such as Biot's theory for fluid-saturated porous media, have enjoyed limited success. This thesis begins by considering Biot's theory in more detail than previously reported in the literature. Biot's theory predicts that two longitudinal waves travel in cancellous bone in response to insonation with a single wave. The existence of two waves, known as fast and slow waves, is confirmed, which had not been reported in the literature prior to the start of this work. The importance of the presence of marrow in the pores on these waves is investigated. The phase velocities of fast and slow waves are observed to be strongly dependent on direction, relative to the internal cancellous structure. However, the isotropic form of Biot is not appropriate for modelling this response. Therefore, a second approach is proposed, which uses Schoenberg's theory to model propagation in a parallel-plate model of cancellous bone. Direction dependent measured velocities are observed to give qualitative agreement with the predictions of the Schoenberg model. The two theoretical approaches are compared when anisotropic mechanical and fluid motion effects are introduced into Biot's theory.