Ultrasonic slow waves in air-saturated cancellous bone

This paper describes preliminary observations of ultrasonic wave propagatio n in air-saturated defatted cancellous bone from the human vertebra. Using a broadband pulse transmission system, attenuation and phase velocity were measured over a wide frequency range (100 kHz-1 MHz). The observed behaviou r was consistent with that expected for the decoupled slow wave predicted b y Blot's theory. Velocity was lower than that of free air, and there was ma rked frequency-dependent attenuation and velocity dispersion. The tortuosit y (alpha) of the trabecular microstructure was estimated from the high freq uency limit of the dispersion curve, with a mean value of alpha=1.040+/-0.0 04 obtained in five specimens. Ultrasonic measurements in air represent a v aluable new approach, capable of yielding parameters that directly characte rise bone structure. Furthermore, they may give useful insights into wave p ropagation in bone in vivo, where the trabecular framework is saturated wit h marrow fat rather than air. (C) 1999 Elsevier Science B.V. All rights res erved.