Mechanism of absorption of ultrasound in liver tissue.

The dominant part of the acoustic absorption of liver tissue and its components results from macromolecular relaxation processes. The absorption has been investigated over the frequency range 1–10 MHz and the following results have been obtained: (1) About two‐thirds of the total absorption arises at the macromolecular level, with the remainder caused by macroscopic structure. (2) The specific absorption of tissue macromolecules, as expressed in absorption per weight percent, varies considerably from one biopolymer to another. (3) The absorption is related to the structure of the biological macromolecule or its hydration and changes with heat denaturation and pH. (4) A similar frequency dependence results for all materials investigated. This dependence is to be expected if one assumes that the molecular processes of absorption are characterized by a broad spectrum of relaxational time constants and activation energies extending over a range of at least 1:7.