Influence of bone tissue density and elasticity on ultrasound propagation:An in vitro study

Ultrasound (US) waves are mechanical vibrations that are applied to a mater ial-bone tissue-in order to study its properties, that is, density, elastic ity, and structure. In this study we evaluated in which way density and ela sticity of the spongy bone influenced the transmission of 1.25 MHz US pulse s. Twelve cylindrical specimens (diameter, 8 mm; height, 5 mm) excised from phalanxes of pig were decalcified with 0.5 M EDTA for different times (0, 2, and 5 days). During these periods, the samples underwent the following i nvestigations: US transmission, density, and elasticity measurements. To as sess the homogeneity of decalcification, the cross-sections of some samples were microradiographed. A detailed analysis of the US signal received was performed using velocity, Fourier analysis, and some parameters typical of signal processing technique. A good correlation was found between US veloci ty and density (r(2) = 0.70); a lower correlation was found between velocit y and elasticity (r(2) = 0.59). If density and elasticity are considered si multaneously, the correlation with the US velocity improves significantly ( r(2) = 0.84). Fourier analysis enabled us to observe a shift of the main fr equency toward lower values as the decalcification process advanced. We als o observed that in the regressions weighted for density, US velocity correl ated poorly with elasticity (r(2) = 0.16), whereas signal processing parame ters maintain a good correlation with elasticity (ultrasound peak amplitude [UPA], r(2) = 0.48; slope, r(2) = 0.62). In this study, it has been observ ed that when using a signal processing technique to analyze US pulses, it i s possible to identify some parameters that are related in different ways t o density and to elastic properties of bone. Our results show the potential ity of US technique to separate information on bone density and elasticity that X-ray-based densitometric methods do not provide.