Evidence for mechanisms of ultrasonic attenuation in tissue derived from measurements on myocardium

Abstract

Although reports have suggested that protein content, especially collagen content, may be a significant determinant of the acoustic properties of soft tissue, the responsible mechanisms have not been established. Two classes of mechanisms have been considered: (1) structural, conformational, or chemical relaxations of the macromolecular constituents, and (2) processes arising from the inhomogeneous nature of tissue, such as viscous relative motion. As an approach toward identifying the mechanisms, the present investigations address quantitatively the relationship between the ultrasonic attenuation and certain physical properties of myocardial tissue. Myocardial infarction provides a method for investigating the relationship between collagen content and the ultrasonic attenuation, since increased concentration of collagen has been reported in areas of infarct. Collagen concentration was determined quantitatively using an assay for hydroxyproline. Measurements were conducted in vitro on approximately 900 sites from 60 dogs. The dependence of the ultrasonic attenuation on frequency and temperature, as well as on collagen concentration, was investigated to provide evidence of the mechanisms responsible for the attenuation.