Dependence of the Ultrasonic Properties of Biological Tissue on Constituent Proteins

The study described herein was undertaken to determine the role of proteins, in general, and collagen, in particular, in the observed absorption and speed of ultrasound in biological tissues. It had earlier been observed that ultrasonic absorption in tissues occurs at the macromolecular level, •'z though an additional contribution to attenuation arises from tissue structural features. a Each of the molecular constituents of tissue, e.g., protein, lipid, water, etc., might then be expected to contribute to the absorption properties of an integrated tissue they comprise, and to do so in some proportion to their content. Thus, lipids would not be considered to contribute greatly to the ultrasonic absorption of most tissues, since they comprise only a small fraction of the wet weight? Though water comprises 70-80% of most biological tissues, 4 it exhibits a relatively small intrinsic absorption coefficient, being a few percent of the attenuation coefficient of parenchymal tissues in the low megahertz frequency region. s Proteins, however, in sufficient concentration in aqueous solution have been found to exhibit magnitudes of absorption coefficient in the same range as those of tissue attenuation. 6,7 Similar results have also been reported for ultrasonic velocity. a Furthermore, the absorption coefficient and velocity of high-frequency sound in blood and in protein solutions have been shown to be dependent on the protein concentration. '.s,7, a Additionally, some degree of correlation appears to exist between tissue constituent contents, when taken singly, and velocity and attenuation of ultrasoundfi -•l