The contribution of absorption to tissue attenuation

The relative contributions of ultrasonic scattering and absorption to the overall attenuation coefficient of tissues is an important issue in diagnostic and therapeutic ultrasound. This paper presents a range of experimental evidence and case studies which support the postulate that absorption dominates attenuation in soft tissues. Comparisons of tissue absorption coefficients (using thermal pulse decay) and attenuation coefficients (using radiation force insertion loss) are given, along with results of tissue homogenization experiments. Other evidence is gained from measurements of total scattered power, and clinical observations of backscatter and attenuation of focal lesions. Finally, comparisons are made of the attenuation of dilute protein solutions and whole liver specimens, in order to establish the role of multiple relaxation mechanisms at the macromolecular level in the overall attenuation coefficient of mammalian liver tissue.