The Mechanism of the Absorption of Ultrasound in Biological Materials

1) Absorption of sound in solutions of macromolecules has been found to be comparable in magnitude and similar in frequency dependence to that of tissues and blood. The absorption has been shown to arise through a relaxation process. Several experimental observations suggest that the relaxation may be related to the protein-water interactions. 2) The absorption of sound in normal blood, although predominately a molecular process, has in addition a component arising from the relative motion between the cells and the plasma. 3) In certain tissues, the experimental evidence points out again the importance of direct molecular absorption. This may be modified to some extent in inhomogeneous tissues where there is the possibility of selective absorption arising at macroscopic discontinuities.