In Vivo Measurement Method of the Speed of Sound in Cartilage Based on a Pseudo Point Scattered Wave Generation from Subchondral Bone Surface

Speed of sound (SoS) is expected to be non-invasively measured as an evaluation index for cartilage diseases such as knee osteoarthritis. In the conventional focusing method using a handheld probe, the SoS was determined based on the time delay correction of the scattered waves from a strong scattering point. However, since there is no strong scattering point in the cartilage, any improvements are necessary. In this study, we propose an improved focusing method, which performs full aperture focusing on transmission while varying the preset SoS, generates a pseudo point scattered wave from the subchondral bone surface, and then determines the SoS that maximizes the amplitude of the full aperture synthetic wave. The feasibility of the proposed method was verified by the experiments using cartilage phantoms and porcine chest cartilage.