ULTRASOUND STUDY OF BONE IN-VITRO

Ultrasound has been investigated as a tool for characterizing the biom echanical competence of bone. The rationale for using ultrasound rests on two points. First, its interaction with tissues can be used to mea sure their density, velocity, and structure, and thus to characterize the elasticity and to infer the strength of bone. Second, ultrasound m ay be used to characterize tissue properties over a wide range of spat ial dimensions and organizational levels, ranging from its constituent s (e.g., trabeculae for cancellous bone) to the entire organ' Differen t ultrasound techniques can be used to investigate diverse bone proper ties, but two techniques have emerged as having the potential for prov iding useful information on problems of current biomedical interest. T hese measure two parameters, density and velocity, which correlate wit h the elastic and ultimate properties of bone. In particular, the elas ticity E is formally related to the product of density and velocity sq uared, E = rhov2. Moreover, it has been shown by mechanical testing th at there is a single linear correlation between elasticity and strengt h at all orientations, both in cortical and in cancellous bone, materi als with a strong intrinsic anisotropy. At the tissue level, it may th erefore be expected that the ultrasound parameters will prove to be us eful predictors of bone strength and of its dependence on orientation. In vitro ultrasound studies have shown that these properties can be m easured specifically and quantitatively, and that they vary under diff erent physiological conditions.